Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Akihide Fujisawa Last modified date:2020.06.22

Professor / Division of Nuclear Fusion Dynamics / Research Institute for Applied Mechanics


Papers
1. Fumiyoshi KIN, Kimitaka ITOH, Tim HAPPEL, Gregor BIRKENMEIER, Akihide FUJISAWA, Sigeru INAGAKI, Sanae-I. ITOH, Ulrich STROTH and ASDEX Upgrade Team, Comparison of Conditional Average Using Threshold and Template Methods for Quasi-Periodic Phenomena in Plasmas, Plasma and Fusion Research, Volume 14, 1402114, 2019.06.
2. H. Arakawa, Makoto Sasaki, Inagaki Shigeru, Yusuke Kosuga, T. Kobayashi, Naohiro Kasuya, Takuma Yamada, Yoshihiko Nagashima, F. Kin, akihide fujisawa, K. Itoh, S. I. Itoh, Roles of solitary eddy and splash in drift wave-zonal flow system in a linear magnetized plasma, Physics of Plasmas, 10.1063/1.5094577, 26, 5, 2019.05, We experimentally investigate the roles of drift wave type fluctuations interacting with zonal flow. The drift wave type fluctuations examined in this paper are characterized by nonlinear solitary wave, splash, and solitary eddy [Arakawa et al., Sci. Rep. 6, 33371 (2016)]. Compared to the nonlinear solitary wave, splash has a short lifetime, while solitary eddy has a long lifetime. Excitation/damping of the splash and the solitary eddy are synchronized with zonal perturbation. The roles of the splash and the solitary eddy in transport processes are also discussed. Solitary eddy contributes to momentum transport and accelerates zonal flow. The particle flux driven by the solitary eddy and the splash is in the inward and outward directions, respectively, with similar magnitudes..
3. F. Kin, akihide fujisawa, K. Itoh, Yusuke Kosuga, Makoto Sasaki, Inagaki Shigeru, Yoshihiko Nagashima, Takuma Yamada, Naohiro Kasuya, K. Yamasaki, K. Hasamada, B. Y. Zhang, Y. Kawachi, H. Arakawa, T. Kobayashi, S. I. Itoh, Observations of radially elongated particle flux induced by streamer in a linear magnetized plasma, Physics of Plasmas, 10.1063/1.5093218, 26, 4, 2019.04, The streamer-driven particle flux is evaluated experimentally in a linear cylindrical plasma. The streamers, a radially elongated and azimuthally localized structure created in turbulent plasma, really induce ballistic transport, and directly connect the plasma core to the edge within one order faster time scale than that of turbulence. The occurrence of large transport deviates from a Gaussian distribution and is likely to obey a power law. The fundamental plasma experiment clearly shows the significant and essential contributions of streamers to cross-field transport and structural formation of turbulent plasmas..
4. akihide fujisawa, Yoshihiko Nagashima, K. Yamasaki, Inagaki Shigeru, Takuma Yamada, Makoto Sasaki, Combined methods of moment vectors and Stokes parameters to analyze tomographic image of plasma turbulence, Physics of Plasmas, 10.1063/1.5048970, 26, 1, 2019.01, Plasma turbulence tomography is now working to show a two dimensional structure and dynamics of plasma turbulence in a cylindrical plasma device, PANTA. A new method, the Stokes parameter analysis on moment vectors, is being developed to treat the image of plasma turbulence and extract hidden characteristics of polarization or rotation of spatial patterns created in turbulent plasmas. The article presents the explanation of the method and the application results obtained from a PANTA plasma..
5. A. Shimizu, akihide fujisawa, S. Ohshima, H. Nakano, T. Minami, M. Isobe, S. Okamura, K. Matsuoka, Density profile measurement with a heavy ion beam probe in a toroidal plasma of the compact helical system, Review of Scientific Instruments, 10.1063/1.5039571, 89, 11, 2018.11, A possibility of electron density measurements with heavy ion beam probes (HIBPs) has been demonstrated, along with their capability to measure the potential and magnetic field. A method has been proposed to reconstruct the electron density profile [A. Fujisawa et al., Rev. Sci. Instrum. 74, 3335 (2003)]. In the method, the profile of secondary beam currents is converted into a local density profile by taking into account local brightness and so-called path integral effects which mean the effect of beam attenuation along the beam orbit. Here the article presents the HIBP measurement of the electron density profile after the proposed method was first applied on the real experimental data of compact helical system plasmas. In the real application, the hollow density and the peaked profiles are successfully obtained with sufficiently high temporal resolution (a few ms), in accordance with the electron density profile measured with Thomson scattering for electron cyclotron resonance heating and neutral beam injection plasmas..
6. Makoto Sasaki, K. Itoh, T. Kobayashi, Naohiro Kasuya, akihide fujisawa, Sanae Itoh, Propagation direction of geodesic acoustic modes driven by drift wave turbulence, Nuclear Fusion, 10.1088/1741-4326/aad251, 58, 11, 2018.10, Selection rule of the radial propagation direction of geodesic acoustic modes (GAMs) is investigated. Here, we study the influence of nonlinear coupling with drift wave turbulence on the propagation direction of GAMs. Based on wave-kinetic equation for the turbulence, the phase-space dynamics is numerically solved and the nonlinear saturated states are obtained, where the phase-space consists of the real space and the wavenumber space. A wave pattern of the GAM in a nonlinear saturated state varies to form a standing wave, outward and inward propagating waves, depending on the peak radial wavenumber of the turbulence. The impact of nonlinear coupling with turbulence is discussed by deriving the GAM dispersion relation that includes the effect of the turbulence..
7. Yoshihiko Nagashima, akihide fujisawa, Experimental research plan of nonlinearity of tokamak edge turbulence in plasma turbulence observatory, Front-runners� Symposium on Plasma Physics in Honor of Professors Kimitaka Itoh and Sanae-I. Itoh, 2018 Front-runners' Symposium on Plasma Physics in Honor of Professors Kimitaka Itoh and Sanae-I. Itoh, 10.1063/1.5048716, 2018.08, A set of experimental works based on nonlinear data analysis in the JFT-2M is planned in order to verify nonlinearity of edge turbulence in PLAsma Turbulence Observatory (PLATO) tokamak. In this paper, we introduce the preceding experimental works of the JFT-2M tokamak, and show how the revisited works are applied to progress of turbulence research in the new tokamak..
8. akihide fujisawa, Past and present experiments toward PLATO project, Front-runners� Symposium on Plasma Physics in Honor of Professors Kimitaka Itoh and Sanae-I. Itoh, 2018 Front-runners' Symposium on Plasma Physics in Honor of Professors Kimitaka Itoh and Sanae-I. Itoh, 10.1063/1.5048721, 2018.08, Plasma turbulence has been intensively studied in the research of magnetic confinement for realizing a nuclear fusion reactor, and the international research has provided various discoveries of and physics insights into turbulent plasmas, such as turbulence-driven transport, effects of electric field on confinement, generation of flows and fields, and so on, although the research has been performed with a strong weight on achieving fusion-relevant performance plasma. However, at present a project to construct a physics-oriented device, named PLAsma Turbulence Observatory (PLATO), in Kyushu University, aiming at essential physics understanding of turbulent plasmas. The article reviews the major physics achievements up to data, and the steps to reach the concept of a new toroidal device with the major purpose for physics understanding of plasma turbulence..
9. Yuichi KAWACHI, Sigeru INAGAKI, Kentaro TOMITA, Kotaro YAMASAKI, Fumiyoshi KIN, Yusuke KOSUGA, Makoto SASAKI, Yoshihiko NAGASHIMA, Naohiro KASUYA, Kazunobu HASAMADA, Boyu ZHANG, Akihide FUJISAWA, Determination of Spatiotemporal Structure of Fluctuations by Statistical Averaging Method, Plasma and Fusion Research, 13, 3401105, 2018.08.
10. Santanu Banerjee, H. Zushi, N. Nishino, Kazuaki Hanada, Hiroshi Idei, K. Nakamura, Makoto Hasegawa, akihide fujisawa, Yoshihiko Nagashima, K. Mishra, S. Tashima, Takumi Onchi, A. Kuzmin, K. Matsuoka, Effect of magnetic shear on edge turbulence in SOL-like open field line configuration in QUEST, Plasma Physics and Controlled Fusion, 10.1088/1361-6587/aacb69, 60, 8, 2018.06, Intensity fluctuations are investigated using the fast camera imaging technique in the slab annular plasma as a function of magnetic shear and connection length in the spherical tokamak QUEST. Note that here QUEST is operated as a simple magnetized torus with a tight aspect ratio. Slab annular plasmas feature open magnetic field lines and can mimic the tokamak edge-scrape off layer (SOL)-like plasma attributes reasonably well. Three magnetic shear regimes are realized using three poloidal magnetic field (PF) coil pairs. A whole range of connection lengths (∼∞ ≥ L c ≥ 5.5 m) is scanned by varying the PF strength for a given toroidal field for each magnetic shear regime. For the first time a systematic study of the effect of magnetic shear and field line pitch together on edge-SOL-like plasma fluctuations is being reported. Slab plasmas with intermediate magnetic shear are observed to be more susceptible to generate distinct blobs when L c is reduced by increasing the PF strength. A distinct coherent mode appears only at the lowest magnetic shear slab featuring a deep potential well. Such mode is not apparent at other magnetic shear cases even at the same L c. Finally, with a combination of PF coil pairs, both the features of intermediate and low magnetic shear slabs are shown to be realizable simultaneously. Significantly stronger blobs are observed with such combination of PF mirror ratios in the presence of a coherent mode. This study may provide better insight into the effect of magnetic configuration in the tokamak edge and SOL turbulence and can help in searching for better tools to control cross-field convective intermittent transport in tokamaks..
11. F. Kin, K. Itoh, akihide fujisawa, Yusuke Kosuga, Makoto Sasaki, Takuma Yamada, Inagaki Shigeru, Sanae Itoh, T. Kobayashi, Yoshihiko Nagashima, Naohiro Kasuya, H. Arakawa, K. Yamasaki, K. Hasamada, Extraction of nonlinear waveform in turbulent plasma, Physics of Plasmas, 10.1063/1.5027124, 25, 6, 2018.06, Streamers and their mediator have been known to exist in linear cylindrical plasmas [Yamada et al., Nat. Phys. 4, 721 (2008)]. Conditional averaging is applied to extract the nonlinear characteristics of a mediator, which has been simply treated as a linear wave. This paper reports that a mediator should have higher harmonic components generated by self-couplings, and the envelope of a streamer should be generated with not only fundamental but also higher harmonic components of the mediator. Moreover, both the mediator and the envelope of the streamer have common features with solitary waves, i.e., the height should increase inversely as the square of their localization width..
12. Yamada, T., Inagaki, S., Sasaki, M., Nagashima, Y., Kin, F., Arakawa, H., Kobayashi, T., Yamasaki, K., Kasuya, N., Kosuga, Y., Fujisawa, A., Itoh, K., Itoh, S.-I., Three-dimensional structure of the streamer in linear plasmas, Journal of the Physical Society of Japan, DOI: 10.7566/JPSJ.87.034501, 87, 3, 034501, 2018.05.
13. Sasaki, M., Kobayashi, T., Itoh, K., Kasuya, N., Kosuga, Y., Fujisawa, A., Itoh, S.-I., Spatio-temporal dynamics of turbulence trapped in geodesic acoustic modes, Physics of Plasmas, DOI: 10.1063/1.5008541, 25, 1, 012316, 2018.05.
14. Kimitaka ITOH, Sanae-I. ITOH, Yoshihiko NAGASHIMA, Takuma YAMADA, Yusuke KOSUGA, Akihide FUJISAWA, Symmetry-Breaking of Turbulence Structure and Position Identification in Toroidal Plasmas, Plasma and Fusion Research, Volume 13 Pages 1102113, 2018.05.
15. Makoto SASAKI, Kimitaka ITOH, Takeshi IDO, Akihiro SHIMIZU, Tatsuya KOBAYASHI, Hiroyuki ARAKAWA, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I. ITOH, Evaluation of Measurement Signal of Heavy Ion Beam Probe of Energetic-Particle Driven Geodesic Acoustic Modes, Plasma and Fusion Research, 13, 3403040, 2018.05.
16. Kobayashi, T., Sasaki, M., Ido, T., Kamiya, K., Miura, Y., Nagashima, Y., Ida, K., Inagaki, S., Fujisawa, A., Itoh, S.-I., Itoh, K., Quantification of Turbulent Driving Forces for the Geodesic Acoustic Mode in the JFT-2M Tokamak, Physical Review Letters, DOI: 10.1103, 120, 045002, 2018.03.
17. Itoh, K., Itoh, S.I., Nagashima, Y., Yamada, T., Fujisawa, A., Position identification of measurement for the study of symmetry-breaking of turbulence structure in toroidal plasmas, Journal of the Physical Society of Japan, DOI: 10.7566, 87 , 2, 025002, 2018.01.
18. F. Kin, akihide fujisawa, K. Itoh, Yusuke Kosuga, Makoto Sasaki, Takuma Yamada, Inagaki Shigeru, S. I. Itoh, T. Kobayashi, Yoshihiko Nagashima, Naohiro Kasuya, H. Arakawa, K. Yamasaki, K. Hasamada, Nonlinear characteristics of mediator and streamer in linear magnetized plasmas, 45th EPS Conference on Plasma Physics, EPS 2018 45th EPS Conference on Plasma Physics, EPS 2018, 565-568, 2018.01.
19. Kobayashi, T., Itoh, K., Ido, T., Kamiya, K., Itoh, S.-I., Miura, Y., Nagashima, Y., Fujisawa, A., Inagaki, S., Ida, K., Hoshino, K., Model validation for radial electric field excitation during L-H transition in JFT-2M tokamak, Nuclear Fusion, 10.1088/1741-4326/aa5d03, 57, 7, 72005, 2017.05.
20. Onchi, T., Fujisawa, A., Sanpei, A., Himura, H., Masamune, S., Permutation entropy and statistical complexity in characterising low-aspect-ratio reversed-field pinch plasma, Physica Scripta, 10.1088/1402-4896/aa6689, 92, 5, 55601, 2017.05.
21. Zhao, K.J., Nagashima, Y., Diamond, P.H., Dong, J.Q., Itoh, K., Itoh, S.-I., Yan, L.W., Cheng, J., Fujisawa, A., Inagaki, S., Kosuga, Y., Sasaki, M., Huang, Z.H., Yu, D.L., Li, Q., Ji, X.Q., Song, X.M., Huang, Y., Liu, Y., Yang, Q.W., Ding, X.T., Duan, X.R., Mesoscale electric fluctuations interacting with zonal flows, magnetic fluctuations and turbulence, Nuclear Fusion, 57 , 7, 076036, 2017.05.
22. Kuzmin, A., Zushi, H., Takagi, I., Sharma, S.K., Kobayashi, M., Hirooka, Y., Onchi, T., Hanada, K., Yoshida, N., Nakamura, K., Fujisawa, A., Idei, H., Nagashima, Y., Hasegawa, M., Mutoh, T., Mishra, K., Ohwada, H., Spatial distribution of atomic and ion hydrogen flux and its effect on hydrogen recycling in long duration confined and non-confined plasmas, Nuclear Materials and Energy, DOI: 10.1016/j.nme.2017.03.027, 12, 627-632, 2017.05.
23. Wang, Z., Hanada, K., Yoshida, N., Shimoji, T., Miyamoto, M., Oya, Y., Zushi, H., Idei, H., Nakamura, K., Fujisawa, A., Nagashima, Y., Hasegawa, M., Kawasaki, S., Higashijima, A., Nakashima, H., Nagata, T., Kawaguchi, A., Fujiwara, T., Araki, K., Mitarai, O., Fukuyama, A., Takase, Y., Matsumoto, K., Measurement of thickness of film deposited on the plasma-facing wall in the QUEST tokamak by colorimetry, Review of Scientific Instruments, DOI: 10.1063/1.5000739, 88, 9, 093502, 2017.05.
24. Yamasaki, K., Fujisawa, A., Nagashima, Y., A proposal of Fourier-Bessel expansion with optimized ensembles of bases to analyse two dimensional image, Review of Scientific Instruments, DOI: 10.1063/1.5000744, 88, 9, 093507, 2017.05.
25. Zhao, K.J., Nagashima, Y., Li, F.M., Shi, Y., Diamond, P.H., Dong, J.Q., Itoh, K., Itoh, S.-I., Zhuang, G., Liu, H., Chen, Z.P., Cheng, J., Nie, L., Ding, Y.H., Hu, Q.M., Chen, Z.Y., Rao, B., Cheng, Z.F., Gao, L., Zhang, X.Q., Yang, Z.J., Wang, N.C., Wang, L., Jin, W., Yan, W., Xu, J.Q., Wu, Y.F., Yan, L.W., Fujisawa, A., Inagaki, S., Kosuga, Y., Sasaki, M., Temporal-spatial structures of plasmas flows and turbulence around tearing mode islands in the edge tokamak plasmas, Nuclear Fusion, 5, 12, 126006, 2017.05.
26. Idei, H., Kariya, T., Imai, T., Mishra, K., Onchi, T., Watanabe, O., Zushi, H., Hanada, K., Qian, J., Ejiri, A., Alam, M.M., Nakamura, K., Fujisawa, A., Nagashima, Y., Hasegawa, M., Matsuoka, K., Fukuyama, A., Kubo, S., Shimozuma, T., Yoshikawa, M., Sakamoto, M., Kawasaki, S., Nakashima, H., Higashijima, A., Ide, S., Maekawa, T., Takase, Y., Toi, K., Fully non-inductive second harmonic electron cyclotron plasma ramp-up in the QUEST spherical tokamak, Nuclear Fusion, DOI: 10.1088/1741-4326/aa7c20, 57, 12, 126045, 2017.05.
27. Hanada, K., Yoshida, N., Honda, T., Wang, Z., Kuzmin, A., Takagi, I., Hirata, T., Oya, Y., Miyamoto, M., Zushi, H., Hasegawa, M., Nakamura, K., Fujisawa, A., Idei, H., Nagashima, Y., Watanabe, O., Onchi, T., Kuroda, K., Long, H., Watanabe, H., Tokunaga, K., Higashijima, A., Kawasaki, S., Nagata, T., Takase, Y., Fukuyama, A., Mitarai, O., Investigation of hydrogen recycling in long-duration discharges and its modification with a hot wall in the spherical tokamak QUEST, Nuclear Fusion, 57, 12, 126061, 2017.05.
28. Nakamura, K., Alam, M.M., Jiang, Y.Z., Mitarai, O., Kurihara, K., Kawamata, Y., Sueoka, M., Takechi, M., Hasegawa, M., Tokunaga, K., Araki, K., Zushi, H., Hanada, K., Fujisawa, A., Idei, H., Nagashima, Y., Kawasaki, S., Nakashima, H., Higashijima, A., Nagata, T., Fukuyama, A., Plasma equilibrium based on RF-driven current profile without assuming nested magnetic surfaces on QUEST, Fusion Engineering and Design, 123, 532-534, 2017.05.
29. Sasaki, M., Kasuya, N., Itoh, K., Toda, S., Yamada, T., Kosuga, Y., Nagashima, Y., Kobayashi, T., Arakawa, H., Yamasaki, K., Fujisawa, A., Inagaki, S., Itoh, S.-I. , Topological bifurcation of helical flows in magnetized plasmas with density gradient and parallel flow shear, Physics of Plasmas, DOI: 10.1063/1.5000343, 24, 11, 112103, 2017.05.
30. Kobayashi, T., Itoh, K., Ido, T., Kamiya, K., Itoh, S.-I., Miura, Y., Nagashima, Y., Fujisawa, A., Inagaki, S., Ida, K. , Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma, Scientific Reports , DOI: 10.1038/s41598-017-14821-y, 7, 1, 14971, 2017.05.
31. Nakamura, K., Alam, M.M., Jiang, Y.Z., Mitarai, O., Kurihara, K., Kawamata, Y., Sueoka, M., Takechi, M., Hasegawa, M., Tokunaga, K., Araki, K., Zushi, H., Hanada, K., Fujisawa, A., Idei, H., Nagashima, Y., Kawasaki, S., Nakashima, H., Higashijima, A., Nagata, T., Fukuyama, A., Analysis of plasma equilibrium based on orbit-driven current density profile in steady-state plasma on QUEST, Fusion Engineering and Design, 109-111, 1528-1533, 2016.05.
32. Itoh, K., Zhao, K., Dong, J., Itoh, S.-I., Fujisawa, A., Inagaki, S., Sasaki, M., Nagashima, Y., Kosuga, Y., Cheng, J., Kobayashi, T., A calibration of setting of mach probes by observing GAM oscillations, Plasma and Fusion Research, DOI: 10.1585/pfr.11.1402002, 11, 1402002, 2016.05.
33. Mitarai, O., Nakamura, K., Hasegawa, M., Onchi, T., Idei, H., Fujisawa, A., Hanada, K., Zushi, H., Higashijima, A., Nakashima, H., Kawasaki, S., Matsuoka, K., Koike, S., Takahashi, T., Tsutsui, H., Comparative studies of inner and outer divertor discharges and a fueling study in QUEST, Fusion Engineering and Design, DOI: 10.1016/j.fusengdes.2015.12.022, 109-111, 1365-1370, 2016.05.
34. Alam, M.M., Nakamura, K., Xia, F., Mitarai, O., Hasegawa, M., Tokunaga, K., Araki, K., Zushi, H., Hanada, K., Fujisawa, A., Idei, H., Nagashima, Y., Kawasaki, S., Nakashima, H., Higashijima, A., Nagata, T., Comparison of current density profiles based on particle orbit-driven current in steady-state plasma on QUEST, Fusion Engineering and Design, DOI: 10.1016/j.fusengdes.2015.11.007, 109-111, 1624-1630, 2016.05.
35. Kanzaki, T., Nagashima, Y., Inagaki, S., Kin, F., Miwa, Y., Sasaki, M., Yamada, T., Fujisawa, A., Kobayashi, T., Kasuya, N., Kosuga, Y., Itoh, S.-I., Itoh, K., Improvement of the reynolds stress probe for end-plate biasing experiments in a cylindrical laboratory plasma, Plasma and Fusion Research, DOI: 10.1585/pfr.11.1201091, 11, 1201091, 2016.05.
36. Inagaki, S., Kobayashi, T., Kosuga, Y., Itoh, S.-I., Mitsuzono, T., Nagashima, Y., Arakawa, H., Yamada, T., Miwa, Y., Kasuya, N., Sasaki, M., Lesur, M., Fujisawa, A., Itoh, K., A Concept of Cross-Ferroic Plasma Turbulence, Scientific Reports, DOI: 10.1038/srep22189, 6, 22189, 2016.05.
37. Idei, H., Mishra, K., Yamamoto, M.K., Hamasaki, M., Fujisawa, A., Nagashima, Y., Hayashi, Y., Onchi, T., Hanada, K., Zushi, H., Adaptive-Array electron cyclotron emission diagnostics using data streaming in a software defined radio system, Journal of Instrumentation, DOI: 10.1088/1748-0221/11/04/C04010, 11, 4, C04010, 2016.05.
38. Alam, M.M., Nakamura, K., Hasegawa, M., Tokunaga, K., Araki, K., Zushi, H., Hanada, K., Fujisawa, A., Idei, H., Nagashima, Y., Kawasaki, S., Nakashima, H., Higashijima, A., Xia, F., Mitarai, O., Current density calculation from particle orbit in RF-driven divertor plasma on QUEST, Proceedings - Symposium on Fusion Engineering, DOI: 10.1109/SOFE.2015.7482308, 7482308, 2016.05.
39. Kuzmin, A., Zushi, H., Takagi, I., Sharma, S.K., Hirooka, Y., Kobayashi, M., Sakamoto, M., Hanada, K., Onchi, T., Oyama, Y., Youshida, N., Nakamura, K., Fujisawa, A., Idei, H., Nagashima, Y., Hasegawa, M., Mishra, K., Hydrogen flux measurements with permeation probes in spherical tokamak QUEST, Vacuum, DOI: 10.1016/j.vacuum.2016.04.025, 129, 178-182, 2016.05.
40. Banerjee, S., Zushi, H., Nishino, N., Mishra, K., Mahira, Y., Tashima, S., Ejiri, A., Yamaguchi, T., Onchi, T., Nagashima, Y., Hanada, K., Nakamura, K., Idei, H., Hasegawa, M., Fujisawa, A., Kuzmin, A., Matsuoka, K., Observation of an edge coherent mode and poloidal flow in the electron cyclotron wave induced high βpplasma in QUEST, DOI: 10.1063/1.4960117, 23, 082507, 2016.05.
41. Kobayashi, T., Itoh, K., Ido, T., Kamiya, K., Itoh, S.-I., Miura, Y., Nagashima, Y., Fujisawa, A., Inagaki, S., Ida, K., Hoshino, K., Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas, Scientific Reports, DOI: 10.1038/srep30720, 30720, 2016.05.
42. Alam, Md.M., Nakamura, K., Idei, H., Hasegawa, M., Tokunaga, K., Araki, K., Hanada, K., Fujisawa, A., Nagashima, Y., Kawasaki, S., Nakashima, H., Higashijima, A., Xia, F., Mitarai, O., Guiding Center Orbit Calculation for Evaluating the Current Density Distributions of the Electrons in Electron Cyclotron Heating on QUEST, IEEE Transactions on Plasma Science, DOI: 10.1109/TPS.2016.2570815, 44, 7482769, 2016.05.
43. Kin, F., Yamada, T., Inagaki, S., Nagashima, Y., Arakawa, H., Kobayashi, T., Miwa, Y., Kasuya, N., Sasaki, M., Kosuga, Y., Fujisawa, A., Itoh, K., Itoh, S.-I., Changes of particle flux during end-plate biasing experiment in PANTA, Journal of the Physical Society of Japan, DOI: 10.7566/JPSJ.85.093501, 85, 093501, 2016.05.
44. Onchi, T., Zushi, H., Mishra, K., Oyama, Y., Nagashima, Y., Hanada, K., Idei, H., Hasegawa, M., Kuzmin, A., Miura, H., Nakamura, K., Fujisawa, A., Nagaoka, K., Response of the far scrape-off layer plasma to strong gas puffing in the high poloidal beta configuration of the QUEST spherical tokamak, Plasma Physics and Controlled Fusion, DOI: 10.1088/0741-3335/58/11/115004, 58, 115004, 2016.05.
45. Arakawa, H., Inagaki, S., Sasaki, M., Kosuga, Y., Kobayashi, T., Kasuya, N., Nagashima, Y., Yamada, T., Lesur, M., Fujisawa, A., Itoh, K., Itoh, S.-I., Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma, Scientific Reports, DOI: 10.1038/srep33371, 6, 33371, 2016.05.
46. Zhao, K.J., Nagashima, Y., Diamond, P.H., Dong, J.Q., Itoh, K., Itoh, S.-I., Yan, L.W., Cheng, J., Fujisawa, A., Inagaki, S., Kosuga, Y., Sasaki, M., Wang, Z.X., Wei, L., Huang, Z.H., Yu, D.L., Hong, W.Y., Li, Q., Ji, X.Q., Song, X.M., Huang, Y., Liu, Y., Yang, Q.W., Ding, X.T., Duan, X.R., Synchronization of Geodesic Acoustic Modes and Magnetic Fluctuations in Toroidal Plasmas, Physical Review Letters, 117, 145002, 2016.05.
47. Kobayashi, T., Inagaki, S., Kosuga, Y., Sasaki, M., Nagashima, Y., Yamada, T., Arakawa, H., Kasuya, N., Fujisawa, A., Itoh, S.-I., Itoh, K., Structure formation in parallel ion flow and density profiles by cross-ferroic turbulent transport in linear magnetized plasma, Physics of Plasmas, DOI: 10.1063/1.4965915, 23, 102311, 2016.05.
48. Hasegawa, M., Nakamura, K., Zushi, H., Hanada, K., Fujisawa, A., Tokunaga, K., Idei, H., Nagashima, Y., Kawasaki, S., Nakashima, H., Higashijima, A., Current status and prospect of plasma control system for steady-state operation on QUEST, Fusion Engineering and Design, DOI: 10.1016/j.fusengdes.2016.04.016, 112, 699-702, 2016.05.
49. Hanada, K., Zushi, H., Idei, H., Nakamura, K., Ishiguro, M., Tashima, S., Kalinnikova, E.I., Nagashima, Y., Hasegawa, M., Fujisawa, A., Higashijima, A., Kawasaki, S., Nakashima, H., Mitarai, O., Fukuyama, A., Takase, Y., Gao, X., Liu, H., Qian, J., Ono, M., Raman, R., Power Balance Estimation in Long Duration Discharges on QUEST, Plasma Science and Technology, DOI: 10.1088/1009-0630/18/11/03, 18 , 11, 1069-1075, 2016.05.
50. Nagashima Yoshihiko, K. Itoh, Sanae-I. Itoh, Fujisawa Akihide, K. Hoshino, Change in Edge Fluctuations Synchronized with Heat Pulse in the JFT-2M Tokamak, Journal of Physical Society of Japan, Japanese Physics Society, 10.7566/JPSJ.85.063501, 85, 063501-1-063501-4, 2016.04.
51. Akihide Fujisawa, 永島 芳彦, 稲垣 滋, 恩地 拓己, 大島伸介, 清水昭博, Tomography as a promising diagnostic tool for plasma turbulence, Institute of Physics, 10.1088/0741-3335/58/2/025005, 58, 025005-1-025005-10, 2016.01, A system for plasma turbulence tomography has been developed in a linear cylindrical plasma
as a prototype with aiming at future application on toroidal plasma of higher temperature. This paper describes the diagnostic system in both aspects of the soft- and hardware, and reports the first results of tomographic reconstruction that can successfully produce local emission and its fluctuations. In the reconstruction process, two dimensional view of plasma is obtained for approximately 0.6 ms in every sampling time of 1 μs using parallel processing of 120 cores with 10 personal computers. The results include the steady state analysis of local fluctuation power spectra using fast Fourier transform, analysis of temporal behavior of fluctuation power spectra with wavelet transform, and analyses of the structural deformation or pattern of local plasma emission, demonstrating that the success of tomography as a promising diagnostic tool for plasma turbulence..
52. H.Idei, MISHRA KISHORE KANTI, Yamamoto, M., Fujisawa Akihide, Nagashima Yoshihiko, Hamasaki, M., Hayashi, Y., Takumi Onchi, K.Hanada, zushi hideki, Multiple wall-reflection effect in adaptive-array differential-phase reflectometry on QUEST, JOURNAL OF INSTRUMENTATION, 10.1088/1748-0221/11/01/C01014, 11, 2016.01.
53. K. Itoh, Sanae-I. Itoh, S. Inagaki, Naohiro Kasuya, Fujisawa Akihide, On the Study of Higher Harmonics of Heat Pulse Propagation in the Modulated-Heating Experiments, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 10.7566/JPSJ.85.014501, 85, 1, 2016.01.
54. Kazuo Nakamura, M M Alam, YZ Jiang, O Mitarai, K Kurihara, Y Kawamata, M Sueoka, M Takech, Makoto Hasegawa, K. Tokunaga, K Araki, zushi hideki, K.Hanada, Fujisawa Akihide, H.Idei, Nagashima Yoshihiko, S Kawasaki, H Nakashima, A Higashijima, Analysis of plasma equilibrium based on orbit-driven current density profile in steady-state plasma on QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2015.11.035, 1-6, 2015.12.
55. O.Mitarai, Kazuo Nakamura, Makoto Hasegawa, Takumi Onchi, H.Idei, Fujisawa Akihide, K.Hanada, zushi hideki, A.Higashijima, H.Nakashima, S.Kawasaki, K.Matsuoka, S.Koike, T.Takahashi, H.Tsutsui, Comparative studies of inner and outer divertor discharges and a fueling study in QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2015.12.022, 2015.12.
56. Kobayashi, T., S. Inagaki, M. Sasaki, Kosuga, Y., Arakawa, H., Yamada, T., Nagashima Yoshihiko, Miwa, Y., Naohiro Kasuya, Fujisawa Akihide, Sanae-I. Itoh, Itoh, K., Azimuthal inhomogeneity of turbulence structure and its impact on intermittent particle transport in linear magnetized plasmas, PHYSICS OF PLASMAS, 10.1063/1.4934537, 22, 11, 112301-1-112301-8, 2015.11.
57. Md Mahbub Alam, Kazuo Nakamura, Fan Xia, Osamu Mitarai, Makoto Hasegawa, K. Tokunaga, Kuniaki Araki, zushi hideki, Fujisawa Akihide, H.Idei, Nagashima Yoshihiko, Shoji Kawasaki, Hisatoshi Nakashima, ki Higashijima, Takahiro Nagata, Comparison of current density profiles based on particle orbit-driven current in steady-state plasma on QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2015.11.007, 1-7, 2015.11.
58. Makoto Hasegawa, Kazuo Nakamura, zushi hideki, K.Hanada, Fujisawa Akihide, Mitarai, Osamu, K. Tokunaga, H.Idei, Nagashima Yoshihiko, Kawasaki, Shoji, Nakashima, Hisatoshi, Higashijima, Aki, Development of a high-performance control system by decentralization with reflective memory on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2015.06.054, 96-97, 629-632, 2015.10.
59. Aleksandrovich Arseniy Kuzmin, zushi hideki, Takagi, I., Sharma, S. K, RUSINOV ALEKSANDR, Inoue, Y., Y.; Hirooka, Zhou, H, Kobayashi, M., Mizuki Sakamoto, K.Hanada, Naoaki Yoshida, Kazuo Nakamura, Fujisawa Akihide, Matsuoka, K., H.Idei, Nagashima Yoshihiko, Makoto Hasegawa, Takumi Onchi, Global gas balance and influence of atomic hydrogen irradiation on the wall inventory in steady-state operation of QUEST tokamak, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2014.12.092, 463, 1087-1090, 2015.08.
60. Takumi Onchi, Mahira, Y., Nagaoka, K., Tashima, S., BANERJEE SANTANU, MISHRA KISHORE KANTI, H.Idei, K.Hanada, Kazuo Nakamura, Fujisawa Akihide, Nagashima Yoshihiko, Makoto Hasegawa, Matsuoka, K., Aleksandrovich Arseniy Kuzmin, Osamu Watanabe, Kawasaki, S., Nakashima, H., Higashijima, A., Observation of heat flux and plasma flow in scrape off layer in QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2014.11.136, 463, 428-431, 2015.08.
61. K.Hanada, zushi hideki, Naoaki Yoshida, Yugami, N., Honda, T., Makoto Hasegawa, MISHRA KISHORE KANTI, Aleksandrovich Arseniy Kuzmin, Kazuo Nakamura, Fujisawa Akihide, H.Idei, Nagashima Yoshihiko, Osamu Watanabe, Takumi Onchi, H. Watanabe, K. Tokunaga, Higashijima, A., Kawasaki, S., Nakashima, H., Particle balance in long duration RF driven plasmas on QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2015.01.013, 463, 1084-1086, 2015.08.
62. Kishore Mishra, zushi hideki, Fujisawa Akihide, H.Idei, Makoto Hasegawa, Takumi Onchi, Nagashima Yoshihiko, Saya Taslima, S Banerjee, K.Hanada, Self organization of high beta_p plasma equilibrium with an inboard poloidal magnetic field null in QUEST, IAEA Nuclear Fusion, 10.1088/0029-5515/55/8/083009, 55, 2015.07, Successful production of high βp plasmas (εβp ≥ 1) fully non-inductively (NI) and their long pulse sustainment with the help of modest power (<100 kW) of electron cyclotron waves is demonstrated. High βp plasmas are found for the first time to be naturall.
63. Hiroki Miura, K.Hanada, zushi hideki, Kazuo Nakamura, Fujisawa Akihide, H.Idei, Nagashima Yoshihiko, Makoto Hasegawa, Hisatoshi Nakashima, Shoji Kawasaki, Aki Higashijima, Osamu Mitarai, Atsushi Fukuyama, Yuichi Takase, Comparison between Non-Inductive Plasma Current Start-Up Using ECRH with and without Fundamental Resonance on QUEST, Plasma and Fusion Research, 10.1585, 10, 3402066-1-3402066-4, 10, 3402066, 2015.07.
64. Takumi Onchi, Kishore Mishra, Fujisawa Akihide, zushi hideki, H.Idei, K.Hanada, Makoto Hasegawa, Nagashima Yoshihiko, Heat flux and plasma flow in the far scrape-off layer of the inboard poloidal field null configuration in QUEST, Phys. Plasmas, http://dx.doi.org/10.1063/1.4928878, 55, 22, 082513-082513, 2015.05, Heat flux and plasma flow in the scrape-off layer (SOL) are examined for the inboard poloidal field null (IPN) configuration of the spherical tokamak QUEST. In the plasma current (I p) ramp-up phase, high heat flux (>1 MW/m2) and supersonic flow (Mach num.
65. T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, 伊藤 早苗, Y. Miura, 永島 芳彦, Akihide Fujisawa, 稲垣 滋, K. Ida, K. Hoshino, Edge plasma dynamics during L-H transition in the JFT-2M tokamak, Nucl. Fusion, 10.1088/0029-5515/55/6/063009, 55, 2015.05.
66. Nagashima Yoshihiko, S. Inagaki, Fujisawa Akihide, Hiroyuki Arakawa, Takuma Yamada, Yudai Miwa, Tatsuya Kobayashi,, Sanae-I. Itoh, Kimitaka Itoh, Observation of Parallel Force Balance for Drift Wave Fluctuation by a Fast Voltage Sweeping Method in a Linear Plasma, Journal of the Physical Society of Japan, 84, 6, 063501-1-063501-3, Volume 84, Number 6, 063501 (2015), 2015.05.
67. Takumi Onchi, Kishore Mishra, Fujisawa Akihide, zushi hideki, H.Idei, K.Hanada, Makoto Hasegawa, Nagashima Yoshihiko, Dynamical programming based turbulence velocimetry for fast visible imaging of tokamak plasma, Rev. Sci. Instrum, 10.1063/1.4914838, 86, 033505-1-033505-8, 2015.03, An orthogonal dynamic programming (ODP) based particle image velocimetry (PIV) technique is developed to measure the time resolved flow field of the fluctuating structures at the plasma edge and scrape
off layer (SOL) of tokamaks..
68. T. Yamada, S. Inagaki, T. Kobayashi, Y. Nagashima, T. Mitsuzono, Y. Miwa, K. Nakanishi, H. Fujino, M. Sasaki, N. Kasuya, M. Lesur, Y. Kosuga, A. Fujisawa, S.-I. Itoh and K. Itoh, End plate biasing experiments in linear magnetized plasmas, NUCLEAR FUSION, 54.0, 11.0, Article No. 114010, 2014.11.
69. Akihide Fujisawa, 恩地 拓己, A. Sanpei, A Prototype diagnostics sytem to detect ultraviolet emission for plasma turbulence, Review of Scientific Instruments, 10.1063/1.4900660, 85, 113502-1-113502-3, 2014.11, A system to detect ultraviolet emissions from plasma is developed for multi-point measurement, the target of which is the imaging of turbulence with a high temporal resolution. A fluorescent glass, which converts ultraviolet emissions to visible light with a wavelength of approximately 540 nm, is utilized in the system. Following the conversion, the fluorescent light is transferred with fibre optics, and is converted to electric signals in a location that is sufficiently distant from an electrically noisy environment around the plasma device. This paper describes a prototype system of this diagnostic method and discusses the spectral analysis obtained using a low-aspect-ratio reversed field pinch RELAX.
70. 稲垣 滋, T. Tokuzawa, T. Kobayashi, 伊藤 早苗, K. Itoh, K. Ida, Akihide Fujisawa, S. Kubo, T. Shimozuma, N. Tamura, N. Kasuya, H. Tsuchiya, Y. Nagayama, Study of non-linear coupling of fluctuations at long distance in LHD, 10.1088/0029-5515/54/11/114014", 54, 114014-1-114014-6, 2014.11, Non-linear coupling between fluctuations at different radial locations is observed on the Large Helical Device (LHD) plasma. The summed bi-coherence between the low frequency macro-scale fluctuation (frequency is f = 2.75 kHz) at ρ = reff/a99 = 0.63 (wher.
71. K. Hanada, N. Yoshida, H. Zushi, K. Nakamura, A. Fujisawa, H. Idei, Y. Nagashima, H. Watanabe, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, O. Watanabe, Y. Takase, A. Fukuyama, O. Mitarai, M. Peng and the QUEST team , Investigation of progression from low to high hydrogen recycling during long duration discharges on a spherical tokamak, QUEST, Proc.25th Fusion Energy Conference (FEC 2014), 2014.10.13-18, St. Petersburg Russian Federation, EX/P1-37, 2014.10, Progression from low (LR) to high recycling (HR) was observed in full non-inductive long duration discharges up to 12 minutes on QUEST. Repetitive transition between LR and HR was induced by periodic gas puffing and the period to recover to LR, rec, was gradually prolonged with the plasma duration. The period, rec, normalized by gas rate has a linear relation to time-integrated H. This indicates hydrogen recycling induced an intentional gas puffing is increasing with time-integrated H which an indicator of hydrogen (H) fluence to the wall. To understand the dependence, deuterium (D) storing capability of the specimen exposed to QUEST plasmas was investigated by implantation of D2+
ions of 1keV and subsequent thermal desorption spectroscopy (TDS) as a post-mortem analysis. A diffusion-trap model, reconstructing the obtained the results of TDS, shows a clear dependence of recycling ratio on fluence and a time evolution of wall-stored H can be reconstructed. The model calculation indicates surface recombination on the deposition layer plays an essential role in QUEST wall behaviour. Wall temperature dependence on the number of injected H to keep density is experimentally investigated and is agreed with the model calculation. This result is quite helpful to execute hot wall experiments on QUEST..
72. Ishiguro, Masaki; Hanada, Kazuaki; Liu, Hiqing; Ogata, Ryota; Isobe, Mitsutaka; Tashima, Saya; Zushi, Hideki; Sato, Khonosuke; Fujisawa, Akihide; Nakamura, Kazuo; Idei, Hiroshi; Sakamoto, Mizuki; Hasegawa, Makoto; Takase, Yuichi; Maekawa, Takashi; Kishimoto, Yasuaki; Mitarai, Osamu; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Investigation of Non-inductive Plasma Current Start-up by RF on QUEST, 15TH INTERNATIONAL CONGRESS ON PLASMA PHYSICS (ICPP2010) & 13TH LATIN AMERICAN WORKSHOP ON PLASMA PHYSICS (LAWPP2010), 10.1088/1742-6596/511/1/012041, 511.0, 0.0, 0.0-0.0, Article No. 012041, 2014.09, Formations of a closed flux surface (CFS) on QUEST are achieved by fully non-inductive current start-up driven by RF, which is 8.2GHz in frequency and more than 40kW in power. It found that appropriate magnetic configuration with positive n-index and reduction of particle recycling was crucial to achieve the non-inductive plasma current start-up (PCS) successfully. Especially the controllability of particle recycling should be improved by wall conditioning based on successive plasma production and wall cleaning with electron cyclotron resonance heating (ECR) plasmas induced by RF in frequency of 2.45GHz..
73. Nakamura, Kazuo; Fujita, H.; Liu, X. L.; Xue, E. B.; Xia, Fan; Mitarai, Osamu; Kurihara, Kenichi; Kawamata, Y.; Sueoka, M.; Hasegawa, Makoto; Tokunaga, Kazutoshi; Zushi, H.; Hanada, K.; Fujisawa, A.; Matsuoka, K.; Idei, H.; Nagashima, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Araki, Kuniaki; Fukuyama, A., Shape Reconstruction of RF-Driven Divertor Plasma on QUEST, IEEE TRANSACTIONS ON PLASMA SCIENCE, 10.1109/TPS.2014.2341616, 42.0, 9.0, 2309.0-2312.0, 0.0, 2014.09, In the present RF-driven plasma with a lot of high-energy electrons, there may be anisotropic plasma pressure, which makes the usual equilibrium analysis difficult, but the Cauchy condition surface method can reconstruct the plasma shape precisely regardless of the anisotropy. In addition, the plasma current effect in the open magnetic surfaces outside of the closed magnetic surfaces is considered in the RF-driven divertor plasma. In the reconstruction process, singular value (SV) decomposition is used and optimal criterion function for generalized cross validation is estimated concerning truncation or reduction of the small-SV components..
74. Kobayashi, T.; Itoh, K.; Ido, T.; Kamiya, K.; Itoh, S. -I.; Miura, Y.; Nagashima, Y.; Fujisawa, A.; Inagaki, S.; Ida, K.; Kasuya, N.; Hoshino, K., Dynamics of edge limit cycle oscillation in the JFT-2M Tokamak, NUCLEAR FUSION, 10.1088/0029-5515/54/7/073017, 54.0, 7.0, Article No. 073017, 2014.07, In the JFT-2M tokamak (JFT standing for JAERI Fusion Torus), the limit cycle oscillation (LCO), together with several variables, i.e., the electrostatic potential, radial electric field, electron density, turbulence intensity, and D-alpha emission from the divertor region, is observed before the L-to-H transition. The spatiotemporal dynamics of the LCO is analysed in detail. Zonal flows are not seen, while modulation is observed in the edge-localized poloidal flow and density gradient. Modulation is also seen in the Reynolds stress, caused by that in the turbulence intensity and turbulence wavenumber. However, flow acceleration cannot be explained by the modulation in the Reynolds stress. Rapid inward propagation is also observed for the density gradient and turbulence packet. The characteristics of the propagation are verified by means of turbulence spreading theory and diffusion theory..
75. Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Ishiguro, M.; Tashima, S.; Liu, H. Q.; Mishra, K.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A.; Nagashima, Y.; Matsuoka, K., Role of stochasticity in turbulence and convective intermittent transport at the scrape off layer of Ohmic plasma in QUEST, PHYSICS OF PLASMAS, 10.1063/1.4890359, 21.0, 7.0, 0.0-0.0, 072311, 2014.07, Statistical features of fluctuations are investigated using the fast camera imaging technique in the scrape of layer (SOL) of electron cyclotron resonance heated Ohmic plasma. Fluctuations in the SOL towards low field side are dominated by coherent convective structures (blobs). Two dimensional structures of the higher order moments (skewness s and kurtosis k) representing the shape of probability density function (PDF) are studied. s and k are seen to be functions of the magnetic field lines. s and k are consistently higher towards the bottom half of the vessel in the SOL showing the blob trajectory along the field lines from the top towards bottom of the vessel. Parabolic relation (k = As-2 + C) is observed between s and k near the plasma boundary, featuring steep density gradient region and at the far SOL. The coefficient A, obtained experimentally, indicates a shift of prominence from pure drift-wave instabilities towards fully developed turbulence. Numerical coefficients characterizing the Pearson system are derived which demonstrates the progressive deviation of the PDF from Gaussian towards gamma from the density gradient region, towards the far SOL. Based on a simple stochastic differential equation, a direct correspondence between the multiplicative noise amplitude, increased intermittency, and hence change in PDF is discussed. (C) 2014 AIP Publishing LLC..
76. Kishore Mishra, Hiroshi Idei, hideki zushi, K. Nagata, R. Akimoto, M. K. Yamamoto, Kazuaki Hanada, makoto hasegawa, Kazuo Nakamura, Akihide Fujisawa, Yoshihiko Nagashima, S. Banerjee, 恩地 拓己, KUZMIN ARSENIY ALEKSANDROVI, Thermal imaging of plasma with a phased array antenna in QUEST, REVIEW OF SCIENTIFIC INSTRUMENTS, 85.0, Article No. 11E808-4, 2014.07.
77. Kishore MISHRA, Hideki ZUSHI, Hiroshi IDEI, Saya TASHIMA, Santanu BANERJEE, Makoto HASEGAWA, Kazuaki HANADA, Kazuo NAKAMURA, Akihide FUJISAWA, Yoshihiko NAGASHIMA, Keisuke MATSUOKA, Arseny KUZMIN, Takumi ONCHI and QUEST Team, Analytical Solution of High βp Equilibria with Natural Inboard Poloidal Null Configuration Obtained in the Spherical Tokamak QUEST, Plasma and Fusion Research, 9.0, RA, Article No. 3402093, 2014.06.
78. K. Hanada, H. Zushi, N. Yoshida, M. Hasegawa, K. Mishra, Kuzumina, K. Nakamura, A. Fujisawa, H. Idei, Y. Nagashima, O. Watanabe, T. Onchi, H. Watanabe, K. Tokunaga, A. Higashijima, S. Kawasaki, H. Nakashima, Y. Takase, A. Fukuyama, O. Mitarai, T. Maekawa and M. Peng, Particle balance in long duration RF driven plasmas on QUEST, 21st International Conference on Plasma Surface Interactions 2014, 2014.06.
79. Akihide Fujisawa, Turbulence in Toroidal Plasma, Proceedings of the 12th Asia Pacific Physics Conference, Article No. 015005, 2014.04, A new paradigm for plasma turbulence has been made; plasma turbulence is regarded as nonlinear system of drift waves and their generated structures, zonal flows, streamers, and large scale modes. New paradigm provides ways to clarify unsolved problems in magnetically confined plasma, for example, confinement improvement, nonlocal transport, isotope effect, and so on. Identification of these structures should contribute to establishing the first principle laws of transport. Full scale measurement covering the whole plasma is essential for further understanding of plasma turbulence in laboratory experiments. Special toroidal device should be made for further physical understanding of turbulence..
80. Shigeru INAGAKI, Yudai MIWA, Tatsuya KOBAYASHI, Takuma YAMADA, Yoshihiko NAGASHIMA, Tomohiro MITSUZONO, Hiromitsu FUJINO, Makoto SASAKI, Naohiro KASUYA, Maxime LESUR, Yusuke KOSUGA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Identification of Quasi-Periodic Nonlinear Waveforms in Turbulent Plasmas, Plasma and Fusion Research, 9.0, RC, 2.0, Article No. 1201016, 2014.03, A new method is presented for identifying waveforms of fluctuations in turbulent plasmas. The method is based on heartbeat analysis in which the convolution of a waveform is obtained by employing the phase tracking method. Phase tracking is performed by correlating raw time-series data with a template waveform; the template is evaluated through iteration procedure. The method is applied to fluctuations in a PANTA plasma, and the nonlinear waveform and its distribution of periods are obtained..
81. Santanu Banerjee, H. Zushi, N. Nishino, Y. Mahira, K. Nagaoka, K. Mishra, S. Tashima, Y. Nagashima, K. Hanada, K. Nakamura, H. Idei, M. Hasegawa, A. Fujisawa, K. Matsuoka, Scrape Off Layer Flow Characteristics in the Spherical Tokamak QUEST, Proceedings of the 12th Asia Pacific Physics Conference, JPS Conf. Proc. ,015036 (2014), 2014.03.
82. Tashima, Saya; Zushi, H.; Isobe, M.; Hanada, K.; Idei, H.; Nakamura, K.; Fujisawa, A.; Matsuoka, K.; Hasegawa, M.; Nagashima, Y.; Okamura, S.; Banerjee, S.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Role of energetic electrons during current ramp-up and production of high poloidal beta plasma in non-inductive current drive on QUEST, NUCLEAR FUSION, 10.1088/0029-5515/54/2/023010, 54.0, 2.0, 0.0-0.0, 023010, 2014.02, A scenario for non-inductive current ramp-up has been demonstrated using electron cyclotron waves in the spherical tokamak QUEST. The configuration was characterized by a high toroidal magnetic mirror ratio of 2 and a steady vertical magnetic field of more than 10% of the toroidal magnetic field. The generation and confinement of energetic electrons having energy greater than 10 keV were studied using hard x-rays. Because of the energetic electron pressure, a natural divertor formed with an inboard poloidal field null at the high poloidal beta (approximately 3-4)..
83. Kimitaka ITOH, Sanae-I. ITOH and Akihide FUJISAWA, An Assessment of Limit Cycle Oscillation Dynamics Prior to L-H Transition, Plasma and Fusion Research, 8.0, Rev, 11.0, Article No. 1102168, 2013.12, In this article, experimental observations of limit cycle oscillations (LCO) that precede L-to-H transition are discussed. Issues are: (1) the existence of zonal flows, (2) spatio-temporal evolutions of turbulence intensity, and (3) periodic generations/decays of mean radial electric field and density. The role of Reynolds stress to accelerate the LCO flow is also addressed. The propagation of changes of the density gradient and turbulence amplitude into the core is commented. Varieties in experimental reports on these issues are explained, and possible origins of different interpretations are discussed. Problem definitions for the future research for resolution are presented..
84. Shigeru INAGAKI, Sanae-I. ITOH, Kimitaka ITOH, Naohiro KASUYA, Tatsuya KOBAYASHI, Akihide FUJISAWA, Tokihiko TOKUZAWA, Katsumi IDA, Shin KUBO, Takashi SHIMOZUMA, Naoki TAMURA, Hayato TSUCHIYA, Yoshio NAGAYAMA, Kazuo KAWAHATA, Hiroshi YAMADA, Akio KOMORI and LHD Experiment Group, Higher Harmonics in a Perturbative Transport Experiment, Plasma and Fusion Research, 8.0, RC, 2.0, Article No. 1202173, 2013.12, We have used the convolution method to obtain higher harmonics of the temperature perturbation in a heating modulation experiment on LHD plasma. In comparison with predictions based on the diffusive model, amplitudes of higher harmonics (such as the seventh) decayed much more slowly as they propagated radially. Changes in the time derivative of temperature at the onset and turning-off of heating power remained much sharper after radial propagation than those predicted by the diffusion model..
85. Shigeru INAGAKI, Kimitaka ITOH, Takuma YAMADA, Sanae-I. ITOH, Tokihiko TOKUZAWA, Akihide FUJISAWA, Naohiro KASUYA, Makoto SASAKI, Yoshihiko NAGASHIMA and Hiroyuki ARAKAWA, Measurement of Dynamical Density Profiles Using a Microwave Frequency Comb Reflectometer, Plasma and Fusion Research, 8.0, RC, 2.0, Article No. 1201171, 2013.12, We propose the use of a microwave comb for measuring the density profile as a continuous function of radius with high temporal resolution. The analysis focuses on phase-sensitive convolution of the reflected waves: convolution of pulses can eliminate statistical noise. The time resolution for constructing the density profile is also discussed..
86. Shigeru INAGAKI, Tokihiko TOKUZAWA, Tatsuya KOBAYASHI, Sanae-I. ITOH, Kimitaka ITOH, Katsumi IDA, Shin KUBO, Takashi SHIMOZUMA, Naoki TAMURA, Akihide FUJISAWA, Naohiro KASUYA, Hayato TSUCHIYA, Yoshio NAGAYAMA, Kazuo KAWAHATA, Hiroshi YAMADA, Akio KOMORI and LHD Experiment Group, New Method of Analysis for Dynamical Transport, Plasma and Fusion Research, 8.0, RC, 2.0, Article No. 1202172, 2013.12, By employing a new method for studying dynamical transport, hysteresis in the flux-gradient relation was recently discovered for modulated heating. In this paper, the new method is compared to the conventional heat-pulse propagation method. We also demonstrate integration of results from the new method with the power balance thermal conductivity..
87. Zhao, K. J.; Cheng, J.; Diamond, P. H.; Dong, J. Q.; Yan, L. W.; Hong, W. Y.; Xu, M.; Tynan, G.; Miki, K.; Huang, Z. H.; Itoh, K.; Itoh, S-I; Fujisawa, A.; Nagashima, Y.; Inagaki, S.; Wang, Z. X.; Wei, L.; Song, X. M.; Lei, G. J.; Li, Q.; Ji, X. Q.; Liu, Yi; Yang, Q. W.; Ding, X. T.; Duan, X. R., Sawtooth-triggered limit-cycle oscillations and I-phase in the HL-2A tokamak, NUCLEAR FUSION, 10.1088/0029-5515/53/12/123015, 53.0, 12.0, 0.0-0.0, 123015, 2013.12, Transitions between low (L-mode) and intermediate (I-phase) confinement regimes triggered by sawteeth are investigated using multiple Langmuir probe arrays in the edge plasmas of the HL-2A tokamak. The I-phase is characterized by limit-cycle oscillations (LCOs). Repeated L-I-L transitions induced by sawtooth heat pulses are also observed. Statistical analyses show that the delay time of the L-I transition relative to sawtooth crashes is less than similar to 1 ms. The intensity of turbulence bursts in the I-phase is stronger than those observed in L-mode plasmas. Measurements are consistent with zonal flow reducing turbulence intensity in the frequency band similar to 20-100 kHz, while the LCO turbulence of frequency higher than 100 kHz has more power than that in the L-mode. The analyses of time-resolved power transfers between turbulence and zonal flows suggest that power transfers exist between turbulence and zonal flows. The direction of the power transfers is from turbulence into geodesic acoustic modes in ohmic plasmas..
88. Inagaki, S.; Tokuzawa, T.; Tamura, N.; Itoh, S. -I.; Kobayashi, T.; Ida, K.; Shimozuma, T.; Kubo, S.; Tanaka, K.; Ido, T.; Shimizu, A.; Tsuchiya, H.; Kasuya, N.; Nagayama, Y.; Kawahata, K.; Sudo, S.; Yamada, H.; Fujisawa, A.; Itoh, K., How is turbulence intensity determined by macroscopic variables in a toroidal plasma?, NUCLEAR FUSION, 10.1088/0029-5515/53/11/113006, 53.0, 11.0, 0.0-0.0, Article No. 113006, 2013.11, We report observations of the dynamic response of micro-fluctuations and turbulent flux to a low-frequency heating power modulation in the Large Helical Device. The responses of heat flux and micro-fluctuation intensity differ from that of the change in temperature gradient. This result violates the local transport model, where turbulence is determined by the local temperature gradient. A new relationship between flux, gradient and turbulence is found. In addition to the temperature gradient, the heating rate is proposed as a new, direct controlling parameter of turbulence to explain the fast response of turbulence against periodic modulation of heating power..
89. Hasegawa, M.; Nakamura, K.; Zushi, H.; Hanada, K.; Fujisawa, A.; Matsuoka, K.; Mitarai, O.; Idei, H.; Nagashima, Y.; Tokunaga, K.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Development of plasma control system for divertor configuration on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2013.03.035, 88.0, 6.0, 1074.0-1077.0, 0.0, 2013.10, A plasma control system to sustain divertor configurations is developed on QUEST (Q-shu university experiment with steady-state spherical tokamak). Magnetic fluxes are numerically integrated at 100 kHz using FPGA (Field-Programmable Gate Array) modules and transferred to a main calculation loop at 4 kHz. With these signals, plasma shapes are identified in real time at 2 kHz under the assumption that the plasma current can be represented as one filament current. This calculation is done in another calculation loop in parallel by taking advantage of a multi-core processor of the plasma control system. The inside and outside plasma edge positions are controlled to their target positions using PID (proportional-integral-derivative) control loops. Whereas the outside edge position can not be controlled by the outer PF coil current, the inside edge position can be controlled by the inner PF coil current. (C) 2013 Elsevier B.V. All rights reserved..
90. Kishore, Mishra; Zushi, H; Idei, H; Tashima, S; Banerjee, S; Hasegawa, M; Hanada, K; Nakamura, K; Fujisawa, A; Nagashima, Y; , 28pKB-2 On formation of a natural inboard separatrix in ECW heated Ohmic plasma on the spherical tokamak QUEST, 日本物理学会講演概要集, 68.0, 2.0, 208.0, 2013.09.
91. Yudai MIWA, Naohiro KASUYA, Makoto SASAKI, Shigeru INAGAKI, Kimitaka ITOH, Masatoshi YAGI, Akihide FUJISAWA, Yoshihiko NAGASHIMA, Maxime LESUR, Tatsuya KOBAYASHI, Soutarou YAMADA, Tetsuo YAMASHITA, Satoshi OTSUBO, Shinsuke KAKIGAWA, Tomohiro MITSUZONO, Hirofumi FUJINO and Sanae-I. ITOH, Evaluation of Excitation Conditions of ITG Modes in the PANTA, Plasma and Fusion Research, 8.0, RA, 5.0, Article No. 2403133, 2013.09, To study the nonlinear saturation mechanism in turbulent plasmas, we plan to obseve ion temperature gradient (ITG) modes in the Plasma Assembly for Nonlinear Turbulence Analysis (PANTA). Linear growth rates of ITG modes in the linear device are analyzed to determine their excitation conditions using a three-field fluid model to describe the ion motion. Parameter scans of the linear growth rate show the threshold for ITG mode excitation, and the typical plasma parameters of the PANTA are found in the unstable domain..
92. Saya TASHIMA, Hideki ZUSHI, Mitsutaka ISOBE, Hiroshi IDEI, Shoichi OKAMURA, Kazuaki HANADA, Kazuo NAKAMURA, Akihide FUJISAWA, Keisuke MATSUOKA, Makoto HASEGAWA, Yoshihiko NAGASHIMA, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and QUEST Team, Non-Inductive Current Drive by EC Waves in an Inboard Poloidal Magnetic Field Null Configuration on the Spherical Tokamak QUEST, Plasma and Fusion Research, 8.0, RA, 5.0, Article No. 2402118, 2013.09, To investigate the effects of confinement of fast electrons on poloidal beta equilibrium, experiments under different toroidal magnetic mirror ratios, MOMFC, were performed in electron cyclotron heated plasma in the spherical tokamak QUEST. The proportional constants of the relation between plasma current and vertical magnetic fields decreased with increase in MOMFC. The poloidal field null point appeared in the chamber for MOMFC > 1.8 at a plasma current value of ∼15 kA. Poloidal beta and temperature of hard X-rays increased with MOMFC. This suggests that high poloidal beta equilibrium plasma is produced by better confinement of energetic trapped particles..
93. Shigeru Inagaki, Akihide Fujisawa, Naohiro Kasuya, Sanae Itoh, Kimitaka Itoh, Measurement of Dynamical Density Profiles Using a Microwave Frequency Comb Reflectometer, Plasma and Fusion Research, 8.0, RC, 2.0, Article No. 1201171, 2013.08.
94. Zhao, K. J.; Dong, J. Q.; Yan, L. W.; Diamond, P. H.; Cheng, J.; Hong, W. Y.; Huang, Z. H.; Xu, M.; Tynan, G. R.; Itoh, K.; Itoh, S. -I.; Fujisawa, A.; Nagashima, Y.; Inagaki, S.; Wang, Z. X.; Wei, L.; Li, Q.; Ji, X. Q.; Huang, Y.; Liu, Yi.; Zhou, J.; Song, X. M.; Yang, Q. W.; Ding, X. T.; Duan, X. R., Spatial structures and interaction of multiple sheared flow populations in tokamak edge turbulence, NUCLEAR FUSION, 10.1088/0029-5515/53/8/083011, 53.0, 8.0, 0.0-0.0, 083011, 2013.08, The radial structures of multiple sheared flow populations and fluctuations are simultaneously measured using combinations of Langmuir probe arrays in the edge plasmas of the HL-2A tokamak with ohmic and electron cyclotron resonance heating (ECRH). The maximum of geodesic acoustic mode (GAM) amplitude locates at similar to 2-3 cm inside the last close flux surface (LCFS). The low-frequency zonal flow (LFZF) and GAM tend to coexist in the inner region. The dependences of the amplitudes of the multiple sheared flows and turbulence on ECRH heating power are also investigated. The measured turbulent Reynolds stresses are shown to be strongly correlated with the sheared flows, as predicted by theory. The turbulence is modulated at the each frequency of the multiple sheared flows simultaneously, and the particle fluxes induced by the turbulence are significantly reduced near the LCFS and in the GAM peaking region. The analyses also show that the spatial structures of the turbulent envelopes at the LFZF and GAM frequencies are similar to those observed in LFZF and GAM..
95. Santanu BANERJEE, Hideki ZUSHI, Nobuhiro NISHINO, Yoshihiko NAGASHIMA, Kazuaki HANADA, Saya TASHIMA, Tsubasa INOUE, Kazuo NAKAMURA, Hiroshi IDEI, Makoto HASEGAWA, Akihide FUJISAWA and Keisuke MATSUOKA, Turbulence Velocimetry of Tangential Fast Imaging Data on QUEST, Plasma and Fusion Research, 8.0, RA, 4.0, Article No. 2402098, 2013.08, A particle image velocimetry technique based on orthogonal dynamic programming is developed to measure the time resolved flow field of the fluctuating structures at the plasma edge and scrape off layer. This non-intrusive technique can provide two dimensional velocity fields at high spatial and temporal resolution from a fast framing image sequence and hence can provide better insights in plasma flow as compared to conventional probe measurements. Applicability of the technique is tested with simulated image pairs. Finally, it is applied to tangential fast visible images of QUEST as a test case to estimate the scrape off layer flow in Ohmic and ECRH driven plasma discharges..
96. Kishore Mishra, Hiroshi Idei, Hideki Zushi, Saya Tashima, Santanu Banerjee, Makoto Hasegawa, Kazuaki Hanada, Kazuo Nakamura, Akihide Fujisawa, Keisuke Matsuoka, Yoshihiko Nagashima, S. Kawasaki, A. Higashijima, H. Nakashima, and Quest Group, Characteristics of High Poloidal Beta (β p) Plasma Formed by Electron Cyclotron Waves in Spherical Tokamak QUEST, Proceedings of the 12th Asia Pacific Physics Conference (APPC12), 1.0, 5.0, Article No. 015031, 2013.07.
97. Liu, H. Q.; Hanada, K.; Nishino, N.; Ogata, R.; Ishiguro, M.; Gao, X.; Zushi, H.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M., Cross-field motion of plasma blob-filaments and related particle flux in an open magnetic field line configuration on QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2013.01.106, 438.0, S513-S517, 2013.07, Blob-filaments have been observed by combined measurement with a fast camera and a movable Langmuir probe in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. Blob-filaments extended along field lines do correspond to over-dense plasma structures and propagated across the field lines to the outer wall. The radial velocity of the blob structure, Vb, was obtained by three methods and was dominantly driven by the E x B force. The radial velocity, size of the blob showed good agreements with the results obtained by sheath-connected interchange theoretical model. Vb corresponds to roughly 0.02-0.07 of the local sound speed (Cs) in QUEST. The higher moments (skewness S and kurtosis K) representing the shape of PDF of density fluctuation are studied. Their least squares fitting with quadratic polynomial is K = (1.60 +/- 0.27) S-2 - (0.46 +/- 0.20). The larger blob structures, occurring only 10% of the time, can carry more than 60% loss of the entire radial particle flux. (C) 2013 Elsevier B.V. All rights reserved..
98. NAKAMURA Kazuo, FUJITA Hiroki, LIU Xiaolong, XUE Erbing, MITARAI Osamu, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, Quaternion Concept in Matrix Converter Design for Feedback Stabilization by Magnetic Field Coil, Proc. International Conference on Electrical Engineering (ICEE 2013),Xiamen,July 2013, S7-02,FP0393, 2013.07.
99. Kobayashi, T.; Itoh, K.; Ido, T.; Kamiya, K.; Itoh, S. -I.; Miura, Y.; Nagashima, Y.; Fujisawa, A.; Inagaki, S.; Ida, K.; Hoshino, K., Spatiotemporal Structures of Edge Limit-Cycle Oscillation before L-to-H Transition in the JFT-2M Tokamak, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.111.035002, 111.0, 3.0, 0.0-0.0, Article No. 035002, 2013.07, In this Letter, we report analyses of spatiotemporal dynamics of turbulence and structure in the limit-cycle oscillation (LCO) that precedes an L-to-H transition. Zonal flows are not observed during LCO, and the oscillation is the periodic generations or decays of barrier with edge-localized mean flow. Oscillatory Reynolds stress is found to be too small to accelerate the LCO flow, by considering the dielectric constant in magnetized toroidal plasmas. Propagation of changes of the density gradient and turbulence amplitude into the core is also observed..
100. NAKAMURA Kazuo, FUJITA Hiroki, LIU Xiaolong, XUE Erbing, XIA Fan, MITARAI Osamu, KURIHARA Kenichi, KAWAMATA Yoichi, SUEOKA Michiharu, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, SHAPE RECONSTRUCTION OF RF-DRIVEN DIVERTOR PLASMA ON QUEST , Proc. Third Meeting for A3 Foresight Program Workshop on Critical Physics Issues Specific to Steady State Sustainment of High-Performance Plasmas,19-24 May 2013,Beijing,China,NIFS-PROC-95, 19-24 May 2013,Beijing,China,NIFS-PROC-95,48-55,2013.12., 2013.05.
101. Teplova (Kosolapova), N.; Itoh, K.; Itoh, S-I; Gusakov, E.; Heuraux, S.; Inagaki, S.; Sasaki, M.; Kobayashi, T.; Nagashima, Y.; Oldenbuerger, S.; Fujisawa, A., On turbulence-correlation analysis based on correlation reflectometry, PHYSICA SCRIPTA, 10.1088/0031-8949/87/04/045502, 87.0, 4.0, 0.0-0.0, Article No. 045502, 2013.04, Drift wave micro-turbulence is the main source of anomalous transport in a tokamak. Correlation reflectometry is a powerful diagnostic tool which provides information on plasma turbulence and subsequently on underlying instability. In this paper, theoretical expressions for the analysis of radial correlation reflectometry (RCR) data are derived. Integral kernels, which convert the correlation function of two microwave reflectometry signals into a correlation function of plasma turbulence and inverse, are discussed. The analytical expression and the method of combining the RCR diagnostic and another local density fluctuation (e.g. Doppler enhanced scattering or heavy ion beam probe) is proposed. The correlation between reflectometry signals and those from other local fluctuation measurements is analysed. The long-range tail of the correlation decays much more gradually than the turbulence correlation, however, it decays faster than that of two microwave reflectometry signals. The way to calculate turbulence wave number spectrum for this case is also proposed..
102. Takuma YAMADA, Makoto SASAKI, Naohiro KASUYA, Yoshihiko NAGASHIMA, Shigeru INAGAKI, Tatsuya KOBAYASHI, Masatoshi YAGI, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Streamer Structures in Experiment and Modeling, Plasma and Fusion Research, 8.0, RA, 5.0, Article No. 2401022, 2013.04, Validation of modeling in meso-scale structure formation is undergoing by using multi-channel probe measurements and advanced analyzing techniques such as bispectrum. Study of meso-scale structures including streamers is important for understanding anomalous transports in magnetized plasmas. A streamer structure and its mediator mode were observed in the Large Mirror Device-Upgrade linear plasma. The mediator mode nonlinearly coupled with many other drift wave modes and generated a streamer structure by phase locking. The radial biphase profiles indicating the phase locking showed the radial elongation of the streamer structure. Modes having similar characteristics to the mediator were also found in a theoretical work based on the Hasegawa-Mima model and a numerical simulation code..
103. Liu Xiaolong, Kazuo Nakamura, Tatsuya Yoshisue, Osamu Mitarai, Makoto Hasegawa, Kazutoshi Tokunaga, Xue Erbing, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Kuniaki Araki, H∞ Loop Shaping Control for Plasma Vertical Position Instability on QUEST, PLASMA SCIENCE & TECHNOLOGY, 15.0, 3.0, 295.0, 2013.03, QUEST has a divertor configuration with a high and a negative n-index, and the problem of plasma vertical position instability control in QUEST is still under extensive study for achieving high efficiency plasma. The instability we considered is that the toroidal plasma moves either up or down in the vacuum chamber until it meets the vessel wall and is extinguished. The actively controlled coils (HCU and HCL) outside the vacuum vessel are serially connected in feedback with a measurement of the plasma vertical position to provide stabilizing control. In this work, a robust controller is employed by using the loop synthesis method, and provides robust stability over a wide range of n-index. Moreover, the gain of the robust controller is lower than that of a typical proportional derivative (PD) controller in the operational frequency range; it indicates that the robust controller needs less power consumption than the PD controller does..
104. Liu Xiaolong; Nakamura, Kazuo; Yoshisue, Tatsuya; Mitarai, Osamu; Hasegawa, Makoto; Tokunaga, Kazutoshi; Xue Erbing; Zushi, Hideki; Hanada, Kazuaki; Fujisawa, Akihide; Idei, Hiroshi; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki; Araki, Kuniaki, H-infinity Loop Shaping Control for Plasma Vertical Position Instability on QUEST, PLASMA SCIENCE & TECHNOLOGY, 10.1088/1009-0630/15/3/21, 15.0, 3.0, 295.0-299.0, 0.0, 2013.03, QUEST has a divertor configuration with a high and a negative n-index, and the problem of plasma vertical position instability control in QUEST is still under extensive study for achieving high efficiency plasma. The instability we considered is that the toroidal plasma moves either up or down in the vacuum chamber until it meets the vessel wall and is extinguished. The actively controlled coils (HCU and HCL) outside the vacuum vessel are serially connected in feedback with a measurement of the plasma vertical position to provide stabilizing control. In this work, a robust controller is employed by using the loop synthesis method, and provides robust stability over a wide range of n-index. Moreover, the gain of the robust controller is lower than that of a typical proportional derivative (PD) controller in the operational frequency range; it indicates that the robust controller needs less power consumption than the PD controller does..
105. Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Sharma, S. K.; Honma, H.; Tashima, S.; Inoue, T.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A., Statistical features of coherent structures at increasing magnetic field pitch investigated using fast imaging in QUEST, NUCLEAR FUSION, 10.1088/0029-5515/52/12/123016, 52.0, 12.0, 0.0-0.0, 123016, 2012.12, Fluctuations in slab plasma produced by electron cyclotron waves in an open magnetic configuration with vertical (B-z) and toroidal (B-t) fields are investigated as a function of B-z/B-t (field pitch) using a high speed visible camera in the spherical tokamak QUEST. Higher order moments (skewness s and kurtosis k) of spatio- temporal fluctuations are investigated. Background fluctuations, generation of coherent convective structures (blobs) and their propagation are analysed at the intensity gradient (R-im) and the source- free (essentially vacuum on the low- field side) regions, respectively. Parabolic relation (k = As-2 + C) is observed between s and k on the entire R- Z plane for a wide range of B-z/B-t. Progressive shift from the Gaussian statistics beyond R-im is observed with increasing B-z/B-t. From the moments of the probability density functions, possible location for blob generation is inferred to be R-im. Direct correspondence is observed with the prominence of the blobs and increase in stochastic forces with the increase in field pitch. Distribution of waiting time suggests that the blob generation may be a Poisson process. Accelerated cross field transport is observed for reasonably large-sized blobs..
106. Santanu Banerjee, H. Zushi, N. Nishino, Y. Nagashima, K. Hanada, S. Tashima, T. Inoue, K. Nakamura, H. Idei, M. Hasegawa, A. Fujisawa and K. Matsuoka, Edge turbulence characteristics of the Ohmic-ECRH driven plasma current phase investigated with fast visible imaging in QUEST, Proc. 22nd International Toki Conference November 19- 22,2012, P3-32, 2012.11.
107. Saya TASHIMA, Hideki ZUSHI, Mitsutaka ISOBE, Hiroshi IDEI, Shoichi OKAMURA, Kazuaki HANADA, Kazuo NAKAMURA, Akihide FUJISAWA, Keisuke MATSUOKA, Makoto HASEGAWA, Yoshihiko NAGASHIMA, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and QUEST Team, Non-Inductive Current Drive by EC Waves in an Inboard Poloidal Magnetic Field Null Configuration on the Spherical Tokamak QUEST, Proc. 22nd International Toki Conference November 19- 22, 2012, 2012.11.
108. Kobayashi, T.; Inagaki, S.; Itoh, S-I; Itoh, K.; Oldenbuerger, S.; Fujisawa, A.; Nagashima, Y.; Ida, K.; Tsuchiya, H.; Nagayama, Y.; Kawahata, K.; Yamada, H., Self-nonlinear coupling of long-range temperature fluctuation in Toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/54/11/115004, 54.0, 11.0, 0.0-0.0, 115004, 2012.11, This paper proposes a clever usage of bispectral analysis for extracting or reconstructing a quasi-coherent and quasi-periodic structural evolution of plasma fluctuations. The method has been applied on electron temperature fluctuation signals measured with a multi-point electron cyclotron emission (ECE) radiometer in the Large Helical Device (LHD). The method successfully reconstructs the averaged spatiotemporal evolution of fluctuating coherent structure (Inagaki et al 2011 Phys. Rev. Lett. 107 115001), while the structure is buried in (or comparable in power to) background fluctuations. The bicoherence analysis has found the faint fluctuating structure consisting of a fundamental mode and the harmonic modes from the existence of significant couplings between them. The reconstructed spatiotemporal structure with the proposed method is compared with that obtained with the lock-in (conditional) average. Three cases of spatiotemporal evolution of the non-sinusoidal waveform are presented..
109. Stella OLDENBÜRGER, Kazuya URIU, Tatsuya KOBAYASHI, Shigeru INAGAKI, Makoto SASAKI, Yoshihiko NAGASHIMA, Takuma YAMADA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Configuration of Flows in a Cylindrical Plasma Device, Plasma and Fusion Research, 7.0, RA, 4.0, Article No. 2401146, 4 pages, 2012.10, Ion flow is studied in the cylindrical magnetized Argon plasma of the PANTA device using several experimental methods. Time delay estimation technique (TDE) is used to measure the azimuthal propagation of density fluctuations between two electrostatic probes. Ion flux is also studied in azimuthal and axial direction using a newly installed Mach probe. TDE shows velocity profiles qualitatively consistent with expected drift wave propagation and E × B rotation. The Mach probe shows a maximum azimuthal flow and an axial flow shear close to the maximum density gradient and maximum fluctuation position. Striking differences exist in the detected axial ion flows depending on the discharge parameters. In high neutral pressure conditions reversal of axial ion flow was detected in the outer part of the plasma column. Temporal evolution of flows and fluctuations are compared as a first step to assess interplay between plasma turbulence and flows in the radial, axial and azimuthal directions..
110. Soutaro YAMADA, Shigeru INAGAKI, Stella OLDENBÜRGER, Tatsuya KOBAYASHI, Katsuyuki KAWASHIMA, Noriko OHYAMA, Yuki TOBIMATSU, Hiroyuki ARAKAWA, Yoshihiko NAGASHIMA, Takuma YAMADA, Makoto SASAKI, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Evaluation of Electron Temperature Fluctuations Using a Conditional Technique, Plasma and Fusion Research, 7.0, RA, 3.0, Article No. 2401133, 2012.10, Electron temperature fluctuation amplitude is evaluated with a single probe using conditional sampling technique on the PANTA (linear magnetic configuration device). Electron temperature fluctuations are extracted as a function of floating potential. Normalized temperature fluctuation amplitude of about 15% is observed in low neutral pressure discharge in PANTA..
111. Banerjee, Santanu; Zushi, H.; Nishino, N.; Nagashima, Y.; Hanada, K.; Ishiguro, M.; Ryoukai, T.; Tashima, S.; Inoue, T.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A.; Matsuoka, K., Fast visible imaging and edge turbulence analysis in QUEST, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.4739080, 83.0, 10.0, Article No. 10E524, 2012.10, A fast visible imaging system is installed on the spherical tokamak QUEST to study edge turbulence. The camera uses a complementary metal-oxide semiconductor detector with a maximum resolution of 1024 x 1024 at 7000 frames/s (fps) and can achieve 775 kfps at a resolution of 128 x 24. In this paper, we present the salient features of the system and its application to study edge turbulence in 8.2 GHz ECRH driven slab plasma, without plasma current. Vertical magnetic field (B-z) topology is varied with three sets of poloidal field (PF) coils and the variation in the edge turbulence is investigated as a function of the B-z strength and curvature. Fluctuation amplitude was highest for the shallow PF well. Cross-correlation coefficient shows distinct coherent mode along z direction at the steep density gradient region and it grows with the PF mirror ratio. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739080].
112. H. Zushi; S. Tashima; M. Ishiguro; M. Hasegawa; S. Banerjee; N. Nishino; M. Isobe; K. Hanada; H. Idei; K. Nakamura; A. Fujisawa; Y. Nagashima; K. Matsuoka, S. K. Sharma; H. Liu; K. Toi; T. Maekawa; A. Ejiri; T. Yamaguchi;J. Hiratsuka; Y. Takase; M. Kikuchi; A. Fukuyama; Y. Ueda; O. Mitarai; S. Okamura;, Non-inductive current start-up and plasma equilibrium with an inboard poloidal field null by means of electron cyclotron waves in QUEST, Proc. 24th Int. Conf. on Fusion Energy (San Diego, CA, 2012), (※), 2012.10.
113. T. Kobayashi, Shigeru Inagaki, ITOH INOUE(論文のみ) SANAE, K. Itoh, OLDENBURGER STELLA, Fujisawa Akihide, Nagashima Yoshihiko, K. Ida, H. Tsuchiya, Y. Nagayama, K. Kawahata, H. Yamada, Spatiotemporal dynamic characteristics and self-nonlinear coupling of long-range temperature fluctuation in Toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 54,11, 2012.10.
114. Santanu BANERJEE, H ZUSHI, N NISHINO, Y NAGASHIMA, K HANADA, S TASHIMA, T INOUE, K NAKAMURA, H IDEI, M HASEGAWA, A FUJISAWA, K MATSUOKA, 18aFA-6 Fluctuation characteristics and flow at the SOL of ECRH driven plasma in QUEST, 日本物理学会講演概要集, 67.0, 2.0, 185.0, 2012.09.
115. Santanu BANERJEE, H ZUSHI, N NISHINO, K HANADA, HQ Liu, M ISHIGURO, T RYOUKAI, S TASHIMA, T INOUE, K NAKAMURA, H IDEI, H HASEGAWA, A FUJISAWA, K MATSUOKA, Y NAGASHIMA, 25pYG-5 Effect of poloidal magnetic field curvature variations on the edge turbulence of 8.2 GHz slab plasma in QUEST, 日本物理学会講演概要集, 67.0, 1.0, 271.0, 2012.09.
116. Hiroshi IDEI, Hideki ZUSHI, Kazuaki HANADA, Evgeniya KALINNIKOVA, Kazuo NAKAMURA, Akihide FUJISAWA, Yoshihiko NAGASHIMA, Makoto HASEGAWA, Keisuke MATSUOKA, Tsuyoshi KARIYA, Tsuyoshi IMAI, Ryutaro MINAMI, Naoaki YOSHIDA, Mizuki SAKAMOTO, Hideo WATANABE, Kazutoshi TOKUNAGA, Akira EJIRI, Masatsugu SAKAGUCHI, Masaki ISHIGURO, Saya TASHIMA, Atsushi FUKUYAMA, Hiroe IGAMI, Shin KUBO, Mitsutaka ISOBE, Kenichi NAGAOKA, Hideya NAKANISHI, Nobuhiro NISHINO, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA, Yuichi TAKASE, Takashi MAEKAWA, Osamu MITARAI, Mitsuru KIKUCHI and Kazuo TOI, ECW/EBW Heating and Current Drive Experiment Results and Prospects for CW Operation in QUEST, Plasma and Fusion Research, 7.0, RA, Article No. 2402112, 2012.09, A CW phased-array antenna system for electron cyclotron/Bernstein wave heating and current drive (ECWH/CD, EBWH/CD) experiments was developed in the QUEST. The antenna was designed to excite an elliptically polarized pure O-mode wave in oblique injection for the O-X-B mode conversion scenario, and its good performance was confirmed at a high power level. Long pulse discharges with a plasma current of 10 kA and 15 kA were non-inductively attained for 37 s and 20 s, respectively, with only radio frequency (RF) power. Divertor configurations were also obtained in the RF-sustained plasmas. A new operational window for sustained plasma current was observed in the high-density plasma with a higher RF incident power. Two new heating and current drive systems with an 8.56 GHz klystron and a 28 GHz gyrotron are being prepared to conduct CW EBWH/CD experiments in the high-density plasma..
117. H. Idei, H. Zushi, K. Hanada, E. Kalinnikova, M. Sakaguchi, T. Itado, K. Nakamura, A. Fujisawa, Y. Nagashima, M. Hasegawa, K. Matsuoka, A. Fukuyama, S. Tashima, H. Watanabe, N. Yoshida, K. Tokunaga, A. Ejiri, H. Igami, S. Kubo, K. Toi, M . Isobe, K. Nagaoka, H. Nakanishi, N. Nishino, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Ueda, M. Kikuchi, T. Fujita, O. Mitarai, T. Maekawa and Y. Takase, Electron Bernstein Wave Heating and Current Drive Effects in QUEST, FEC 2012: 24. IAEA Fusion Energy Conference; San Diego, CA (United States); 8-13 Oct 2012, 217.0, EX/P6-17, 2012.09.
118. Itoh, K.; Itoh, S-I; Inagaki, S.; Kobayashi, T.; Fujisawa, A.; Nagashima, Y.; Urger, S. Oldenb; Ida, K.; Tokuzawa, T.; Nagayama, Y.; Kawahata, K.; Yamada, H., On influences of long-range fluctuations on transport in Large Helical Device plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/54/9/095016, 54.0, 9.0, 0.0-0.0, 095016, 2012.09, The competing effects of the long-range fluctuation, which has been found on the Large Helical Device (Inagaki et al 2011 Phys. Rev. Lett. 107 115001), on the net turbulent transport are discussed. The transport, which is driven directly by this mode, is evaluated. Then, the associated reduction of fluctuations in the range of drift wave turbulence is analyzed, by employing the predator-prey model. The transport driven by microscopic turbulence is reduced by the appearance of long-range fluctuations. Comparing these two competing processes, the condition is derived for the net transport to be reduced by the appearance of this long-range fluctuation. In addition, the experimental observations of microscopic fluctuations are discussed. The reduction of high-frequency fluctuations occurs in conjunction with the long-range fluctuations..
119. Alexander V. MELNIKOV, Carlos HIDALGO, Takeshi IDO, Akihiro SHIMIZU, Akihide FUJISAWA, Konstantin S. DYABILIN and Sergey E. LYSENKO, Plasma Potential in Toroidal Devices: T-10, TJ-II, CHS and LHD, Plasma and Fusion Research, 7.0, RA, 4.0, Article No. 2402114, 4 pages, 2012.09, Direct measurements of the electric potential φ, using the Heavy Ion Beam Probing, have been undertaken in the T-10 tokamak, and in the helical devices with various magnetic topology: TJ-II, CHS and LHD. L-mode plasmas were considered. Despite the large differences in machine sizes, heating methods and the topology of the magnetic field, the observed φ shows the striking similarities: (i) Similar magnitudes of Er; (ii) For low densities, ne < 0.5 × 1019 m−3, φ is positive, and an increase in ne is associated with the decrease of positive φ and formation of a negative Er; (iii) For higher densities, ne > (0.5-1)× 1019 m−3 , both φ and Er tends to be negative despite the use of different heating methods: Ohmic and ECR heating in T-10, ECRH and/or NBI in TJ-II, CHS and LHD; (iv) Application of ECRH, causing a rise in Te, results in more positive values for φ and Er. The analysis show that the main features of the φ dependences on the ne and Te agree with neoclassical predictions on the four devices within experimental and simulation precisions..
120. TASHIMA, H ZUSHI, M ISOBE, H IDEI, S OKAMURA, K HANADA, K NAKAMURA, A FUJISAWA, K MATSUOKA, M HASEGAWA, Y NAGASHIMA, M ISHIGURO, S KAWASAKI, H NAKASHIMA, A HIGASHIJIMA, The role of energetic electrons on non-inductive current start-up and formation of an inboard poloidal field null configuration in the spherical tokamak QUEST, 39th EPS Conference & 16th Int. Congress on Plasma Physics, Vol.54 023010 , 2012.08.
121. Makoto Hasegawa, Kazuo Nakamura, Kazutoshi Tokunaga, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, A Plasma Shape Identification with Magnetic Analysis for the Real-time Control on QUEST, IEEJ Transactions on Fundamentals and Materials, 132.0, 7.0, 477.0-484.0, 2012.07, In order to identify plasma shape, there is a way to represent the plasma current profile with several parameters, and adjust these parameters with least-square technique in order for calculated magnetic values to accord with measured ones. Here, the plasma shape parameters such as minor radius, elongation, and triangularity are chosen as the fitting parameters to represent plasma shape more directly, and the applicability to the control of the plasma shape are described by evaluating its calculation time. In order to find minimum of an objective function with least-square technique, two methods are compared, namely a linear approximation method and a downhill simplex method. While high accuracies of the measured magnetic signals are required, the good reproducibility is obtained, and the plasma shape identification can be done within several milliseconds in both methods..
122. Kazuaki Hanada, Hideki Zushi, Hiroshi Idei, Kazuo Nakamura, Masaki Ishiguro, Saya Tashima, Evgeniya Kalinnikova, Mizuki Sakamoto, Makoto Hasegawa, Akihide Fujisawa, Konosuke Sato, Naoaki Yoshida, Hideo Watanabe, Kazutoshi Tokunaga, Yoshihiko Nagashima, Aki Higashijima, Shoji Kawasaki, Hisatoshi Nakashima, Haiqing Liu, Osamu Mitarai, Takashi Maekawa, Atsushi Fukuyama, Yuichi Takase, Jinping Qian, QUEST Experiments Towards Steady State Operation of Spherical Tokamaks, IEEJ Transactions on Fundamentals and Materials, 132.0, 7.0, 490.0-498.0, 2012.07, QUEST計画の大きな目標の一つは、高温プラズマの定常化にかかわる研究である。本論文は、論文は論文は発表時点での長時間維持についての報告(国際球状トカマクワークショップ:平成23年11月於核融合科学研究所)をまとめたものである。特に長時間運転での粒子バランスについてのポイントモデルを用いて、QUESTのパラメータを用いると粒子バランスの定常化に必要な時間が1018秒程度になることを示した。.
123. LIU Xiaolong, YOSHISUE Tatsuya, NAKAMURA Kazuo, XUE Erbing, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, Robust Control on Plasma Vertical Position Instability by a Matrix Converter as Power Supply of QUEST, Proc. International Conference on Electrical Engineering (ICEE 2012),Kanazawa,July 2012 , (※), 2012.07.
124. Santanu Banerjee, Hideki Zushi, Nobuhiro Nishino, Kazuaki Hanada, Sanjeev Kumar Sharma, Tsubasa Inoue, Haiqing Liu, Masaki Ishiguro, Tomofumi Ryokai, Saya Tashima, Kazuo Nakamura, Hiroshi Idei, Makoto Hasegawa, Akihide Fujisawa, Keisuke Matsuoka, Statistical Analysis of the Convective Intermittent Transport at the Edge Region of QUEST, IEEJ Transactions on Fundamentals and Materials, 132.0, 7.0, 545.0-554.0, 2012.07.
125. NAKAMURA Kazuo, YOSHISUE Tatsuya, LIU Xiaolong, XUE Erbing, MITARAI Osamu, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, Three Phase-to-Single Phase Matrix Converter Design for Feedback Stabilization by Magnetic Field Coil, Proc. International Conference on Electrical Engineering (ICEE 2012),Kanazawa,July 2012 , (※), 2012.07.
126. Ishiguro, Masaki; Hanada, Kazuaki; Liu, Haiqing; Zushi, Hideki; Nakamura, Kazuo; Fujisawa, Akihide; Idei, Hiroshi; Nagashima, Yoshihiko; Hasegawa, Makoto; Tashima, Saya; Takase, Yuichi; Kishimoto, Yasuaki; Mitarai, Osamu; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Non-inductive current start-up assisted by energetic electrons in Q-shu University experiment with steady-state spherical tokamak, PHYSICS OF PLASMAS, 10.1063/1.4731700, 19.0, 6.0, Article No. 062508, 2012.06, After intensive discharge cleaning of the chamber wall, non-inductive current start-up experiments have been successfully performed in QUEST in moderate vertical fields of about 1.0-1.5mT with positive n-index. Simultaneously, with increasing plasma current, an asymmetric toroidal flow of energetic electrons was observed and direct measurements of current driven by this asymmetric flow were taken with a newly developed Langmuir probe technique. A numerical study of the energetic electron orbits indicates that the total current is enough to play a dominant role in the formation of a closed flux surface in QUEST. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731700].
127. Tatsuya KOBAYASHI, Shigeru INAGAKI, Stella OLDENBÜRGER, Katsuyuki KAWASHIMA, Noriko OHYAMA, Yuuki TOBIMATSU, Hiroyuki ARAKAWA, Makoto SASAKI, Yoshihiko NAGASHIMA, Takuma YAMADA, Satoru SUGITA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Time Evolution of Power Spectrum Density in Spontaneous Transition in Cylindrical Magnetized Plasma, Plasma and Fusion Research, 7.0, RA, 5.0, Article No. 2401054, 2012.06, Preliminary observation results are reported for a new discharge regime in the Plasma Assembly for Nonlinear Turbulent Analysis (PANTA), where spontaneous transitions in the equilibrium profile and fluctuation spectra occur. Two different states are defined by using the mean density value. Axial and radial profiles are observed for the two states, and large profile changes are found. The spatiotemporal evolution of the transition front is measured. Changes in the fluctuation spectrum are evaluated using conditional average and lock-in average..
128. Oldenbuerger, S.; Inagaki, S.; Kobayashi, T.; Arakawa, H.; Ohyama, N.; Kawashima, K.; Tobimatsu, Y.; Fujisawa, A.; Itoh, K.; Itoh, S-I, Dynamics of particle flux in a cylindrical magnetized plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/54/5/055002, 54.0, 5.0, Article No. 055002, 2012.05, Fluctuation-induced cross-field convective particle flux is studied in the cylindrical magnetized plasma assembly for non-linear turbulence analysis (PANTA). The plasma presents a wave turbulence characterized by a limited number of developing modes. To study the link between mode dynamics and particle transport, frequency-dependent time evolution of transport is obtained by applying complex continuous wavelet decomposition on spatio-temporal data from electrostatic probes. The method is shown to recover transport description consistent with other analysis methods for a weakly turbulent state. For a plasma state featuring a large non-sinusoidal structure, the time evolution of transport on the second harmonic of the main fluctuation shows a slow modulation of azimuthal mode number m = 0 with similarities to a zonal perturbation..
129. Noriko OHYAMA, Akihide FUJISAWA, Shigeru INAGAKI, Yoshihiko NAGASHIMA, Stella OLDENBÜRGER, Tatsuya KOBAYASHI, Katsuyuki KAWASHIMA, Yuuki TOBIMATSU, Tetsuo YAMASHITA, Soutaro YAMADA, Hiroyuki ARAKAWA, Takuma YAMADA, Masatoshi YAGI, Naohiro KASUYA, Makoto SASAKI, Sanae-I. ITOH and Kimitaka ITOH, Observations of Intermittent Structures in the Periphery of a Cylindrical Linear Plasma in PANTA, Plasma and Fusion Research, 7.0, Article No. 1201025 , 2012.05.
130. Noriko OHYAMA, Akihide FUJISAWA, Shigeru INAGAKI, Yoshihiko NAGASHIMA, Stella OLDENBÜRGER, Tatsuya KOBAYASHI, Katsuyuki KAWASHIMA, Yuuki TOBIMATSU, Tetsuo YAMASHITA, Soutaro YAMADA, Hiroyuki ARAKAWA, Takuma YAMADA, Masatoshi YAGI, Naohiro KASUYA, Makoto SASAKI, Sanae-I. ITOH and Kimitaka ITOH, Observations of Intermittent Structures in the Periphery of a Cylindrical Linear Plasma in PANTA, Plasma and Fusion Research, 7.0, RC, 2.0, Article No. 1201025, 2012.04, Intermittent pulse events have been observed in the periphery of the linear cylindrical plasmas produced in Plasma Assembly for Nonlinear Turbulence Analysis (PANTA). A novel combination of 32 azimuthal and 3 radial probes enables us to obtain 32 × 3 = 96 pairs of correlations simultaneously. The two-dimensional (2D) correlation analysis shows that the intermittent structure is well correlated with quasi-periodic bursts inside the plasma, and it reveals that the intermittent pulse is caused by the passage of a radially elongated and azimuthally distorted localized structure rotating in the ion diamagnetic direction..
131. Inagaki, Shigeru; Kobayashi, Tatsuya; Itoh, Kimitaka; Tokuzawa, Tokihiko; Itoh, Sanae-I.; Ida, Katsumi; Tamura, Naoki; Kasuya, Naoyuki; Fujisawa, Akihide; Kubo, Shin; Shimozuma, Takashi; Yagi, Masatoshi; Tanaka, Kenji; Nagayama, Yoshio; Kawahata, Kazuo; Yamada, Hiroshi, Bi-Coherence Analysis of Fluctuations with Long Distance Correlation in Toroidal Plasmas, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.81.034501, 81.0, 3.0, 0.0-0.0, Article No. 034501, 2012.03, Macro-scale temperature fluctuations, which have long radial correlation length (of the order of the plasma radius), have been discovered on Large Helical Device (LHD). In this paper, non-linear coupling between the long-range fluctuations and microscopic fluctuations is investigated using cross bi-coherence analysis. The significant cross bi-coherence between long-range fluctuations and micro-fluctuations is observed in the range of frequency f < 100 kHz, where f is the frequency of microscopic fluctuations. It is found that the squared bi-coherence and bi-phase for this three-wave coupling is weakly dependent on the frequency of microscopic fluctuations. These observations demonstrate that the microscopic fluctuations are coherently interacting with long-range fluctuations..
132. Inagaki, S.; Tamura, N.; Tokuzawa, T.; Ida, K.; Kobayashi, T.; Shimozuma, T.; Kubo, S.; Tsuchiya, H.; Nagayama, Y.; Kawahata, K.; Sudo, S.; Fujisawa, A.; Itoh, K.; Itoh, S. -I., Fluctuations with long-distance correlation in quasi-stationary and transient plasmas of LHD, NUCLEAR FUSION, 10.1088/0029-5515/52/2/023022, 52.0, 2.0, Article No. 023022, 2012.02, Electron temperature fluctuations with long-distance correlation have been discovered in LHD. This paper reports the extended observations recently made on the spatiotemporal structure of the long-range fluctuations both in quasi-stationary and transient plasmas. The detailed characteristics or spatiotemporal characteristics of long-range temperature fluctuations are revealed successfully using correlation analysis. Particularly, the dynamics of the longrange fluctuations is investigated to find that the amplitude of the fluctuations decreased and their radial correlation lengths shortened during the transient phase induced by pellet injection. Temporal changes of radial correlation structure and amplitude of fluctuations at the onset of change in the plasma state are discussed..
133. Sharma, S. K.; Zushi, H.; Yoshida, N.; Watanabe, H.; Osakabe, M.; Takeri, Y.; Hasegawa, M.; Tanabe, T.; Tokunaga, K.; Hanada, K.; Idei, H.; Sakamoto, M.; Nakamura, K.; Fujisawa, A.; Ishiguro, M.; Tashima, S., Analysis of PWI footprint traces and material damage on the first walls of the spherical tokamak QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2011.10.001, 87.0, 1.0, 77.0-86.0, 2012.01, After several non-inductive current startup experimental campaigns in the spherical tokamak QUEST, its metallic first walls have revealed various kinds of damages as a signature of strong plasma wall interaction (PWI). Several types of footprint traces, namely colored regions formed due to material erosion/redeposition, melting of plasma facing components (PFCs) and numerous arc tracks on the chamber walls are recognized. Analysis of the re-deposited materials on collector probes is carried out using Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Redeposition of several impurity materials such as carbon, oxygen and tungsten is identified. The footprint traces are majorly formed on the lower side PFCs, showing a large up/down asymmetry. Both toroidally symmetric and asymmetric footprint traces are formed on the bottoms side divertor plate and the lower part of the outboard side walls, respectively. Localized melting occurred on the outboard side limiters is attributed to the loss of energetic electrons produced via electron cyclotron resonance (ECR) heating. The observed damages are discussed in view of localized PWI, loss of energetic electrons, particle drifts, sputtering, arcing and redeposition of eroded materials. Material analysis and numerically calculated guiding center orbits of the charge particles are used to discuss these damages. (C) 2011 Elsevier B.V. All rights reserved..
134. H. Idei, H. Zushi, K. Hanada, K. Nakamura, A. Fujisawa, M. Hasegawa, N. Yoshida, M. Sakamoto, H. Watanebe, K. Tokunaga, Y. Nagashima, A. Ejiri, M. Sakaguchi, E. Kalinnikova, M. Ishiguro, S. Tashima, A. Fukuyama, H. Igami, S. Kubo, S. K. Sharma, T. Ryokai, H. Q. Liu, M. Isobe, K. Nagaoka, H. Nakanishi, N. Nishino, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai, M. Kikuchi and K. Toi, Electron Cyclotron / Bernstein Wave Heating and Current Drive Experiments using Phased-array Antenna in QUEST, AIP Conference Proceedings (Radio Frequency Power in Plasmas), 1406,473-476, 2011.12.
135. Fujisawa, Akihide, Experimental studies of mesoscale structure and its interactions with microscale waves in plasma turbulence, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/53/12/124015, 53.0, 12.0, Article No. 124015, 2011.12, The modern view of plasma turbulence has been established due to the discovery of zonal flows and other structures which drift-waves generate, and contributes to exploring new manners of understanding turbulence-driven transport and structural formation in magnetized plasmas and astronomic objects. This paper presents the recent development of laboratory experiments, in particular, for drift-wave turbulence which have advanced understanding and have made the paradigm shift. The topics include the discovery of mesoscale structures, such as zonal flows and streamers, the recent development of analyzing techniques to quantify the couplings between different scale structures and methods to elucidate energy transfer direction, and turbulence transport and barrier formation. Finally, future experiments are suggested for establishing the first-principle laws of turbulence transport and structural formation..
136. Ishiguro, Masaki; Hanada, Kazuaki; Liu, Haiqing; Zushi, Hideki; Yoshida, Naoaki; Tokunaga, Tomonori; Nakamura, Kazuo; Fujisawa, Akihide; Idei, Hiroshi; Sakamoto, Mizuki; Hasegawa, Makoto; Tashima, Saya; Takase, Yuichi; Maekawa, Takashi; Kishimoto, Yasuaki; Mitarai, Osamu; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Direct measurement of energetic electron flow in Q-shu University experiment with steady-state spherical tokamak, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.3662204, 82.0, 11.0, Article No. 113509, 2011.11, In magnetized plasmas, the presence of a significant number of energetic electrons has been observed but quantitative characteristics of these electrons are proving difficult to investigate. A Langmuir probe offers a means to provide quantitative measurement of these energetic electrons that takes into account electron emissions (secondary electron emission and electron reflection) from the probe tips and sheath expansion around the probe tips caused by a considerable negative potential. In this paper, these effects are experimentally confirmed and an analytical means to measure energetic electron characteristics are proposed. An analysis of plasmas produced by a high frequency wave is then applied leading to the successful detection of an asymmetric flow of energetic electrons. The estimated electron temperature and current density were approximately 4-5 keV and 2-3 kA/m(2). (C) 2011 American Institute of Physics. [doi:10.1063/1.3662204].
137. Arakawa, H.; Kobayashi, T.; Inagaki, S.; Kasuya, N.; Oldenbuerger, S.; Nagashima, Y.; Yamada, T.; Yagi, M.; Fujisawa, A.; Itoh, K.; Itoh, S-I, Dynamic interaction between a solitary drift wave structure and zonal flows in a linear cylindrical device, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/53/11/115009, 53.0, 11.0, 0.0-0.0, Article No. 115009, 2011.11, A solitary drift wave structure and its quasi-periodic change are discovered in a linear magnetized plasma. Detailed investigations show that the periodic changes are accompanied by an emission of splash, that is, a short lifetime event characterized by much higher frequencies than that of the fundamental drift waves. Dynamic interaction between the solitary wave and zonal flows is found to cause the emission of splashes since the splashes occur in a particular phase of zonal flows. The findings should give a deep insight into the dynamics and structural formation of magnetically confined plasmas and rotating planets, which are governed by drift and Rossby waves, respectively..
138. Xiaolong Liu, Kazuo Nakamura, Tatsuya Yoshisue, Osamu Mitarai, Makoto Hasegawa, Kazutoshi Tokunaga, Erbing Xue, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Kuniaki Araki, Optimal Control on Plasma Vertical Position Instability in QUEST, Proc. 13th Cross Straits Symposium,Kyushu University,Fukuoka,Nov.,2011, 31.0-21.0, 2011.11.
139. Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Liu, H. Q.; Ishiguro, M.; Ryoukai, T.; Tashima, S.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A., Statistical Interpretation of the Density Fluctuations From the High-Speed Visible Images of Edge Turbulence on QUEST, IEEE TRANSACTIONS ON PLASMA SCIENCE, 10.1109/TPS.2011.2163423, 39.0, 11.0, 3006.0-3007.0, 0.0, 2011.11, Edge turbulence has been imaged on QUEST at high temporal resolution (50 kHz) using a fast framing visible camera. Statistical features of fluctuations including blobs are investigated in both open and closed magnetic configurations. Higher order moments of fluctuations including blobs and their mutual relationships are investigated. Close resemblance of the density pdf with Gaussian or beta distributions has earlier been predicted. Hence, an attempt has been made to characterize the density pdf with respect to the Pearson system to ascertain the implications of the stochastic forces..
140. Nakamura, K.; Jiang, Y.; Liu, X. L.; Mitarai, O.; Kurihara, K.; Kawamata, Y.; Sueoka, M.; Hasegawa, M.; Tokunaga, K.; Zushi, H.; Hanada, K.; Fujisawa, A.; Sakamoto, M.; Idei, H.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Araki, K., Eddy current-adjusted plasma shape reconstruction by Cauchy condition surface method on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2011.04.045, 86.0, 6.0, 1080.0-1084.0, 2011.10, CCS (Cauchy Condition Surface) method is a numerical approach to reproduce plasma shape, which has good precision in conventional tokamaks. In order to apply it in plasma shape reproduction of ST (Spherical Tokamak). the calculation precision of the CCS method in a spherical tokamak CPD (Compact PWI experimental Device)(B(t) = 0.25 T, R = 0.3 m, a = 0.2 m) has been analyzed. The precision was confirmed also in ST and decided to be applied to a spherical tokamak QUEST (B(t), = 0.25 T, R = 0.68 m, a = 0.40 m).. In present stage from the magnetic measurement, it is known that the eddy current effect is large in QUEST experiment, and there are no special magnetic measurements for eddy current now, so some proper model should be selected to evaluate the eddy current effect. The eddy current density by not only CS (Center Solenoid) coil but also plasma current is calculated using EDDYCAL (JAEA). The eddy current magnitudes are taken as unknown variables and solved together with plasma shape reconstruction in ohmic discharge and ECCD (Electron Cyclotron Current Drive) discharge. (C) 2011 Elsevier B.V. All rights reserved..
141. Xiaolong LIU, Kazuo NAKAMURA, Yi JIANG, Tatsuya YOSHISUE, Osamu MITARAI, Makoto HASEGAWA, Kazutoshi TOKUNAGA, Hideki ZUSHI, Kazuaki HANADA, Akihide FUJISAWA, Hiroshi IDEI, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and Kuniaki ARAKI, Study of Matrix Converter as a Current-Controlled Power Supply in QUEST Tokamak, Plasma and Fusion Research, 6.0, RA, 5.0, Article No. 2405137, 2011.10, Because QUEST tokamak has a divertor configuration with a higher κ and a negative n-index, a precise power supply with a rapid response is needed to control the vertical position of the plasma. A matrix converter is a direct power conversion device that uses an array of controlled bidirectional switches as the main power elements for creating a variable-output current system. This paper presents a novel three-phase to two-phase topological matrix converter as a proposed power supply that stabilizes the plasma vertical position and achieves unity input power factor. An indirect control strategy in which the matrix converter is split into a virtual rectifier stage and a virtual inverter stage is adopted. In the virtual rectifier stage, the instantaneous active power and reactive power are decoupled on the basis of system equations derived from the DQ transformation; hence, unity power factor is achieved. Space vector pulse width modulation is adopted to determine the switching time of each switch in the virtual rectifier; the output voltage of the virtual rectifier is adjusted by the virtual inverter stage to obtain the desired load current. Theoretical analyses and simulation results are provided to verify its feasibility..
142. SK Sharma, H Zushi, N Yoshida, H Watanabe, M Osakabe, Y Takeiri, M Hasegava, K Tokunaga, K Hanada, H Idei, M Sakamoto, K Nakamura, A Fujisawa, M Ishiguro, S Tashima, Team QUEST, 25pGW-5 Effect of TF ripples on plasma wall interaction and localized damages due to loss of energetic electrons in QUEST, 日本物理学会講演概要集, 66.0, 1.0, 240.0, 67.0,2.0, 2011.09.
143. Santanu Banerjee, H Zushi, N Nishino, K Hanada, H Honma, HQ Liu, M Ishiguro, T Ryoukai, S Tashima, K Nakamura, H Idei, M Hasegawa, A Fujisawa, 26pGW-12 B_Z dependence of the higher order moments of density fluctuations in slab geometry plasma in QUEST, 日本物理学会講演概要集, 66.0, 1.0, 256.0, 2011.09.
144. HQ Liu, K Hanada, N Nishino, R Ogata, M Ishiguro, H Zushi, K Nakamura, A Fujisawa, H Idei, M Hasegawa, 26pGW-13 Experimental observation and Statistical Analysis of Blob-like Structures in QUEST, 日本物理学会講演概要集, 66.0, 1.0, 256.0, 2011.09.
145. Ogata, R.; Hanada, K.; Nishino, N.; Liu, H. Q.; Zushi, H.; Ishiguro, M.; Ikeda, T.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Investigations of the radial propagation of blob-like structure in a non-confined electron cyclotron resonance heated plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak, PHYSICS OF PLASMAS, 10.1063/1.3640494, 18.0, 9.0, 0.0-0.0, Article No. 092306, 2011.09, A study of radial propagation and electric fields induced by charge separation in blob-like structures has been performed in a non-confined cylindrical electron cyclotron resonance heating plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak using a fast-speed camera and a Langmuir probe. The radial propagation of the blob-like structures is found to be driven by E x B drift. Moreover, these blob-like structures were found to have been accelerated, and the property of the measured radial velocities agrees with the previously proposed model [C. Theiler et al., Phys. Rev. Lett. 103, 065001 (2009)]. Although the dependence of the radial velocity on the connection length of the magnetic field appeared to be different, a plausible explanation based on enhanced short-circuiting of the current path can be proposed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3640494].
146. Xiaolong Liu, Kazuo Nakamura, Tatsuya Yoshisue, Osamu Mitarai, Makoto Hasegawa, Kazutoshi Tokunaga, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Kuniaki Araki, Study of Matrix Converter as Stabilizing Power Supply for Vertical Position Instability on QUEST Tokamak, Proc. 2011 Annual Conference of I.E.E. of Japan,Industry Applications Society,Okinawa,Sept. 6-8,2011, (※), 2011.09.
147. Kobayashi, T.; Inagaki, S.; Itoh, S-I; Ida, K.; Oldenbuerger, S.; Tsuchiya, H.; Nagayama, Y.; Kawahata, K.; Yamada, H.; Sasaki, M.; Fujisawa, A.; Itoh, K., Verification of wavelet analysis for a heat pulse propagation experiment, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/53/9/095012, 53.0, 9.0, 0.0-0.0, 095012, 2011.09, A new wavelet analysis method is used to study heat pulse propagation in magnetic confinement plasmas. The wavelet transform is applied to estimate the time evolution of the phase delay in heat pulse propagation with a fine temporal resolution. The procedure of analysis is explained in detail. The method is examined by taking an exemplary heat pulse propagation in the Large Helical Device. Various wavelet parameters are tested and the parameter region where relevant results are obtained is identified. Temporal resolution of the phase variation is evaluated from a convergence study..
148. Inagaki, S.; Tokuzawa, T.; Itoh, K.; Ida, K.; Itoh, S. -I.; Tamura, N.; Sakakibara, S.; Kasuya, N.; Fujisawa, A.; Kubo, S.; Shimozuma, T.; Ido, T.; Nishimura, S.; Arakawa, H.; Kobayashi, T.; Tanaka, K.; Nagayama, Y.; Kawahata, K.; Sudo, S.; Yamada, H.; Komori, A., Observation of Long-Distance Radial Correlation in Toroidal Plasma Turbulence, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.107.115001, 107.0, 11.0, 0.0-0.0, Article No. 115001, 2011.09, This Letter presents the discovery of macroscale electron temperature fluctuations with a long radial correlation length comparable to the plasma minor radius in a toroidal plasma. Their spatiotemporal structure is characterized by a low frequency of similar to 1-3 kHz, ballistic radial propagation, a poloidal or toroidal mode number of m/n = 1/1 (or 2/1), and an amplitude of similar to 2% at maximum. Nonlinear coupling between the long-range fluctuations and the microscopic fluctuations is identified. A change of the amplitude of the long-range fluctuation is transmitted across the plasma radius at the velocity which is of the order of the drift velocity..
149. Katsuyuki KAWASHIMA, Yasuhiro MIYOSHI, Stella OLDENBÜRGER, Shigeru INAGAKI, Hiroyuki ARAKAWA, Yoshihiko NAGASHIMA, Takuma YAMADA, Makoto SASAKI, Tatsuya KOBAYASHI, Kazuya URIU, Satoru SUGITA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae -I. ITOH and Kimitaka ITOH, Evaluation of Electron Temperature Fluctuations Using Two Different Probe Techniques in Plasma Assembly for Nonlinear Turbulence Analysis (PANTA), Plasma and Fusion Research, 6.0, RA, 4.0, Article No. 2406118, 2011.08, Electron temperature fluctuations are measured with a rotatable triple probe in PANTA. Effects of fluctuation phase are cancelled by aligning the probe pins in the propagation direction of fluctuations. Evaluated electron temperature fluctuations normalized by average electron temperature are much smaller than normalized density fluctuations and normalized floating potential fluctuations in low electron temperature PANTA plasma. Additionally conditional sampling technique is applied to a single probe measurement..
150. Liu, H. Q.; Hanada, K.; Nishino, N.; Ogata, R.; Ishiguro, M.; Zushi, H.; Nakamura, K.; Sakamoto, M.; Idei, H.; Fujisawa, A.; Hasegawa, M.; Higashizono, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Study of blob-like structures in QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2010.12.225, 415.0, 1.0, S620-S623, 2011.08, Blob-like structures are observed in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. The combined measurement with a fast camera and a movable Langmuir probe show that visible filamentary structures extended along field lines do correspond to over-dense plasma structures. Ion saturation current time trace shows a front-like asymmetric burst when a visible structure reaches the probe during its outward propagation. The typical radial velocity of the blob-like structure, V-b, was measured as similar to 1 km/s with the fast camera at the intermediate area. V-b increased as the blob-like structure moved along major radius, R (outward). The average velocity of E x B drift derived from the probe measurement, slightly larger than V-b, was also increased as the blob-like structure propagated to larger R. (C) 2010 Elsevier B.V. All rights reserved..
151. Nagashima, Yoshihiko; Itoh, Sanae-I.; Inagaki, Shigeru; Arakawa, Hiroyuki; Kasuya, Naohiro; Fujisawa, Akihide; Kamataki, Kunihiro; Yamada, Takuma; Shinohara, Shunjiro; Oldenbuerger, Stella; Yagi, Masatoshi; Takase, Yuichi; Diamond, Patrick H.; Itoh, Kimitaka, Non-Gaussian properties of global momentum and particle fluxes in a cylindrical laboratory plasma, PHYSICS OF PLASMAS, 10.1063/1.3601767, 18.0, 7.0, 0.0-0.0, 070701, 2011.07, Non-Gaussian statistical properties of the azimuthally averaged momentum and particle fluxes driven by turbulence have been simultaneously observed in inhomogeneous magnetized plasmas for the first time. We identified the stretched Gaussian distribution of the both fluxes and the transition from the point-wise distribution to averaged ones was confirmed. The change of the particle flux precedes that of the momentum flux, demonstrating that the momentum flux is induced by the relaxation of density gradient. (C) 2011 American Institute of Physics. [doi:10.1063/1.3601767].
152. Tatsuya KOBAYASHI, Shigeru INAGAKI, Hiroyuki ARAKAWA, Stella OLDENBÜRGER, Makoto SASAKI, Yoshihiko NAGASHIMA, Takuma YAMADA, Satoru SUGITA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Observation of Nonlinear Coupling between Low Frequency Coherent Modes and Background Turbulence in LMD-U, Plasma and Fusion Research, 6.0, RA, 4.0, Article No. 2401082, 2011.07, A solitary wave like fluctuating structure is observed in the Large Mirror Device-Upgrade (LMD-U) under relatively high neutral pressure conditions. Ion saturation current fluctuations are measured and Fourier and wavelet power spectra are calculated. Temporal behavior of fluctuation power and strength of nonlinear coupling of low frequency coherent mode and background turbulence in a specific frequency region is analyzed. This is achieved using wavelet spectral and bispectral analyses with conditional averaging..
153. K. Hanada, H. Zushi, H. Idei, K. Nakamura, M. Ishiguro, S. Tashima, E. I.Kalinnikova, M. Sakamoto, M. Hasegawa, A. Fujisawa, A. Higashijima, S. Kawasaki, H. Nakashima, H. Liu, O. Mitarai, T. Maekawa, A. Fukuyama, Y. Takase, J. Qian, Recent experiments and future collaborations on QUEST, JSPS-CAS Core University Program Seminar on Summary of 10-year Collaborations in Plasma and Nuclear Fusion Research Area 9?11 March 2011,Okinawa,Japan, 204.0, 204.0, 2011.07.
154. K. Nakamura, X. L. Liu, T. Yoshisue, O. Mitarai, K. Tokunaga, M. Hasegawa, H. Zushi, K. Hanada, A. Fujisawa, M. Sakamoto, H. Idei, S. Kawasaki, H. Nakashima, A. Higashijima, K. Araki , Venturini Method and Space Vector Modulation Method in Matrix Converter, Proc. International Conference on Electrical Engineering (ICEE2011),Hong Kong,July 11-14,2011, (※), 2011.07.
155. H. Idei, H. Zushi, K. Hanada, K. Nakamura, A. Fujisawa, M. Hasegawa, N. Yoshida, M. Sakamoto, H. Watanebe, K. Tokunaga, Y. Nagashima, A. Ejiri, M. Sakaguchi, E. Kalinnikova, M. Ishiguro, S. Tashima, A. Fukuyama, H. Igami, S. Kubo, S. K. Sharma, T. Ryokai, H. Q. Liu, M. Isobe, K. Nagaoka, H. Nakanishi, N. Nishino, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai, M. Kikuchi and K. Toi, Electron Cyclotron / Bernstein Wave Heating and Current Drive Experiments using Phased-array Antenna in QUEST, RADIO FREQUENCY POWER IN PLASMAS: Proceedings of the 19th Topical Conference, 1406.0, 1.0, 473.0-476.0, 2011.06, The phased‐array antenna system for Electron Cyclotron/Bernstein Wave Heating and Current Drive experiments has been developed in the QUEST. The antenna was designed to excite a pure O‐mode wave in the oblique injection for the O‐X‐B mode conversion experiments, and its good performances were confirmed at a low power level. The plasma current (<∼15 kA) with an aspect ratio of 1.5 was started up and sustained by only RF injection in the low‐density operations. The long pulse discharge of 10 kA was also attained for 37 s. The new density window to sustain the plasma current was observed in the high‐density plasmas. The single‐null divertor configuration with the high plasma current (<∼25 kA) was attained in the 17 s plasma sustainment..
156. Hanada, K.; Zushi, H.; Idei, H.; Nakamura, K.; Ishiguro, M.; Tashima, S.; Kalinnikova, E. I.; Sakamoto, M.; Hasegawa, M.; Fujisawa, A.; Higashijima, A.; Kawasaki, S.; Nakashima, H.; Liu, H.; Mitarai, O.; Maekawa, T.; Fukuyama, A.; Takase, Y.; Qian, J., Non-Inductive Start up of QUEST Plasma by RF Power, PLASMA SCIENCE & TECHNOLOGY, 10.1088/1009-0630/13/3/08, 13.0, 3.0, 307.0-311.0, 0.0, 2011.06, Both start-up and sustainment of plasma were successfully achieved by fully non-inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface reconstruction exhibited a plasma shape with an aspect ratio of below 1.5. The plasma current was dependent significantly on the launched microwave power and vertical magnetic field, while not affected by the mode of launched wave and the toroidal refractive index. Hard X-ray (HXR) emitted from energetic electrons accelerated by the microwave was observed, and the discharge with a plasma current over 4 kA followed the same trend as the number of photons of 10 keV to 12 keV. This suggests that the plasma current may be driven by energetic electrons. Based on the experimental conditions, alternative explanations of how the plasma current could be driven are discussed..
157. Xiaolong Liu, Kazuo Nakamura, Kazutoshi Tokunaga, Makoto Hasegawa, Kuniaki Araki, Yi Jiang, Tatsuya Yoshisue, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Simulation on Toroidal Field Power Supply of HL-2A Tokamak: Application of Dual DQ0 Transformation for Six-Phase Synchronous Generator Model, Engineering Sciences Reports,Kyushu University, Vol.33,pp.7-10, 2011.06.
158. Tatsuya KOBAYASHI, Yoshihiko NAGASHIMA, Shigeru INAGAKI, Hiroyuki ARAKAWA, Makoto SASAKI, Takuma YAMADA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Method for Estimating the Wavenumber of Standing Waves Using Three Langmuir Probes, Plasma and Fusion Research, 6.0, RA, 5.0, Article No. 1401050, 2011.05, A new method for estimating the wavenumber of a standing wave system by using three Langmuir probes is proposed. Analytical formulae are derived from a simple model in which two waves of the same frequency and the same wavenumber propagate in opposite directions. The proposed method can estimate the wavenumber correctly even if the two waves have equal amplitude..
159. Shigeru INAGAKI, Tokihiko TOKUZAWA, Kimitaka ITOH, Katsumi IDA, Sanae-I. ITOH, Naoki TAMURA, Satoru SAKAKIBARA, Naohiro KASUYA, Akihide FUJISAWA, Shin KUBO, Takashi SHIMOZUMA, Takeshi IDO, Seiya NISHIMURA, Hiroyuki ARAKAWA, Tatsuya KOBAYASHI, Masatoshi YAGI, Kenji TANAKA, Yoshio NAGAYAMA, Kazuo KAWAHATA, Shigeru SUDO, Hiroshi YAMADA, Akio KOMORI and LHD Experiment Group, Long Range Temperature Fluctuation in LHD, Plasma and Fusion Research, 6.0, RA, 9.0, Article No. 1402017, 2011.04, We report a detailed correlation technique to identify the long-range temperature fluctuation in the Large Helical Device. Correlation hunting has successfully realized the observation of electron temperature fluctuations, which are characterized by their correlation length comparable to the plasma minor radius, with low frequency of ∼ 1-3 kHz, ballistic radial propagation (at a speed of ∼1 km/s, of the order of diamagnetic drift velocity), spatial mode number of m/n = 1/1 (or 2/1), and amplitude of ∼2% at the maximum. Bicoherence analysis confirmed their nonlinear coupling with local microscopic turbulent fluctuations. This long-range temperature fluctuation is a possible carrier of fast propagation in transport processes observed so far. We also comment on the theoretical interpretation..
160. Nagashima, Yoshihiko; Inagaki, Shigeru; Kamakaki, Kunihiro; Arakawa, Hiroyuki; Yamada, Takuma; Shinohara, Shunjiro; Kawai, Yoshinobu; Yagi, Masatoshi; Fujisawa, Akihide; Itoh, Sanae-I; Itoh, Kimitaka; Takase, Yuichi, Development of radially movable multichannel Reynolds stress probe system for a cylindrical laboratory plasma, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.3557384, 82.0, 3.0, 1.0, Article No. 033503, 2011.03, A new radially movable multichannel azimuthal probe system has been developed for measuring azimuthal and radial profiles of electrostatic Reynolds stress (RS) per mass density of microscale fluctuations for a cylindrical laboratory plasma. The system is composed of 16 probe units arranged azimuthally. Each probe unit has six electrodes to simultaneously measure azimuthal and radial electric fields for obtaining RS. The advantage of the system is that each probe unit is radially movable to measure azimuthal RS profiles at arbitrary radial locations as well as two-dimensional structures of fluctuations. The first result from temporal observation of fluctuation azimuthal profile presents that a low-frequency fluctuation (1-2 kHz) synchronizes oscillating Reynolds stress. In addition, radial scanning of the probe system simultaneously demonstrates two-dimensional patterns of mode structure and nonlinear forces with frequency f = 1.5 kHz and azimuthal mode number m = 1. (C) 2011 American Institute of Physics. [doi:10.1063/1.3557384].
161. Akihide FUJISAWA, A Review-Observations of Turbulence and Structure in Magnetized Plasmas, Plasma and Fusion Research, 5.0, Rev, 24.0, Article No. 046, 2010.12, Magnetized plasma is an non-equilibrium matter rich in nonlinear phenomena; its structural formations are dominated by turbulence. This article provides a brief review of experiments and observations of phenomena occurring in turbulent plasmas, with an emphasis on the methodologies for characterizing turbulence, and visualizing the invisible structure created by turbulence and the internal couplings between the elemental waves that constitute turbulence. Zonal flows, streamers, blobs, and other phenomena are investigated by using analytical methods such as Fourier transformation, wavelet analysis, probabilistic density function analysis, bicoherence, wavelet bicoherence. Finally, the contemporary view of plasma turbulence is presented with discussion of unsolved transport issues in fusion plasmas, such as transport barrier formation and nonlocal transport..
162. Tatsuya KOBAYASHI, Shigeru INAGAKI, Hiroyuki ARAKAWA, Kunihiro KAMATAKI, Yoshihiko NAGASHIMA, Takuma YAMADA, Satoru SUGITA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae -I. ITOH and Kimitaka ITOH, Bispectral Analysis of Density and Potential Fluctuations in a High Neutral Density Cylindrical Plasma, Plasma and Fusion Research, 5.0, RA, 4.0, Article No. S2047, 2010.12, The structure of fluctuations in the Large Mirror Device-Upgrade (LMD-U) depends on the neutral density. In this study, we focus on the high neutral density plasma in which the potential and density fluctuation waveforms are nontrigonometric functions similar to sawtooth waves, and peaks in the power spectrum lie along a straight line when plotted as frequency versus wavenumber. Two-dimentional auto and cross bispectral analyses of Iis and/or Vf, which consider both the matching conditions for both the azimuthal wavenumber and the frequency, have been performed; significant couplings are observed at particular peak frequencies. Similarities and differences between the auto and cross bicoherence of Iis and/or Vf are discussed..
163. Kunihiro KAMATAKI, Sanae-I. ITOH, Shigeru INAGAKI, Hiroyuki ARAKAWA, Yoshihiko NAGASHIMA, Takuma YAMADA, Masatoshi YAGI, Akihide FUJISAWA and Kimitaka ITOH, ECRH Superposition on Linear Cylindrical Helicon Plasma in the LMD-U, Plasma and Fusion Research, 5.0, RA, 4.0, Article No. S2046, 2010.12, Electron cyclotron resonance heating (ECRH) is superimposed on a linear cylindrical helicon plasma in the Large Mirror Device-Upgrade (LMD-U) to study the fluctuation characteristics of high density helicon plasma with/without ECRH injection. The radial profiles of electron density and electron temperature rose by < 10 %, and the drift wave frequency decreased with the ECRH injection. Bicoherence analysis reveals that the nonlinear interaction between drift waves and broad frequency band components exists with or without ECRH injection..
164. Jiaqi DONG, Kaijun ZHAO, Longwen YAN, Wenyu HONG, Changxuan YU, Akihide FUJISAWA, Jun QIAN, Jun CHENG, Adi LIU, Tao LAN, Hailin ZHAO, Defeng KONG, Yi LIU, Yuan HUANG, Qiang LI, Xianming SONG, Qingwei YANG, Xuantong DING, Xuru DUAN and Yong LIU, Experimental Study of Turbulence and Zonal Flow in Edge Plasmas of the HL-2A Tokamak, Plasma and Fusion Research, 5.0, RA, 4.0, Article No. S2014, 2010.12, Measurements with a three dimensional set of Langmuir probe arrays have unambiguously demonstrated the coexistence of intensive low frequency zonal flows (LFZFs), geodesic acoustic modes (GAMs), low frequency fluctuations (LFFs) and high frequency ambient turbulence (HFAT) in the edge of HL-2A tokamak plasmas, by verifying the temporal and spatial characteristics of the electrostatic fluctuations. The intensity of the LFZFs is observed to increase and decrease with increases of ECRH power (∼ 300-700 kW) and safety factor q (∼ 3.5-6.2), respectively, and the intensity of the GAMs increases with the ECRH power as well as q. The radial wave number-frequency spectra of the LFZF show that the LFZF packets propagate outwards and inwards as equally likely events, while the GAM packets propagate predominantly outwards. The three wave coupling of the zonal flows, including the GAMs, and the LFFs with the HFAT is investigated in detail..
165. Takuma YAMADA, Sanae-I. ITOH, Shigeru INAGAKI, Yoshihiko NAGASHIMA, Shunjiro SHINOHARA, Naohiro KASUYA, Kenichiro TERASAKA, Kunihiro KAMATAKI, Hiroyuki ARAKAWA, Masatoshi YAGI, Akihide FUJISAWA and Kimitaka ITOH, Nonlinear Mode Couplings in a Cylindrical Magnetized Plasma, Plasma and Fusion Research, 5.0, RA, Article No. S2016, 2010.12, Nonlinear mode couplings in plasma turbulence generate mesoscale global structures, such as zonal flows and streamers. A streamer is a poloidally localized structure that is radially elongated. In the Large Mirror Device-Upgrade, a streamer structure was observed in the ion saturation-current fluctuation measured with a 64-channel poloidal Langmuir probe array. The bunching of waves was poloidally localized and rotated slowly in the ion diamagnetic direction. The frequency and poloidal mode number of its envelope corresponded to one particular mode, which was strongly coupled with many other modes. By calculating the radial biphase profile of three pronounced modes, including the particular mode, the streamer structure was confirmed to be radially elongated..
166. Hiroyuki ARAKAWA, Shigeru INAGAKI, Yoshihiko NAGASHIMA, Takuma YAMADA, Kunihiro KAMATAKI, Tatsuya KOBAYASHI, Satoru SUGITA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae -I. ITOH and Kimitaka ITOH, Probability Density Function of Density Fluctuations in Cylindrical Helicon Plasmas , Plasma and Fusion Research, 5.0, RA, Article No. S2044, 2010.12, The turbulence fluctuation spectra of linear magnetized plasmas are measured under various neutral pressure conditions. Strong turbulent waves and symmetric waves are observed in low and high neutral pressure conditions. In this study, we compare the radial structure of the probability density function (PDF) of these fluctuations. The characteristics of the PDFs are related to those of the radial and poloidal turbulent structures..
167. Zhao, K. J.; Dong, J. Q.; Yan, L. W.; Hong, W. Y.; Fujisawa, A.; Yu, C. X.; Li, Q.; Qian, J.; Cheng, J.; Lan, T.; Liu, A. D.; Zhao, H. L.; Kong, D. F.; Huang, Y.; Liu, Yi; Song, X. M.; Yang, Q. W.; Ding, X. T.; Duan, X. R.; Liu, Yong, Turbulence and zonal flows in edge plasmas of the HL-2A tokamak, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/52/12/124008, 52.0, 12.0, 0.0-0.0, 124008, 2010.12, Measurements with a toroidally and poloidally displaced three-dimensional set of Langmuir probe arrays have revealed details of turbulence, geodesic acoustic modes (GAMs), zonal flows and their interactions in the edge region of HL-2A tokamak plasmas. The coexistence of intensive low frequency zonal flows (LFZFs) off < 4 kHz and the GAMs of 7 kHz < f(GAM) < 20 kHz has been unambiguously demonstrated. The poloidal and toroidal symmetries of the flows, including the GAMs, are verified experimentally. In particular, the coherency of the flows over a large toroidal scale of 2100 mm at a magnetic flux surface is emphasized. The LFZF packets are shown to propagate outward and inward as equally likely events, whereas the predominantly outward propagation of the GAM packets is analyzed. The nonlinear three-wave coupling of the flows with ambient turbulence is shown with a bicoherency analysis and an envelope modulation of the latter by the former. The intensity of the LFZFs is observed to increase and decrease with increases in ECRH power (similar to 300-700 kW) and safety factor q similar to (3.5-6.2), respectively, whereas the intensity of the GAMs increases with increases in both ECRH power and q..
168. Yamada, T.; Itoh, S-I; Inagaki, S.; Nagashima, Y.; Kasuya, N.; Kamataki, K.; Arakawa, H.; Kobayashi, T.; Yagi, M.; Fujisawa, A.; Itoh, K., Observation of Quasi-Two-Dimensional Nonlinear Interactions in a Drift-Wave Streamer, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.105.225002, 105.0, 22.0, 0.0-0.0, Article No. 225002, 2010.11, A streamer, which is a bunching of drift-wave fluctuations, and its mediator, which generates the streamer by coupling with other fluctuations, have been observed in a cylindrical magnetized plasma. Their radial structures were investigated in detail by using the biphase analysis. Their quasi-two-dimensional structures were revealed to be equivalent with a pair of fast and slow modes predicted by a nonlinear Schrodinger equation based on the Hasegawa-Mima model..
169. H. Zushi, N. Nishino, K. Hanada H. Honma, H. Q. Liu, Y. Higashizono, M. Sakamoto, Y. Nakashima, M. Ishiguro, T. Ryoukai, S. Tashima, K. Nakamura, H. Idei, M. Hasegawa, A. Fujisawa, O. Mitarai, A. Fukuyama, Takeiri, Y. Takase, T. Maekawa, Y. Kishimoto, Study of Edge Turbulence from the Open to Closed Magnetic Field Configuration during the Current Ramp-up Phase in QUEST,, Proc. 23rd IAEA Fusion Energy Conference, 11-16 October 2010 Daejon, Korea, 2010.11.
170. Arakawa, H.; Inagaki, S.; Nagashima, Y.; Yamada, T.; Kamataki, K.; Kobayashi, T.; Sugita, S.; Yagi, M.; Kasuya, N.; Fujisawa, A.; Itoh, S-I; Itoh, K., Bifurcation of the plasma turbulence on LMD-U, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/52/10/105009, 52.0, 10.0, 12.0, Article No. 105009, 2010.10, Density fluctuation spectra are qualitatively modified depending on filling gas pressure and magnetic field strength in a linear magnetized plasma. Abrupt and spontaneous jumps between fluctuation states during a discharge are observed in the filling gas pressure-magnetic field plane. Those jumps are characterized using a spectrum pattern and have a bifurcation property on the plane..
171. Yoshihiko NAGASHIMA, Kenichi NAGAOKA, Kimitaka ITOH, Akihide FUJISAWA, Mitsutaka ISOBE, Tsuyoshi AKIYAMA, Chihiro SUZUKI, Shin NISHIMURA, Yasuo YOSHIMURA, Keisuke MATSUOKA, Shoichi OKAMURA, Yuichi TAKASE, Akira EJIRI, Sanae -I. ITOH, Masatoshi YAGI, and CHS Group, Observation of edge Reynolds stress increase preceding an L-H transition in Compact Helical System, Plasma and Fusion Research, 5.0, RC, Article No. 022, 2010.10.
172. H. Arakawa, S. Inagaki, Y. Nagashima, T. Yamada, K. Kamataki, T. Kobayashi, S. Sugita, M. Yagi, N. Kasuya, A. Fujisawa, K. Itoh and S.-I. Itoh, Probability Density Function of Density Fluctuations in Cylindrical Helicon Plasmas, Plasma and Fusion Research, 5.0, RA, Article No. S2044, 2010.10.
173. H. Zushi, N. Nishino, K. Hanada H. Honma, H. Q. Liu, Y. Higashizono, M. Sakamoto, Y. Nakashima, M. Ishiguro, T. Ryoukai, S. Tashima, K. Nakamura, H. Idei, M. Hasegawa, A. Fujisawa, O. Mitarai, A. Fukuyama, Takeiri, Y. Takase, T. Maekawa, Y. Kishimoto, Study of Edge Turbulence from the Open to Closed Magnetic Field Configuration during the Current Ramp-up Phase in QUEST, Proc.23rd IAEA Fusion Energy Conference, 10-16 October 2010,Daejon,Republic of Korea, 2010.10.
174. Fujisawa, A.; Shimizu, A.; Itoh, K.; Nagashima, Y.; Yamada, T.; Inagaki, S.; Matsuoka, K.; Itoh, S-I, Wavelet analyses using parallel computing for plasma turbulence studies, PHYSICS OF PLASMAS, 10.1063/1.3488244, 17.0, 10.0, 0.0-0.0, 104503, 2010.10, The wavelet analyses have been carried out, using a cluster of personal computer, on the signal of electric field fluctuations measured with heavy ion beam probes in the compact helical system stellarator. The results have revealed the intermittent characteristics of turbulence and of the nonlinear couplings between elemental waves of turbulence. The usage of parallel computing is found to successfully reduce the calculation time as inversely proportional to the CPU number used the cluster, which shows the nature of "embarrassingly parallel computation." The present example of the wavelet analyses clearly demonstrates the importance of the advanced analyzing methods and the parallel computation for the modern studies of plasma turbulence. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488244].
175. Yamada, Takuma; Itoh, Sanae-I.; Inagaki, Shigeru; Nagashima, Yoshihiko; Kamataki, Kunihiro; Arakawa, Hiroyuki; Yagi, Masatoshi; Fujisawa, Akihide; Itoh, Kimitaka, Study of Amplitude Correlation Technique in a Cylindrical Magnetized Plasma, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.79.085001, 79.0, 8.0, 0.0-0.0, 085001, 2010.08, 0.0.
176. Inagaki, S.; Tamura, N.; Ida, K.; Kubo, S.; Shimozuma, T.; Nagayama, Y.; Kawahata, K.; Sudo, S.; Fujisawa, A.; Itoh, K.; Itoh, S-I., Internal transport barrier formation induced by edge perturbation on LHD, NUCLEAR FUSION, 10.1088/0029-5515/50/6/064012, 50.0, 6.0, Article No. 064012, 2010.06, The electron internal transport barrier (ITB) is formed by an edge perturbation induced by a tracer encapsulated solid pellet injection in a net-current free LHD plasma. The ITB trigger by an edge perturbation takes place in the low density regime and the ITB is not accompanied by a significant change in the density. At the onset of the core temperature rise, there is a strong correlation between the heat flux in the central region and the temperature gradient at a distance half of the plasma radius away. A radial temperature profile with a concave curvature abruptly appears in the growing phase of temperature gradient. Turbulence suppression mechanisms via flow and magnetic shears are not sufficient to explain these features..
177. Yamada, T.; Itoh, S. -I.; Inagaki, S.; Nagashima, Y.; Shinohara, S.; Kasuya, N.; Terasaka, K.; Kamataki, K.; Arakawa, H.; Yagi, M.; Fujisawa, A.; Itoh, K., Two-dimensional bispectral analysis of drift wave turbulence in a cylindrical plasma, PHYSICS OF PLASMAS, 10.1063/1.3429674, 17.0, 5.0, 0.0-0.0, 052313, 2010.05, Bispectral analysis and multichannel measurement are becoming attractive investigation tools in plasma fluctuation studies. In the Large Mirror Device-Upgrade, the measurement of fluctuations in the ion saturation-current with a 64-channel poloidal Langmuir probe array was performed. The two-dimensional (2D) (poloidal wave number and frequency) power spectrum showed a number of pronounced peaks and broadband fluctuations in the poloidal wave number-frequency space. We applied 2D bispectral analysis, which considers both the matching conditions of poloidal wave number and frequency, to the spatiotemporal waveform, and confirmed the nonlinear couplings between coherent-coherent, coherent-broadband, and broadband-broadband fluctuation components. More than ten peaks were revealed to have as their origins only three original parent modes generated in the plasma. Comparison between the theoretical estimate and experimental observation for the bicoherence showed good agreement. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3429674].
178. H. Idei, M. Sakaguchi, E. I. Kalinnikova, K. Nagata, H. Zushi, K. Hanada, S. Tashima, M. Ishiguro, , H. Q. Liu, H. Igami3, S. Kubo, K. Nakamura, A. Fujisawa, M. Sakamoto, M. Hassegawa, Y. Higashizono, R. Ogata, T. Ryokai, S. K. Sharma, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai and Y. Kishimoto, Development of Phased-array Antenna System and Its Application to EBWH/CD Experiments in QUEST, 16th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating,Sanya,China, 269.0-274.0, (※), 2010.04.
179. Akihide FUJISAWA, Experimental Confinement Studies Beyond ITER, Plasma and Fusion Research, 5.0, RA, 7.0, Article No. S1005, 2010.03, The advantages of stellarators are discussed with an emphasis on the high density limit more than 10 times higher than that of tokamaks with the equivalent magnetic field strength. The comparison between stellerators and tokamaks in the light of the new paradigm of plasma turbulence and zonal flows is presented to propose a new optimization principle of magnetic field configuration. The roles of low-temperature devices should be recognized for further understanding of the plasma confinement even in the era of burning state plasmas.
180. G R Tynan, A Fujisawa and G McKee, A review of experimental drift turbulence studies, PLASMA PHYSICS AND CONTROLLED FUSION, 51.0, 11.0, 77.0, Article No. 113001, 2009.10, Experimental drift turbulence and zonal flow studies in magnetically confined plasma experiments are reviewed. The origins of drift waves, transition to drift turbulence and drift turbulence–zonal flow interactions in open field line and toroidal closed flux surface experiments are discussed and the free energy sources, dissipation mechanisms and nonlinear dynamics of drift turbulence in the core, edge and scrape-off layer plasma regions are examined. Evidence that turbulence across these regions is linked and that turbulence-driven zonal flows exist is presented, and evidence that these flows help regulate the turbulent scale lengths, amplitude and fluxes is summarized. Seemingly contradictory reports exist regarding the scale of turbulent transport events; gyro-Bohm behavior of turbulence correlation lengths as well as evidence for long-range transport phenomena both exist. Changes in turbulence during and after transport barrier formation are summarized and compared. The inferred turbulent particle and heat fluxes due to turbulent transport are usually consistent with global confinement, and edge plasma momentum transport appears to be linked to plasma flows at the last-closed flux surface and in the open field line region. However, inconsistencies between observed transport and turbulence have sometimes been reported and are pointed out here. Special attention is given to open issues, and suggestions for future experimental studies are given..
181. Nagashima Yoshihiko, A. Ejiri, Fujisawa Akihide, Y. Takase, Calculation of Beam Trajectories of a Heavy Ion Beam Probe Diagnostic in the TST-2 Spherical Tokamak, IEEJ Transactions on Fundamentals and Materials, 129.0, 9.0, 575.0-579.0, 2009.09.
182. K. Kamataki, S.-I. Itoh, Y. Nagashima, S. Inagaki, S. Shinohara, M. Yagi, T. Yamada, Y. Kawai, A. Fujisawa, K. Itoh, Dynamics of Drift and Flute Modes in Linear Cylindrical ECR Plasma, JOURNAL OF NUCLEAR MATERIALS, 8.0, 82.0-86.0, Series 8 (2009) 82, 2009.08.
183. T. Yamada, S.-I. Itoh, S. Inagaki, Y. Nagashima, S. Shinohara, T. Maruta, K. Terasaka, K. Kamataki, N. Kasuya, M. Yagi, Y. Kawai, A. Fujisawa, K. Itoh, Measurement of Nonlinear Mode Couplings in the Large Mirror Device-Upgrade, JOURNAL OF NUCLEAR MATERIALS, Series 8 (2009) 87, 2009.08.
184. Arakawa, H.; Kamataki, K.; Inagaki, S.; Maruta, T.; Nagashima, Y.; Yamada, T.; Shinohara, S.; Terasaka, K.; Sugita, S.; Yagi, M.; Kasuya, N.; Fujisawa, A.; Itoh, S-I; Itoh, K., Observations of abrupt changes in the fluctuation spectrum on LMD-U, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/51/8/085001, 51.0, 8.0, 0.0-0.0, 085001, 2009.08, A transition of the fluctuation spectrum of ion saturation current is observed in linear magnetized plasmas. A power spectrum with regular peaks and a broadband spectrum appear alternately during a discharge. The temporal order of changes in the modes is investigated at the transition. The low poloidal mode number components change before the higher modes begin to change. The delay times of change between modes are determined..
185. Yoshihiko NAGASHIMA, Sanae-I. ITOH, Kimitaka ITOH, Akihide FUJISAWA, Shigeru INAGAKI, Yoshinobu KAWAI, Shunjiro SHINOHARA, Masayuki FUKAO, Takuma YAMADA, Kenichiro TERASAKA, Takashi MARUTA, Kunihiro KAMATAK, Hiroyuki ARAKAWA, Masatoshi YAGI, Naohiro KASUYA, George R. TYNAN, Patrick H. DIAMOND, and Yuichi Takase, Reynolds Stress Measurements for Investigation of Nonlinear Processes of Turbulence in the Large Mirror Device and in the Large Mirror Device-Upgrade, JOURNAL OF NUCLEAR MATERIALS, 8.0, 50.0-54.0, 2009.08.
186. Nagashima, Y.; Itoh, K.; Fujisawa, A.; Shinohara, K.; Itoh, S-I; Ido, T.; Yagi, M.; Hoshino, K.; Ejiri, A.; Takase, Y.; Uehara, K.; Miura, Y., Boundary of the geodesic acoustic eigenmode in the vicinity of the magnetic separatrix, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/51/6/065019, 51.0, 6.0, 10.0, Article No. 065019, 2009.06, We present a detailed investigation of the geodesic acoustic eigenmode(GAEM) profile in the vicinity of the last closed flux surface (LCFS) in the JFT-2M tokamak. Envelope and spectral peak frequency of the GAEM vanish near the LCFS obtained by an equilibrium reconstitution code. Spatial changes in mean plasma gradients (the electron temperature, electron density and floating potential) are correlated with the boundary. This does not contradict that the GAEM can have a node at the LCFS. Discussions of an inverse problem and the application of this GAEM measurement to an experimental test of the LCFS location calculated by the equilibrium reconstitution code are presented..
187. Sanae-I. ITOH, Seiya NISHIMURA, Kimitaka ITOH, Akihide FUJISAWA, Yoshihiko NAGASHIMA and Shigeru INAGAKI, Geodesic Acoustic Mode Spectroscopy II, Plasma and Fusion Research, 4.0, RC, 2.0, Article No. 014, 2009.05, An extension of geodesic acoustic mode (GAM) spectroscopy [Plasma Phys. Control. Fusion 49, L7 (2007)] is proposed. The ratio between the lowest frequency of the co-existing ion acoustic mode (IAM) and the frequency of GAM enables us to identify the safety factor of toroidal plasmas. The lowest frequency can be detected by bispectrum analysis when both GAM and IAM are excited. The possibility of measuring the safety factor is discussed..
188. Nagashima, Yoshihiko; Itoh, Sanae-I.; Shinohara, Shunjiro; Fukao, Masayuki; Fujisawa, Akihide; Terasaka, Kenichiro; Kawai, Yoshinobu; Tynan, George R.; Diamond, Patrick H.; Yagi, Masatoshi; Inagaki, Shigeru; Yamada, Takuma; Itoh, Kimitaka, Observation of the parametric-modulational instability between the drift-wave fluctuation and azimuthally symmetric sheared radial electric field oscillation in a cylindrical laboratory plasma, PHYSICS OF PLASMAS, 10.1063/1.3078075, 16.0, 2.0, 0.0-0.0, 020706, 2009.02, Observation of the parametric-modulational interaction between the drift-wave fluctuation (7-8 kHz) and azimuthally symmetric sheared radial electric field structure (similar to 0.4 kHz) in a cylindrical laboratory plasma is presented. Oscillation of the sheared radial electric field is synchronized at modulations of the radial wave number and Reynolds stress per mass density of the drift-wave spectrum. Bispectral analysis at the location where the sheared radial electric field has finite radial wave numbers shows that nonlinear energy transfers from the drift wave to the sheared radial electric field occur. Nonlocal energy transfers of fluctuations via "channel of the azimuthally symmetric sheared radial electric field" in spectral space as well as real space are discovered..
189. Akihide Fujisawa, A review of zonal flow experiments, NUCLEAR FUSION, 49.0, 1.0, 42.0, Article No. 013001, 2009.01, The present status of zonal flow experiments is reviewed with the historical process to attain the concept of zonal flows, which provides a new framework for understanding turbulence and transport in toroidal plasmas. The existence of zonal flows is experimentally confirmed to present a new paradigm of plasma turbulence. The paper presents contemporary experiments on zonal flows as major topics with a brief presentation of the zonal flow theories, the diagnostics and data processing techniques for turbulence and zonal flows and the peripheral issues of zonal flow physics. The accumulated experimental results introduced in this review include identification of zonal flows (both stationary zonal flows and geodesic acoustic modes), nonlinear interactions between zonal flows and turbulence, quantification of turbulent Reynolds stress, flow dynamics, energy transfer dynamics between turbulent wave components and the effects of zonal flows on plasma transport. These results have given rise to a new paradigm, namely, that the plasma turbulence is a system of zonal flows and drift waves, with an emphasis on the interaction between the disparate scale structures, e.g. zonal flows (mesoscale) and turbulence (micro-scale)..
190. Nagashima, Yoshihiko; Itoh, Sanae-I; Shinohara, Shunjiro; Fukao, Masayuki; Fujisawa, Akihide; Terasaka, Kenichiro; Kawai, Yoshinobu; Kasuya, Naohiro; Tynan, George R.; Diamond, Patrick H.; Yagi, Masatoshi; Inagaki, Shigeru; Yamada, Takuma; Itoh, Kimitaka, Coexistence of Zonal Flows and Drift-Waves in a Cylindrical Magnetized Plasma, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.77.114501, 77.0, 11.0, Article No. 114501, 2008.11, Spatiotemporal structures of fluctuations with frequencies lower than the ion cyclotron frequency in a cylindrical magnetized plasma are investigated. Drift-wave and low-frequency zonal flow coexist. Electrostatic potentials of the zonal flow and the drift-wave are distributed widely in radius. The radial wave number profile of the zonal flow has a shear structure at the radial location where the drift-wave has a maximal normalized fluctuation amplitude. On the other hand, the radial wave number profile of the drift-wave shows vortex tilting, resulting in the generation of stationary turbulence Reynolds stress gradient per mass density. The envelope and bispectral analyses indicate significant nonlinear interactions between the zonal flow and the drift-wave..
191. Yoshihiko NAGASHIMA, Sanae -I. ITOH, Shunjiro SHINOHARA, Masayuki FUKAO, Akihide FUJISAWA, Kenichiro TERASAKA, Yoshinobu KAWAI, Naohiro KASUYA, Masatoshi YAGI, Shigeru INAGAKI, Takuma YAMADA and Kimitaka ITOH, Nonlinear energy transfer of drift-wave fluctuation in a cylindrical laboratory plasma, Plasma and Fusion Research, 3.0, RC, 2.0, Article No. 056, 2008.10, Nonlinear energy transfer of the drift-wave spectrum is investigated experimentally in a cylindrical laboratory plasma. Using the Hasegawa-Mima equation, the nonlinear transfer function of electrostatic potential energy in frequency space is estimated by bispectral analysis. The transfer function derived from the drift-wave spectrum indicates a forward cascading of energy transfer from fundamental to higher harmonic modes..
192. Yamada, Takuma; Itoh, Sanae-I.; Maruta, Takashi; Kasuya, Naohiro; Nagashima, Yoshihiko; Shinohara, Shunjiro; Terasaka, Kenichiro; Yagi, Masatoshi; Inagaki, Shigeru; Kawai, Yoshinobu; Fujisawa, Akihide; Itoh, Kimitaka, Anatomy of plasma turbulence, NATURE PHYSICS, 10.1038/nphys1029, 4.0, 9.0, 721.0-725.0, 2008.09, Turbulence is a state of fluids and plasma where nonlinear interactions including cascades to finer scales take place to generate chaotic structure and dynamics(1). However, turbulence could generate global structures(2), such as dynamo magnetic field, zonal flows(3), transport barriers, enhanced transport and quenching transport. Therefore, in turbulence, multiscale phenomena coevolve in space and time, and the character of plasma turbulence has been investigated in the laboratory(4-10) as a modern and historical scientific mystery. Here, we report anatomical features of the plasma turbulence in the wavenumber-frequency domain by using nonlinear spectral analysis including the bi-spectrum(11). First, the formation of the plasma turbulence can be regarded as a result of nonlinear interaction of a small number of irreducible parent modes that satisfy the linear dispersion relation. Second, the highlighted finding here, is the first identification of a streamer ( state of bunching of drift waves(12,13)) that should degrade the quality of plasmas for magnetic confinement fusion(14,15). The streamer is a poloidally localized, radially elongated global structure that lives longer than the characteristic turbulence correlation time, and our results reveal that the streamer is produced as the result of the nonlinear condensation, or nonlinear phase locking of the major triplet modes..
193. Kunihiro KAMATAKI, Sanae -I. ITOH, Yoshihiko NAGASHIMA, Shigeru INAGAKI, Shunjiro SHINOHARA, Masatoshi YAGI, Takuma YAMADA, Yoshinobu KAWAI, Akihide FUJISAWA and Kimitaka ITOH, Observation of Zonal Flow Type Oscillation in Linear Cylindrical ECR Plasmas, Plasma and Fusion Research, 3.0, L, 5.0, Article No. 047, 2008.08, Zonal flow type oscillation, which is driven by a small modulation of the electron cyclotron resonance (ECR) power in a low-frequency band (< 0.1 kHz), and its impact on drift wave turbulence are observed in linear cylindrical ECR plasmas by simultaneous spatiotemporal measurements with a multi-ring probe array. It is found that a potential low-frequency (< 0.1 kHz) oscillation can have a zonal flow type structure. Bicoherence analysis reveals that this zonal flow type oscillation has a nonlinear interaction with the drift mode. These results indicate that an electric field with zonal flow, which is excited externally, can modulate the drift mode amplitude, similar to spontaneous zonal flow..
194. Kunihiro KAMATAKI, Sanae -I. ITOH, Yoshihiko NAGASHIMA, Shigeru INAGAKI, Shunjiro SHINOHARA, Masatoshi YAGI, Takuma YAMADA, Yoshinobu KAWAI, Akihide FUJISAWA and Kimitaka ITOH, Observation of Zonal Flow Type Oscillation in Linear Cylindrical ECR Plasmas, Plasma and Fusion Research, 9.0, RA, Article No. 047, 2008.08.
195. Takuma YAMADA, Sanae -I. ITOH, Kenichiro TERASAKA, Naohiro KASUYA, Yoshihiko NAGASHIMA, Shunjiro SHINOHARA, Takashi MARUTA, Masatoshi YAGI, Shigeru INAGAKI, Yoshinobu KAWAI, Akihide FUJISAWA and Kimitaka ITOH, Spatiotemporal Behavior of Drift Waves in LMD-U, Plasma and Fusion Research, 3.0, RA, 4.0, Article No. S1021, 2008.08, In the LMD-U linear magnetized plasma, fluctuation measurements have been performed with multi-channel poloidal Langmuir probe arrays to investigate the spatiotemporal behaviors of drift wave turbulence. Two-dimensional (poloidal mode number-frequency) power spectrum showed not only fluctuation peaks but also the existence of a broadband fluctuation. The broadband fluctuation developed at high poloidal mode number and high frequency regions and not along the linear dispersion relation curve of drift wave modes. It showed shorter correlation time and poloidal length than the peaked fluctuations. Two-dimensional axial coherence was measured with two poloidal probe arrays separated in the axial direction. The axial coherence was strong for both the broadband fluctuation and peak fluctuations, suggesting the quasi-two-dimensional structure of the drift wave turbulence..
196. Shigeru INAGAKI, Naoki TAMURA, Yoshihiko NAGASHIMA, Tokihiko TOKUZAWA, Takuma YAMADA, Katsumi IDA, Takashi MARUTA, Shin KUBO, Kenichi TERASAKA, Takashi SHIMOZUMA, Yoshio NAGAYAMA, Kazuo KAWAHATA, Akio KOMORI, Shunjiro SHINOHARA, Akihide FUJISAWA, Masatoshi YAGI, Yoshinobu KAWAI, Sanae-I. ITOH, Kimitaka ITOH and the LHD experimental group, Transport Dynamics and Multi-Scale Coupling of Turbulence in LHD, Plasma and Fusion Research, 3.0, RA, 4.0, Article No. S1006, 2008.08, Spatiotemporal correlation of heat transport and micro- to meso- scale or macro-scale coupling of plasma turbulence are investigated in LHD plasmas, where fast propagation of a cold pulse and a non-local temperature rise are observed. Evidence of a timescale shorter than the diffusion time and a spatial scale longer than the micro-turbulence correlation length between core heat fluxes and edge temperature gradients is found. At the same time, an envelope of turbulent density fluctuations is also found to be modulated. Observation of low frequency (≤ 2 kHz) amplitude modulation of density fluctuation suggests the existence of meso- to macro-scale turbulent structures in the plasma, in which a non-local temperature rise takes place. Relationships between the turbulence with long radial correlation length and the edge-core coupling of heat transport are discussed..
197. Takuma YAMADA, Sanae -I. ITOH, Takashi MARUTA, Naohiro KASUYA, Shunjiro SHINOHARA, Yoshihiko NAGASHIMA, Masatoshi YAGI, Kenichiro TERASAKA, Shigeru INAGAKI, Yoshinobu KAWAI, Masayuki FUKAO, Akihide FUJISAWA and Kimitaka ITOH, Experimental Study of Drift Wave Turbulence in Linear Plasmas, Plasma and Fusion Research, 3.0, RA, 5.0, Article No. 044, 2008.07, Linear plasmas allow multi-point, low-temperature measurements with Langmuir probes. We measured ion saturation-current fluctuations of a Large Mirror Device-Upgrade linear plasma using a poloidal Langmuir probe array. By varying the discharge conditions, the spatiotemporal behavior showed a change from a coherent sine wave to a turbulent waveform through a periodic, modulated sine wave. The two-dimensional (poloidal wave number and frequency) power spectrum for each regime showed a single fluctuation peak, a peak and its harmonics, and a number of peaks in the poloidal wave number-frequency space. Bi-spectral analysis was performed for the turbulent regime, and showed the existence of nonlinear couplings among fluctuation peaks and broadband components..
198. Fujisawa, A.; Itoh, K.; Shimizu, A.; Nakano, H.; Ohshima, S.; Iguchi, H.; Matsuoka, K.; Okamura, S.; Minami, T.; Yoshimura, Y.; Nagaoka, K.; Ida, K.; Toi, K.; Takahashi, C.; Kojima, M.; Nishimura, S.; Isobe, M.; Suzuki, C.; Akiyama, T.; Ido, T.; Nagashima, Y.; Itoh, S. -I.; Diamond, P. H., Experimental studies of zonal flow and field in compact helical system plasma, PHYSICS OF PLASMAS, 10.1063/1.2889012, 15.0, 5.0, 0.0-0.0, Article No. 055906, 2008.05, The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa , in Plasma Physics and Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411] using twin heavy ion beam probes. The paper presents the experimental observations of stationary zonal flow, nonlinear couplings between zonal flow and turbulence, and the role of zonal flow in the improved confinement, together with the recent discovery of zonal magnetic field. The presented experimental results strongly support the new paradigm that the plasma transport should be considered as a system of drift wave and zonal flows, and provides the first direct evidence for turbulence dynamo that the structured magnetic field can be really generated by turbulence. (C) 2008 American Institute of Physics..
199. Tsuchiya, H.; Itoh, S-I; Fujisawa, A.; Kamataki, K.; Shinohara, S.; Yagi, M.; Kawai, Y.; Komori, A.; Itoh, K., Sheared flow generation and mode suppression in a magnetized linear cylindrical plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/50/5/055005, 50.0, 5.0, 0.0-0.0, 055005, 2008.05, In a magnetized cylindrical plasma produced with the electron cyclotron resonance (ECR) scheme, a sheared E x B-flow showing zonal flow (ZF) characteristics has been driven by ECR power modulation. This method was used to control the sheared flow, and allowed us to observe that a coherent mode (spontaneously driven in the plasma) becomes stabilized as the induced plasma flow amplitude increases. The stabilization of the mode is caused by the increase in the plasma flow shear; thus, the result demonstrates the fundamental process of the shearing effect of ZFs on turbulence, which is commonly observed in toroidal plasma confinement devices for fusion research..
200. Kamataki, K.; Itoh, S-I; Nagashima, Y.; Inagaki, S.; Shinohara, S.; Yagi, M.; Yamada, T.; Kawai, Y.; Fujisawa, A.; Itoh, K., Investigation of competitive oscillations between drift mode and flute mode in linear cylindrical ECR plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/50/3/035011, 50.0, 3.0, 0.0-0.0, Article No. 035011, 2008.03, A competitive coexistence between a drift mode and a flute mode has been investigated experimentally in a bounded cylindrical electron cyclotron resonance ( ECR) plasma. This competitive cycle was repeated during a whole continuous discharge. Competitive phenomena appeared in plasmas when the density scale length was close to the critical value: the drift mode is dominant and the flute mode is suppressed just below a critical value, but above this value, the flute mode grows abruptly and the drift mode is suppressed. In this phase, the density gradient increases temporally. A small crash takes place when the density scale length reaches a limit value, and then the density profile goes back to the previous states and thus the drift mode is excited and the flute mode is suppressed. The direct nonlinear coupling between the drift mode and the flute mode is weaker than the process of the second harmonic generation of each mode, suggesting that the growth and decay of them are closely related to the modification of the radial density profile..
201. Nagaoka, Kenichi; Isobe, Mitsutaka; Toi, Kazuo; Shimizu, Akihiro; Fujisawa, Akihide; Ohshima, Shunsuke; Nakano, Haruhisa; Osakabe, Masaki; Todo, Yasushi; Akiyama, Tsuyoshi; Nagashima, Yoshihiko; Suzuki, Chihiro; Nishimura, Shin; Yoshimura, Yasuo; Matsuoka, Keisuke; Okamura, Shoichi, Radial transport characteristics of fast ions due to energetic-particle modes inside the last closed-flux surface in the compact helical system, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.100.065005, 100.0, 6.0, 0.0-0.0, Article No. 065005, 2008.02, The internal behavior of fast ions interacting with magnetohydrodynamic bursts excited by energetic ions has been experimentally investigated in the compact helical system. The resonant convective oscillation of fast ions was identified inside the last closed-flux surface during an energetic-particle mode (EPM) burst. The phase difference between the fast-ion oscillation and the EPM, indicating the coupling strength between them, remains a certain value during the EPM burst and drives an anomalous transport of fast ions..
202. T. Minami, S. Okamura, T. Akiyama, K. Ida, T. Oishi, M. Isobe, H. Nakano, A. Fujisawa, K. Nagaoka, M. Yoshinura, C. Suzuki, Y. Yoshimura, K. Toi, S. Ohshima, M. Takeuchi, H. Iguchi, S. Nishimura, A. Shimizu, K. Matsuoka, C. Takahashi, Characteristics of high density edge transport barrier with reheat mode on CHS, JOURNAL OF NUCLEAR MATERIALS, 123 012006 (2008), 2008.01, Edge transport barrier (ETB) formation and a reheat mode have been simultaneously realized on the Compact Helical System (CHS). The new mode is induced by neutral particle reduction in the edge region, which is caused by shutting off fueling after a strong gas-puffing. When both the reheat mode and the ETB are simultaneously realized, the density reduction is suppressed by the ETB in the peripheral region, and the temperature continues to increase by the reheat mode. This mode provides an enhanced confinement in the high density region (bar ne ~ 1.2 × 1020mr-3) compared to the ETB formation without the reheat mode, because of a large suppression of an anomalous transport, which is confirmed with fluctuation measurements in the edge region..
203. K. Nagaoka, M. Isobe, K. Toi, K. Goto, T. Ito, Y. Todo, M. Osakabe, S. Ohshima, A. Shimizu, A. Fujisawa, H. Nakano, Y. Takeiri, K. Y. Watanabe, T. Akiyama, Y. Yoshimura, C. Suzuki, S. Nishimura, K. Matsuoka, S. Okamura, CHS group, Local observations of fast ion responses to energetic particle modes using a directional probe in the Compact Helical System (CHS), NUCLEAR FUSION, 48.0, 8.0, Article No. 084005, 2008.01.
204. Takuma YAMADA, -Sanae -I. ITOH, Takashi MARUTA, Shunjiro SHINOHARA, Naohiro KASUYA, Yoshihiko NAGASHIMA, Masatoshi YAGI, Kenichiro TERASAKA, Masato KAWAGUCHI, Shigeru INAGAKI, Yoshinobu KAWAI, Masayuki FUKAO, Akihide FUJISAWA and Kimitaka ITOH, Detection of Cascading in Drift Wave Turbulence Using Probe Array in Linear Plasmas, Plasma and Fusion Research, 2.0, RC, Article No. 051, 2007.12, Measurement of drift wave turbulence using multi-probe systems was performed in the Large Mirror Device-Upgrade linear plasma. We compared a drift wave's two-dimensional (poloidal wave number and frequency) power spectrum with its calculated linear dispersion relation. As a result, a few wave modes that satisfy the linear dispersion relation were observed. Moreover, cascades to non-mode peaks and broadband components that do not satisfy the dispersion relation were identified..
205. Yamada, T.; Nagashima, Y.; Inagaki, S.; Kawai, Y.; Yagi, M.; Itoh, S. -I.; Maruta, T.; Shinohara, S.; Terasaka, K.; Kawaguchi, M.; Fukao, M.; Fujisawa, A.; Itoh, K., Fine positioning of a poloidal probe array, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.2818796, 78.0, 12.0, Article No. 123501, 2007.12, Multipoint detection is an essential requirement for investigating plasma turbulence which is a highly nonlinear phenomenon in space and time. We have fabricated an array of 64-channel poloidal probes surrounding the linear cylindrical plasma named LMD-U in order to study turbulence properties, particularly the nonlinear mode couplings, in the domain of poloidal wave number and frequency. However, misalignments of probe tips produce spurious modes, which do not exist in the real plasma, to distort the precise wave number measurements. The paper presents the description of the 64-channel poloidal probe array with means to adjust the probe positions, with discussion on the effects of the misalignments on the wave number measurements. (C) 2007 American Institute of Physics..
206. Kenichiro TERASAKA, Shunjiro SHINOHARA , Yoshihiko NAGASHIMA, Takuma YAMADA, Masato KAWAGUCHI, Takashi MARUTA, Shigeru INAGAKI, Yoshinobu KAWAI, Naohiro KASUYA, Masatoshi YAGI, Akihide FUJISAWA, Kimitaka ITOH and Sanae-I. ITOH, A Study on Low-Frequency Fluctuations Using New Azimuthal Probe Array in High-Density Helicon Linear Plasma, Plasma and Fusion Research, 2.0, RC, 2.0, Article No. 031, 2007.11, In a high-density plasma produced by helicon waves in a linear device, a change from the coherent to broad-band density fluctuations was observed on increasing the magnetic field. The coherent mode exhibited the drift wave features, and a steady oscillation state was observed. When the magnetic field was increased, the fluctuation level increased, and the higher azimuthal Fourier components were excited. When the spectrum became broad at the higher magnetic field, the behavior of the azimuthal structure became complex and changed rapidly with time. The analysis performed using the movable probe array (48ch.-probe) decomposed the short-lived structure into poloidal mode-frequency space and indicated mode-mode coupling in the broad-band spectrum..
207. Chihiro SUZUKI, Tsuyoshi AKIYAMA, Akihide FUJISAWA, Katsumi IDA, Mitsutaka ISOBE, Keisuke MATSUOKA, Takashi MINAMI, Kenichi NAGAOKA, Shin NISHIMURA, Shoichi OKAMURA, Byron J. PETERSON, Akihiro SHIMIZU, Chihiro TAKAHASHI, Kazuo TOI and Yasuo YOSHIMURA, Determination of the Major Impurity Radiators in the Reheat Mode Discharges in the Compact Helical System, Plasma and Fusion Research, 2.0, RA, Article No. S1062, 2007.11, Radiation brightness and impurity behaviors have been studied for reheat mode discharges in the Compact Helical System (CHS) by three different types of impurity diagnostics. Total radiation power measured by a pyroelectric detector significantly reduces after entering the reheat mode, whereas the line-averaged radiation brightness measured by an absolute extreme ultraviolet (AXUV) photodiode array increases especially for a center viewing chord due to the impurity accumulation in the plasma core. One possible reason for this opposite behavior between the two bolometric detectors is the reduced sensitivity of the AXUV photodiode for lower energy photons in vacuum ultraviolet (VUV) region. This speculation is supported by temporal evolutions of VUV spectra measured by a grazing incidence spectrometer. These results demonstrate that the comparison of three impurity diagnostics would be beneficial to the determination of the major impurity radiators and a comprehensive understanding of impurity behaviors in the reheat mode discharges..
208. Ohshima, S.; Fujisawa, A.; Shimizu, A.; Nakano, H.; Iguchi, H.; Yoshimura, Y.; Nagaoka, K.; Minami, T.; Isobe, M.; Nishimura, S.; Suzuki, C.; Akiyama, T.; Takahashi, C.; Takeuchi, M.; Ito, T.; Watari, T.; Kumazawa, R.; Itoh, S-I; Itoh, K.; Matsuoka, K.; Okamura, S., Zonal flow driven by energetic particle during magneto-hydro-dynamic burst in a toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/11/013, 49.0, 11.0, 1945.0-1952.0, 0.0, 2007.11, The internal structural measurements of electric field and density using twin heavy ion beam probes have been performed to elucidate the nonlinear evolution of the magneto-hydro-dynamic (MHD) bursty phenomenon driven by the interaction with high-energy particles in a toroidal plasma. The results have given the finest observation of the internal structure of plasma quantities, such as electric field, density and magnetic field distortion, which nonlinearly develop during the MHD phenomenon. In particular, the finding of a new kind of oscillating zonal flow driven by interaction between energetic particles and MHD modes should be emphasized for burning state plasmas..
209. Fujisawa, A.; Ido, T.; Shimizu, A.; Okamura, S.; Matsuoka, K.; Iguchi, H.; Hamada, Y.; Nakano, H.; Ohshima, S.; Itoh, K.; Hoshino, K.; Shinohara, K.; Miura, Y.; Nagashima, Y.; Itoh, S.-I.; Shats, M.; Xia, H.; Dong, J. Q.; Yan, L. W.; Zhao, K. J.; Conway, G. D.; Stroth, U.; Melnikov, A. V.; Eliseev, L. G.; Lysenko, S. E.; Perfilov, S. V.; Hidalgo, C.; Tynan, G. R.; Holland, C.; Diamond, P. H.; Mckee, G. R.; Fonck, R. J.; Gupta, D. K.; Schoch, P. M., Experimental progress on zonal flow physics in toroidal plasmas, NUCLEAR FUSION, 10.1088/0029-5515/47/10/S19, 47.0, 10.0, S718-S726, 2007.10, The present status of experiments on zonal flows in magnetic confinement experiments is examined. The innovative use of traditional and modem diagnostics has revealed unambiguously the existence of zonal flows, their spatio-temporal characteristics, their relationship to turbulence and their effects on confinement. In particular, a number of observations have been accumulated on the oscillatory branch of zonal flows, named geodesic acoustic modes, suggesting the necessity for theories to give their proper description. In addition to these basic properties of zonal flows, several new methods have elucidated the processes of zonal flow generation from turbulence. Further investigation of the relationship between zonal flows and confinement is strongly encouraged as cross-device activity including low temperature, toroidal and linear devices..
210. Nagashima, Y.; Itoh, K.; Itoh, S-I; Fujisawa, A.; Yagi, M.; Hoshino, K.; Shinohara, K.; Ejiri, A.; Takase, Y.; Ido, T.; Uehara, K.; Miura, Y., In search of zonal flows by using direct density fluctuation measurements, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/10/002, 49.0, 10.0, 1611.0-1625.0, 2007.10, A method for zonal flow study by using direct density fluctuation measurements is proposed. When ambient drift-wave turbulence is modulated by zonal flows (i.e. in the drift-wave-zonal flow systems), an envelope of the ambient density fluctuations has spectral peaks around zonal flow frequencies. A spectral peak at the geodesic acoustic mode (GAM) frequency is observed in the envelope of the ambient density fluctuations measured in edge plasma of the JFT-2M tokamak. The significant cross-bicoherence is also found between the ambient density fluctuations and its envelope in the GAM frequency. This result demonstrates that we can measure the GAM only by using density fluctuation data. This method provides a possibility of zonal flow research in burning core plasma by density fluctuation diagnostics such as microwave reflectometry..
211. Itoh, S-I; Itoh, K.; Sasaki, M.; Fujisawa, A.; Id, T.; Nagashima, Y., Geodesic acoustic mode spectroscopy, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/8/L01, 49.0, 8.0, 2007.08, A new kind of plasma diagnostics, geodesic acoustic mode (GAM) spectroscopy, is proposed. Radial eigenmodes of GAMs with discrete eigenfrequencies in toroidal plasmas are analysed. The eigenmode has a wavelength of the order of p(T)(2/3) L-T(1/3) (p(i) the ion gyroradius, L-T the temperature PT T I gradient scale length) and has the highest peak near the radius where the eigenfrequency coincides with the local GAM,frequency. Therefore, observing the radial position of the highest peak of the eigenmode provides a method to measure the local ion sound velocity. A novel method to measure the ion composition is given, combined with densities and temperatures..
212. S-I. Itoh, K. Itoh, M. Sasaki, A. Fujisawa, T. Ido, Y. Nagashima, Geodesic acoustic mode spectroscopy
, PLASMA PHYSICS AND CONTROLLED FUSION, 49.0, 8.0, L7, 49 L7 (2007), 2007.08.
213. Toda, S.; Itoh, K.; Fujisawa, A.; Itoh, S.-I.; Yagi, M.; Fukuyama, A.; Diamond, P. H.; Ida, K., Transport analysis of the effect of zonal flows on electron internal transport barriers in toroidal helical plasmas, NUCLEAR FUSION, 10.1088/0029-5515/47/8/024, 47.0, 8.0, 914.0-919.0, 0.0, 2007.08, The role of zonal flows in the formation of transport barrier in helical plasmas is analysed using the transport code. A set of one-dimensional transport equations is analysed, including the effect of zonal flows. The turbulent transport coefficient is shown to be suppressed when the plasma state takes the strong positive radial electric field. This bifurcation of the turbulent transport is newly caused by the change of the damping rate of zonal flows. It is theoretically demonstrated that the damping rate of zonal flows plays an important role in global confinement in toroidal plasmas..
214. Itoh, Kimitaka; Toda, Shinichiro; Fujisawa, Akibide; Itoh, Sanae-I.; Yagi, Masatoshi; Fukuyama, Atsushi, Turbulent transport of poloidal momentum in toroidal Plasmas, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.76.084502, 76.0, 8.0, 0.0-0.0, 084502, 2007.08, In this article, we discuss the turbulent transport of the momentum (component perpendicular to main magnetic field) in toroidal plasmas. The fluctuations in the quasi-linear response tend to induce the shear of mean poloidal flow, as in the case of driving the zonal flows. The case in which the shear of mean poloidal flow and the mesoscale zonal flows coexist is studied. Zonal flows, which have a more rapid growth rate than the shear of mean flow, reaches the nonlinear saturation state, and modify the interaction between microscopic fluctuations and the shear of mean flow. Taking into account the screening effect of zonal flows, the shear of mean poloidal flow is subject to diffusive damping. Responses to the external force are also studied. A new bifurcation (from the state where mesoscale zonal flows are dominant to the one where zonal flows are suppressed) is found..
215. A. Fujisawa, A. Shimizu, H. Nakano, S. Ohshima, Evaluation of local magnetic field fluctuation in a toroidal plasma with heavy ion beam probe, PLASMA PHYSICS AND CONTROLLED FUSION, 49.0, 6.0, 845.0, 2007.06.
216. Fujisawa, A.; Itoh, K.; Shimizu, A.; Nakano, H.; Ohshima, S.; Iguchi, H.; Matsuoka, K.; Okamura, S.; Minami, T.; Yoshimura, Y.; Nagaoka, K.; Ida, K.; Toi, K.; Takahashi, C.; Kojima, M.; Nishimura, S.; Isobe, M.; Suzuki, C.; Akiyama, T.; Nagashima, Y.; Itoh, S.-I.; Diamond, P. H., Experimental evidence of a zonal magnetic field in a toroidal plasma, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.98.165001, 98.0, 16.0, Article No. 165001, 2007.04, A zonal magnetic field is found in a toroidal plasma. The magnetic field has a symmetric bandlike structure, which is uniform in the toroidal and poloidal directions and varies radially with a finite wavelength of mesoscale, which is analogous to zonal flows. A time-dependent bicoherence analysis reveals that the magnetic field should be generated by the background plasma turbulence. The discovery is classified as a new kind of phenomenon of structured magnetic field generation, giving insight into phenomena such as dipole field generation in rotational planets..
217. Fujisawa, Akihide; Shimizu, Akihiro; Nakano, Haruhisa; Ohshima, Shinsuke; Itoh, Kimitaka; Nagashima, Yoshihiko; Itoh, Sanae-I.; Iguchi, Harukazu; Yoshimura, Yasuo; Minami, Takashi; Nagaoka, Keiichi; Takahashi, Chihiro; Kojima, Mamoru; Nishimura, Shin; Isobe, Mitsutaka; Suzuki, Chihiro; Akiyama, Tsuyoshi; Ido, Takeshi; Matsuoka, Keisuke; Okamura, Shoichi; Diamond, Patrick H., Causal relationship between zonal flow and turbulence in a toroidal plasma, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.76.033501, 76.0, 3.0, 4.0, Article No. 033501, 2007.03, Electric field fluctuations are directly measured using twin heavy-ion-beam probes in Compact Helical System. The spectrum of the electric field fluctuation reveals the existence of a zonal flow at a frequency of less than 1 kHz, coherent modes with a long correlation length (conjectured as geodesic acoustic modes), and background turbulence. Analyses using a wavelet elucidate nonlinear interactions between these fluctuation components in disparate scales. The highlighted findings are that the turbulent fluctuations should be modulated in response to the direction of zonal flow, and should be suppressed, on average, by the zonal flow. This is the first observation that demonstrates the causal linkage between zonal flow and turbulence in toroidal plasmas at a high temperature..
218. Fujisawa, A.; Shimizu, A.; Nakano, H.; Ohshima, S.; Itoh, K.; Nagashima, Y.; Itoh, S. -I; Iguchi, H.; Yoshimura, Y.; Minami, T.; Nagaoka, K.; Takahashi, C.; Kojima, M.; Nishimura, S.; Isobe, M.; Suzuki, C.; Akiyama, T.; Ido, T.; Matsuoka, K.; Okamura, S.; Diamond, P. H., Intermittent characteristics in coupling between turbulence and zonal flows, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/3/002, 49.0, 3.0, 211.0-217.0, 2007.03, An extended application of Gabour's wavelet to bicoherence analysis succeeds in resolving the instantaneous structure of three wave couplings between disparate scale electric field fluctuations in the high temperature core in a toroidal plasma device named the compact helical system. The obtained results quantify an intermittent linkage between turbulence and zonal flows - a highlighted issue in the present plasma research. This is the first demonstration that the intermittent nature of the three wave coupling should underlie the turbulence power modulation due to zonal flows..
219. Itoh, K.; Toda, S.; Fujisawa, A.; Itoh, S. -I.; Yagi, M.; Fukuyama, A.; Diamond, P. H.; Ida, K., Physics of internal transport barrier of toroidal helical plasmas, PHYSICS OF PLASMAS, 10.1063/1.2435310, 14.0, 2.0, 0.0-0.0, 020702, 2007.02, The role of zonal flows (ZFs) in the formation of an internal transport barrier in a toroidal helical plasma is analyzed. The turbulent transport coefficient is shown to be suppressed when the plasma state changes from the branch of a weak negative radial electric field to the strong positive one. This new transition of turbulent transport is caused by the change of the damping rate of the ZFs. It is clearly demonstrated, theoretically and experimentally, that the damping rate of the ZFs governs the global confinement of toroidal plasmas.(c) 2007 American Institute of Physics..
220. A. Fujisawa, A. Shimizu, H. Nakano, S. Ohshima, H. Iguchi, Recipe for Fabricating Zeolite Ion Source for Plasma Probing, JAPANESE JOURNAL OF APPLIED PHYSICS, 46 1710 (2007), 2007.01.
221. H. Nakano, A. Fujisawa, A. Shimizu, S. Ohshima, H. Iguchi, Y. Yoshimura, and T. Minami, Reconstruction Method of Local Density Fluctuation for Heavy Ion Beam Probe Measurements, REVIEW OF SCIENTIFIC INSTRUMENTS, 78.0, Article No. 063502, 2007.01.
222. T Akiyama, S Okamura, T Minami, A Fujisawa, T Oishi, S Kado, M Takeuchi, K Toi, K Ida, M Yoshinuma, K Matsuoka, M Isobe, S Nishimura, C Suzuki, Y Yoshimura, K Nagaoka, C Takahashi and the CHS Experimental Group, Scaling of Power Threshold for Edge Transport Barrier Formation in CHS with Density, Magnetic Field and Magnetic Configuration, PLASMA PHYSICS AND CONTROLLED FUSION, 48.0, 11.0, 1683.0, 2006.11.
223. Takashi MINAMI, Shoichi OKAMURA , Tsuyoshi AKIYAMA, Mitsutaka ISOBE, Tetsutarou OISHI, Shinichiro KADO, Katsumi IDA , Akihide FUJISAWA, Haruhisa NAKANO, Kiichiro NAKAMURA, KenichiNAGAOKA, Mikiro YOSHINUMA, Chihiro SUZUKI, Yasuo YOSHIMURA, Masaki TAKEUCHI, Kazuo TOI, Shinsuke OHSHIMA, Harukazu IGUCHI, Shin NISHIMURA, Akihiro SHIMIZU, Keisuke MATSUOKA, Chihiro TAKAHASHI and CHS group, First Observation of High Density Edge Transport Barrier Formation during Reheat Mode of Helical Plasma in CHS, Plasma and Fusion Research, 1.0, RC, 2.0, Article No. 047, 2006.10, An improved confinement mode with reheat and edge transport barrier is observed in the Compact Helical System (CHS). This mode provides enhanced confinement in high density region (ne ˜ 1.2 × 1020 m-3) due to the increase in temperature while high density is maintained in the peripheral region..
224. Yoshihiko NAGASHIMA, Katsumichi HOSHINO, Kenichi NAGAOKA, Kouji SHINOHARA, Akihide FUJISAWA, Kazuya UEHARA, Yoshinori KUSAMA, Katsumi IDA, Yasuo YOSHIMURA, Shoichi OKAMURA, Keisuke MATSUOKA, Akira EJIRI, Yuichi TAKASE, Kimitaka ITOH, Masatoshi YAGI, Sanae-I. ITOH, JFT-2M group and CHS group, Experimental study of nonlinear processes in edge turbulence of toroidal plasmas, Plasma and Fusion Research, 1.0, RA, 15.0, Article No. 041, 2006.09, This paper presents experimental studies of nonlinear processes between meso-scale structures and turbulent fluctuations, by use of bispectral analysis, in the edge region of toroidal plasmas. In ohmically heated plasmas of the JFT-2M tokamak, the drift wave-zonal flow system is investigated by observation of the potential fluctuations. The total bicoherence is composed of two components, i.e., the peak at the geodesic acoustic mode (GAM) frequency and broadband distribution. The biphase is also obtained, which indicates the phase angle of coherent interaction between GAM oscillations and broadband fluctuations. Bispectral functions (e.g., magnitude and phase) give an order-of-estimate agreement for the drift wave-zonal flow systems. Bicoherence analysis is also applied to the edge plasmas of the high-confinement mode (H-mode) of the Compact Helical System (CHS). In the case of CHS plasmas, nonlinear couplings in a system composed of coherent global magneto-hydrodynamic (MHD) oscillations and broadband fluctuations (up to hundreds kHz range) have been observed. Bispectral analysis enhances our understanding of the self-regulation systems of various toroidal plasmas in which strong turbulence and meso-scale structures coexist..
225. Kimitaka ITOH, Sanae-I. ITOH, Patrick H. DIAMOND, Akihide FUJISAWA, Masatoshi YAGI, Tetsuo WATARI, Yoshihiko NAGASHIMA and Atsushi FUKUYAMA, Geodesic Acoustic Eigenmodes, Plasma and Fusion Research, 1.0, RC, 2.0, Article No. 037, 2006.07, The eigenmode of a geodesic acoustic mode in the presence of a temperature gradient is discussed. Eigenmodes are obtained and the characteristic wavelength scales as ρi2/3LT1/3 (ρi: ion gyroradius, LT: temperature gradient scale length). The direction of propagation is discussed..
226. Takashi MINAMI, Shoichi OKAMURA, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, Tetsutaro OHISHI, Haruhisa NAKANO, Katsumi IDA, Akihide FUJISAWA, Kiichiro NAKAMURA, Kenichi NAGAOKA, Mikiro YOSHINUMA, Chihiro SUZUKI, Yasuo YOSHIMURA, Kazuo TOI, Masaki NISHIURA, Shinsuke OHSHIMA, Zenzo NARUHIRO, Harukazu IGUCHI, Shin NISHIMURA, Akihiro SHIMIZU, Keisuke MATSUOKA and Chihiro TAKAHASHI, Study of Edge Transport Barrier Formation on CHS Plasma, Plasma and Fusion Research, 1.0, RA, 9.0, Article No. 032, 2006.06, An edge transport barrier (ETB) similar to the tokamak H-mode has been observed for beam-heated plasma with two co-injected Neutral Beam Injectors (NBIs) in CHS. The Hα emission showed a clear spontaneous drop followed by an increase of line-averaged electron density at the L-H transition. Stored energy increased by ˜ 40% with H-factor improvement up to ˜ 30% compared to the international stellarator scaling (ISS04v03). A rapid density increase in the edge region to two-times level of the L-mode was observed to accompany a ˜ 15% increase in the density gradient. An ETB was formed when the plasma density exceeded the lower density limit by ˜ 1.5 × 1013 cm-3 and the total NBI power exceeds the threshold level (Pdeposit / ne ˜ 200 × 10-13 kW/cm-3 at BT = 0.95 T, Rax = 92.1 cm, where Pdeposit is the deposited NBI power, ne is electron density, BT is troidal magnetic field strength and Rax is location of magnetic axis). The power threshold increased with the magnetic field strength, as in tokamak scaling, and depends on the magnetic field configuration of the helical plasma..
227. Nagashima, Y; Itoh, K; Itoh, SI; Hoshino, K; Fujisawa, A; Ejiri, A; Takase, Y; Yagi, M; Shinohara, K; Uehara, K; Kusama, Y, Observation of coherent bicoherence and biphase in potential fluctuations around geodesic acoustic mode frequency on JFT-2M, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/5A/S38, 48.0, 0.0, #-#, 0.0, 2006.05, Two types of small-poloidal wavelength low frequency floating potential fluctuations (similar to 1 kHz, and 10-15 kHz) are observed in the edge region of ohmically heated plasmas in the JFT-2M tokamak. The higher frequency fluctuations are inferred as geodesic acoustic modes (GAMs). Significant bicoherences between both modes and the broad-band fluctuations are observed simultaneously; however, frequency ranges are different. A significant bicoherence range is from 70 to 125 kHz at the lower frequency modes (LFM) and is from 20 to 125 kHz at the GAM. Phase angles at the significant bicoherences are coherent around pi. These results indicate that both modes are nonlinearly coupled to the broad-band fluctuations. Two spectral peaks are observed around the GAM frequency and the difference in peak frequencies is around the LFM frequency, suggesting nonlinear couplings between the LFM and the GAM. However, the modulation of the GAM by the LFM is not conclusive. In this paper, the results of the letter (Nagashima et al 2005 Phys. Rev. Lett. 95 095002) are presented in detail..
228. Itoh, K; Itoh, SI; Diamond, PH; Hahm, TS; Fujisawa, A; Tynan, GR; Yagi, M; Nagashima, Y, Physics of zonal flows, PHYSICS OF PLASMAS, 10.1063/1.2178779, 13.0, 5.0, 0.0-0.0, 055502, 2006.05, Zonal flows, which means azimuthally symmetric band-like shear flows, are ubiquitous phenomena in nature and the laboratory. It is now widely recognized that zonal flows are a key constituent in virtually all cases and regimes of drift wave turbulence, indeed, so much so that this classic problem is now frequently referred to as "drift wave-zonal flow turbulence." In this review, new viewpoints and unifying concepts are presented, which facilitate understanding of zonal flow physics, via theory, computation and their confrontation with the results of laboratory experiment. Special emphasis is placed on identifying avenues for further progress. (c) 2006 American Institute of Physics..
229. Fujisawa, A; Shimizu, A; Nakano, H; Ohsima, S; Itoh, K; Iguchi, H; Matsuoka, S; Okamura, S; Itoh, SI; Diamond, PH, Properties of turbulence and stationary zonal flow on transport barrier in CHS, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/5A/S36, 48.0, A365, 0.0, 2006.05, Spectral changes in electric field fluctuation are measured using twin heavy ion beam probes in compact helical system (CHS) before and after an internal transport barrier is broken down. Wavelet analysis reveals intermittent behaviour of the fluctuations and a significant correlation between fluctuation powers of the low (2.5 < f < 10 kHz) and high (30 < f < 250 kHz) ranges. The high frequency (turbulence) fluctuation increases with a decrease in the low frequency fluctuation after the back-transition. The change in the power distribution between these two frequency ranges may contribute to the improved transport on the barrier..
230. Nagashima, Y; Itoh, K; Itoh, SI; Fujisawa, A; Hoshino, K; Takase, Y; Yagi, M; Ejiri, A; Ida, K; Shinohara, K; Uehara, K; Kusama, Y, Bispectral analysis applied to coherent floating potential fluctuations obtained in the edge plasmas on JFT-2M, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S01, 48.0, 4.0, S1-S15, 2006.04, This paper presents results of bispectral analysis applied to floating potential fluctuations in the edge region of ohmically heated plasmas in the JAERI Fusion Torus-2 Modified (JFT-2M) tokamak. Inside the outermost surface of plasmas, coherent mode fluctuations, (CMs) in floating potential were observed around the frequency of the geodesic acoustic mode. The squared bicoherence shows significant nonlinear couplings between the CMs and background fluctuations. The biphase at the frequency of the CMs is localized around pi, while that at frequencies of background fluctuations distributes in a wide range. The total bicoherence at the frequency of the CMs is proportional to the squared amplitude of the CMs. These observations are consistent with the theoretical prediction on the drift wave-zonal flow systems. Interpretation of the absolute value of the total bicoherence is also discussed..
231. Nagashima, Y; Itoh, SI; Yagi, M; Itoh, K; Fujisawa, A; Hoshino, K; Shinohara, K; Uehara, K; Kusama, Y; Ejiri, A; Takase, Y, Convergence study of bispectral analysis in experiments of high temperature plasmas, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.2194016, 77.0, 4.0, 6.0, Article No. 045110, 2006.04, A convergence study of bispectral analysis on toroidal plasma turbulence is presented with a theoretical estimate of bicoherence for the system of the drift wave and zonal flow. Examples are chosen from the analysis of floating potential fluctuation in the edge region of the JFT-2M tokamak. The convergence properties of the bispectral functions are clarified for an oscillatory branch of zonal flow (or geodesic acoustic mode) and drift waves. The total squared bicoherence or the biphase converges inversely proportional to the realization number or to the square root of the realization number, respectively. The numbers of realizations to qualitatively converge and obtain a quantitatively significant value of bicoherence are discussed for the drift wave fluctuations and for the zonal flow. (c) 2006 American Institute of Physics..
232. Ido, T; Miura, Y; Kamiya, K; Hamada, Y; Hoshino, K; Fujisawa, A; Itoh, K; Itoh, SI; Nishizawa, A; Ogawa, H; Kusama, Y, Geodesic-acoustic-mode in JFT-2M tokamak plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S04, 48.0, 4.0, S41, 0.0, 2006.04, The characteristics of geodesic-acoustic-mode (GAM) are investigated through direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe.The amplitude of the GAM changes in relation to the radial position; it is small near the separatrix, reaches a local maximum at 3 cm inside the separatrix and then decreases again to 5 cm inside the separatrix. The frequency is constant in the range, though the predicted GAM frequency varies according to the temperature gradient. The correlation length is about 6 cm and comparable to the structure of the amplitude of the GAM. The results indicate the GAM has a radial structure which reflects. the local condition at about 3 m inside the separatrix.The phase relation between the GAM oscillation indicates that the GAM is a radial propagating wave.The interaction between the GAM and the ambient density fluctuation is shown by the high coherence between the GAM oscillation and the temporal behaviour of the ambient density fluctuation. Moreover, the phase relation between the electric field fluctuation of the GAM (E,,GAM) and the amplitude of the density fluctuation indicates that the modulation of the ambient density fluctuation delays the (E) over tilde (r,GAM). The causality between the GAM and the modulation of the density fluctuation is revealed..
233. Fujisawa, A; Itoh, K; Shimizu, A; Nakano, H; Ohsima, S; Iguchi, H; Matsuoka, K; Okamura, S; Itoh, SI; Diamond, PH, Spectrograph of electric field fluctuation in toroidal helical plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S03, 48.0, 4.0, #-#, 0.0, 2006.04, This is a report on fluctuation measurements using twin heavy ion beam probes in CHS. The observation shows that dozens of coherent modes with intermittent nature co-exist in an electron cyclotron heated plasma. The modes are found to have a long-distance correlation in the toroidal direction. The radial structure of the modes is evaluated in potential fluctuation. The characteristics are consistent with those of the geodesic acoustic modes..
234. Fujisawa, A; Shimizu, A; Nakano, H; Ohsima, S; Itoh, K; Iguchi, H; Yoshimura, Y; Minami, T; Nagaoka, K; Takahashi, C; Kojima, M; Nishimura, S; Isobe, M; Suzuki, C; Akiyama, T; Nagashima, Y; Ida, K; Toi, K; Ido, T; Itoh, SI; Matsuoka, K; Okamura, S; Diamond, PH, Turbulence and transport characteristics of a barrier in a toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S15, 48.0, 4.0, #-#, 0.0, 2006.04, Turbulence and zonal flow at, a transport barrier are studied with twin heavy ion beam probes in a toroidal helical plasma. A wavelet analysis is used to extract turbulence properties, e.g. spectra of both density and potential fluctuations, the coherence and the phase between them and the dispersion relation. Particle transport estimated from the fundamental characteristics is found to clearly rise with their intermittent activities after the barrier is broken down. Time-dependent analysis reveals that the intermittency of turbulence is correlated with the evolution of the stationary zonal flow..
235. Ohshima, Shinsuke ; Fujisawa, Akihide ; Shimizu, Akihiro ; Nakano, Haruhisa, Development of Zeolite Ion Source for Beam Probe Measurements of High Temperature Plasma, REVIEW OF SCIENTIFIC INSTRUMENTS, 77.0, 3.0, 4.0, Article No. 03B704 , 2006.03.
236. Fujita, T; Fukuda, T; Sakamoto, Y; Ide, S; Suzuki, T; Takenaga, H; Ida, K; Idei, H; Shimozuma, T; Fujisawa, A; , 4. 1 Formation Conditions of Electron Internal Transport Barriers in JT-60 U Plasmas[1], JAEA-Review, 2005.0, 20.0, Vol. , No. 2005, Pages 20, 2006.01.
237. M. Yokoyama, H. Maassberg, C. D. Beidler, V. Tribaldos, K. Ida, F. Castej?n, T. Estrada, A. Fujisawa, T. Minami, T. Shimozuma, Y. Takeiri, J. Herranz, S. Murakami, H. Yamada, Common Features of Core Electron Root Confinement in Helical Device, FUSION SCIENCE AND TECHNOLOGY, 50.0, 3.0, 327.0-342.0, 2006.01.
238. S. Ohshima, A. Fujisawa, A. Shimizu, H. Nakano, Observation of Internal Coherent Mode Structure using Heavy Ion Beam Probe, REVIEW OF SCIENTIFIC INSTRUMENTS, 77.0, Article No. 10F517, 2006.01.
239. Takaaki Fujita, Yoshiteru Sakamoto, Shunsuke Ide, Takahiro Suzuki, Hidenobu Takenaga, T Fukuda, K Ida, T Shimozuma, A Fujisawa, S Ohdachi, K Toi, H Idei, Transport in core plasmas. Formation conditions of electron internal transport barriers in JT-60U plasmas, Review of JT-60U experimental results in 2003 and 2004, (※), 2006.01.
240. A. Fujisawa, A. Shimizu, H. Nakano et al., Turbulence and transport characteristics on a barrier in a toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 48 S205 (2006), 2006.01.
241. F. Castejon, A. Fujisawa, K. Ida, J. N. Talmadge, T. Estrada, D. Lopez-Bruna, C. Hidalgo, L. Krupnik and A. Melnikov, Influence of magnetic topology on transport and stability in stellarators, PLASMA PHYSICS AND CONTROLLED FUSION, 47.0, 12B, B53, 2005.12.
242. M. Yokoyama, H. Maassberg, K. Ida, T. Estrada, F. Castejon, T. Minami, A. Fujisawa, O. Yamagishi, M. G. Shats, A. Dinklage, V. Tribaldos, C. D. Beidler, T. Shimozuma, Y. Takeiri, J. Herranz, S. Murakami, H. Yamada, Internal Transport Barrier Physics in Helical Systems, 15th International Stellarator Workshop, Madrid,3-7 Octobar 200, RT-03, 2005.10.
243. Itoh, K; Nagashima, Y; Itoh, SI; Diamond, PH; Fujisawa, A; Yagi, M; Fukuyama, A, On the bicoherence analysis of plasma turbulence, PHYSICS OF PLASMAS, 10.1063/1.2062627, 12.0, 10.0, 0.0-0.0, 102301, 2005.10, The bicoherence of fluctuations in a system of drift waves and zonal flows is discussed. In strong drift-wave turbulence, where broadband fluctuations are excited, the bicoherence is examined. A Langevin equation formalism of turbulent interactions allows us to relate the bicoherence coefficient to the projection of nonlinear force onto the test mode. The dependence of the summed bicoherence on the amplitude of zonal flows is clarified. The importance of observing biphase is also stressed. The results provide a basis for measurement of nonlinear interaction in a system of drift waves and zonal flow..
244. Shimizu, A. Fujisawa, S. Ohshima, H. Nakano, Consideration of Magnetic Field Fluctuation Measurements in Torus Plasma with a Heavy Ion Beam Probe, REVIEW OF SCIENTIFIC INSTRUMENTS, 76.0, Article No. 043504, 2005.01.
245. S. Okamura, T. Minami, T. Akiyama, T. Oishi, A. Fujisawa, K. Ida, H. Iguchi, M. Isobe, S. Kado, K. Nagaoka, K. Nakamura, S. Nishimura, K. Matsuoka, H. Matsushita, H. Nakano, M. Nishimura, S. Ohshima, A. Shimizu, C. Suzuki, C. Takahashi, K. Toi, Y. Yoshimura, M. Yoshinuma, CHS Group, Edge and internal transport barrier formation in CHS, NUCLEAR FUSION, 45.0, 863.0, 2005.01.
246. H Sanuki, K Itoh, A Fujisawa and J Q Dong, Effects of Sheared Flow on Microinstabilities and Transport in Plasmas, PLASMA SCIENCE & TECHNOLOGY, 7.0, 1.0, Article No. 2610, 2005.01, Theoretical and experimental studies associated with electric field effects on the stability and transport are briefly surveyed. The effects of radial electric field on the suppression and/or enhancement of various microinstabilities such as drift waves, flute mode and temperature gradient modes are discussed. The suppression of flow shear on the electron temperature gradient mode in plasmas with slightly hollow density profiles is investigated by solving the gyrokinetic integral eigenvalue equation. Comparison between theoretical predictions and experimental observations based on the HIBP measurements with high temporal and spatial resolutions is made in bumpy tori and heliotron (CHS) devices..
247. T. Watari, H. Hamada, A. Fujisawa, K. Toi, K. Itoh, Extension of geodesic acoustic mode theory to helical systems, PHYSICS OF PLASMAS, 12.0, 6.0, 8.0, Article No. 062304 , 2005.01, The present paper extends the theory of geodesic acoustic mode (GAM) oscillation, which so far has been applied to tokamaks, to helical systems. By using drift kinetic equations for three-dimensional equilibriums, a generalized dispersion relation is obtained including Landau damping. The oscillation frequency is obtained in terms of the squared sum of Fourier components of the magnetic field intensity expressed by means of magnetic flux coordinates. An analytic form of the collisionless damping rate of GAM is obtained by solving the dispersion relation perturbatively. It is found that the GAM frequency is higher in helical systems than in tokamaks and that damping rate is enhanced in multi-helicity magnetic configurations. However, damping rates are predicted to be small if the temperature of electrons is higher than that of ions..
248. Fujisawa, A; Itoh, K; Iguchi, H; Matsuoka, K; Okamura, S; Shimizu, A; Minami, T; Yoshimura, Y; Nagaoka, K; Takahashi, C; Kojima, M; Nakano, H; Ohsima, S; Nishimura, S; Isobe, M; Suzuki, C; Akiyama, T; Ida, K; Toi, K; Itoh, SI; Diamond, PH, Identification of zonal flows in a toroidal plasma, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.93.165002, 93.0, 16.0, 0.0-0.0, Article No. 165002, 2004.10, This Letter presents experimental confirmation of the presence of zonal flows in magnetically confined toroidal plasma using an advanced diagnostic system-dual heavy ion beam probes. The simultaneous observation of an electric field at two distant toroidal locations (similar to1.5 m apart) in the high temperature (similar to1 keV) plasma provides a fluctuation spectrum of electric field (or flow), a spatiotemporal structure of the zonal flows (characteristic radial length of similar to1.5 cm and lifetime of similar to1.5 ms), their long-range correlation with toroidal symmetry (n=0), and the difference in the zonal flow amplitude with and without a transport barrier. These constitute essential elements of turbulence-zonal flow systems, and illustrate one of the fundamental processes of structure formation in nature..
249. Akihide Fujisawa, Internal Transport Barrier and Bifurcation Phenomena in Stellarators, Fusion Science and Technology, 46.0, 1.0, 91.0-100.0, 2004.06.
250. Ida, K; Fujita, T; Fukuda, T; Sakamoto, Y; Ide, S; Toi, K; Inagaki, S; Shimozuma, T; Kubo, S; Idei, H; Fujisawa, A; Ohdachi, S; Yoshinuma, M; Funaba, H; Narihara, K; Murakami, S; Wakasa, A; Yokoyama, M; Takeiri, Y; Watanabe, KY; Tanaka, K; Liang, Y; Ohyabu, N, Comparison of electron internal transport barriers in the large helical device and JT-60U plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/46/5A/004, 46.0, 5A, A45-A50, PII S0741-3335(04)70388-7, 2004.05, Plasmas with an electron internal transport barrier (ITB), which is characterized by peaked electron temperature profiles, are obtained in the JT-60U tokamak and in the large helical device (LHD) when the electron cyclotron heating (ECH) is focused on the magnetic axis. The maximum values of R/L-Te, where R is the major radius and LT. is the scale length of the electron temperature gradient, are similar for the LHD and JT-60U ITB plasmas. However, there is a clear jump of R/L-Te observed in LHD but not in JT-60U in the ECH power scan. This result is consistent with the fact that the trigger mechanism of the electron ITB is the fast transition of the radial electric field from a small negative E, to a large positive E, in LHD and a change of the magnetic shear from positive to negative is required for the formation of the electron ITB in JT-60U. There are also differences in the electron temperature profiles inside the ITB. The flattening of the electron temperature profile inside the strong ITB could be explained by the sharp increase of q values observed in JT-60U, while no flattening of the electron temperature profile is observed in LHD, where the central q values stay low..
251. Fujita, T; Fukuda, T; Sakamoto, Y; Ide, S; Suzuki, T; Takenaga, H; Ida, K; Idei, H; Shimozuma, T; Fujisawa, A; Ohdachi, S; Toi, K, Formation conditions for electron internal transport barriers in JT-60U plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/46/5A/003, 46.0, 10A, A35-A43, PII S0741-3335(04)70644-2, 2004.05, The formation of electron internal transport barriers (ITBs) was studied using electron cyclotron (EC) heating in JT-60U positive shear (PS) and reversed shear (RS) plasmas with scan of neutral beam (NB) power. With no or low values of NB power and with a small radial electric field (Er) gradient, a strong, box-type electron ITB was formed in RS plasmas while a peaked profile with no strong electron ITBs was observed in PS plasmas within the available EC power. When the NB power and the Er gradient were increased, the electron transport in strong electron ITBs with EC heating in RS plasmas was not affected, while electron thermal diffusivity was reduced in conjunction with the reduction of ion thermal diffusivity, and strong electron and ion ITBs were formed in PS plasmas..
252. Fujisawa, A; Iguchi, H; Minami, T; Yoshimura, Y; Sanuki, H; Itoh, K; Isobe, M; Nishimura, S; Suzuki, C; Tanaka, K; Osakabe, M; Nomura, I; Ida, K; Okamura, S; Toi, K; Kado, S; Akiyama, R; Shimizu, A; Takahashi, C; Kojima, M; Itoh, SI; Matsuoka, K; Hamada, Y; Fujiwara, M, Observation of bifurcation properties of radial electric fields using a heavy ion beam probe, NUCLEAR FUSION, 10.1088/0029-5515/41/5/310, 41.0, 5.0, 575.0-584.0, 0.0, 2001.05, The bifurcated nature of the potential profile of a toroidal helical plasma is investigated in CHS using a heavy ion beam probe. The measurements reveal that three main branches of potential profile exist in ECR heated plasmas with a low density of (n) over tilde (e) approximate to 0.5 x 10(19) m(-3). The branches with higher central potential exhibit a rather strong radial electric field shear that should result in fluctuation reduction and formation of a transport barrier. An analysis of the pulsating behaviour in the potential suggests the existence of a fine structure in the potential profiles between the main branches. Lissajous and histogram expressions are useful in extracting the bifurcation characteristics of the potential structure..
253. Duorah, S; Ejiri, A; Lee, S; Iguchi, H; Fujisawa, A; Kojima, M; Matsuoka, K; Ishiyama, E; Hanada, K; Shiraiwa, S; Toyama, H; Takase, Y, Multilayer mirror based soft x-ray spectrometer as a high temperature plasma diagnostic, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.1324745, 72.0, 1.0, 1183.0-1187.0, 0.0, 2001.01, A fully calibrated multilayer mirror (MLM) based soft x-ray spectrometer has been developed and installed on the Compact Helical System (CHS). This MLM based spectrometer is a new approach to devising a soft x-ray spectrometer with medium time and energy resolutions. The spectrometer mainly consists of a MLM as the dispersive element and a 20-channel (p-i-n) pin diode array for the detection of the soft x-rays. Both the MLM and the pin diodes have been calibrated at the KEK (High Energy Accelerator Research Organization) Photon Factory for an energy range of 300-1200 eV. The reflectivity of the mirror was found to increase from 3% (photon energy of 335 eV) to 25% (photon energy of 1050 eV). The pin diodes were found to have almost 100% efficiency for creating electron-hole pairs in the calibrated energy range. The spectrometer was installed on the CHS with the aim of fast electron temperature measurement and study of fast magneto-hydrodynamic (MHD) events occurring in plasmas. The experiments show that in the energy range of measurement, the electron "temperature" determined from the slope of the soft x-ray spectrum is much lower than that measured by the Thomson scattering diagnostic. Analysis showed that the soft x-ray spectrum is highly contaminated by impurity emission. Therefore it may be possible to measure electron temperature with this diagnostic if we choose another energy range where we can measure the continuous spectrum. The present time resolution of the system is of the order similar to0.1 ms, which made it possible to study the behavior of the plasma during fast MHD events. Modulations in the soft x-ray intensity were observed during MHD events in CHS plasmas. Analysis of these shows that these may be due to modulations in the temperature or the impurity concentration. (C) 2001 American Institute of Physics..
254. Fujisawa, A; Iguchi, H; Minami, T; Yoshimura, Y; Tanaka, K; Itoh, K; Sanuki, H; Lee, S; Kojima, M; Itoh, SI; Yokoyama, M; Kado, S; Okamura, S; Akiyama, R; Ida, K; Isobe, M; Nishimura, S; Osakabe, M; Nomura, I; Shimizu, A; Takahashi, C; Toi, K; Matsuoka, K; Hamada, Y; Fujiwara, M, Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma, PHYSICS OF PLASMAS, 10.1063/1.1290483, 7.0, 10.0, 4152.0-4183.0, PII [S1070-664X(00)04310-X], 2000.10, The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System (CHS) [K. Matsuoka , Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411]. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied. (C) 2000 American Institute of Physics. [S1070-664X(00)04310-X]..
255. K Toi, M Takechi, M Isobe, N Nakajima, M Osakabe, S Takagi, T Kondo, G Matsunaga, K Ohkuni, M Sasao, S Yamamoto, S Ohdachi, S Sakakibara, H Yamada, KY Watanabe, DS Darrow, A Fujisawa, M Goto, K Ida, H Idei, H Iguchi, S Lee, S Kado, S Kubo, O Kaneko, K Kawahata, K Matsuoka, T Minami, S Morita, O Motojima, K Narihara, S Nishimura, N Ohyabu, Y Oka, S Okamura, T Ozaki, K Sato, M Sato, A Shimizu, T Shimozuma, Y Takeiri, K Tanaka, T Tokuzawa, K Tsumori, I Yamada, Y Yoshimura, Energetic ion driven MHD instabilities observed in the heliotron/torsatron devices Compact Helical System and Large Helical Device, NUCLEAR FUSION, 40.0, 7.0, 1349.0, 2000.07.
256. N Ohyabu, A Fujisawa, N Ashikawa, M Emoto, H Funaba, M Goto, Y Hamada, H Iguchi, K Ida, K Itoh, M Isobe, H Idei, S Inagaki, N Inoue, K Ikeda, S Kado, S Kubo, R Kumazawa, K Khlopenkov, O Kaneko, K Kawahata, A Komori, T Kobuchi, S Lee, Y Liang, T Minami, J Miyazawa, S Masuzaki, K Matsuoka, T Morisaki, S Morita, S Murakami, T Mutoh, S Muto, K Narihara, Y Nagayama, Y Nakamura, H Nakanishi, K Nishimura, S Nishimura, N Noda, I Nomura, T Notake, S Okamura, S Ohdachi, K Ohkubo, Y Oka, M Osakabe, T Ozaki, BJ Peterson, RO Pavlichenko, A Sagara, S Sakakibara, R Sakamoto, M Sasao, K Sato, H Sanuki, K Saito, M Sato, T Seki, A Shimizu, T Shimozuma, M Shoji, H Suzuki, S Sudo, H Sasao, Y Takeiri, K Tanaka, K Toi, T Tokuzawa, K Tsumori, K Tsuzuki, M Takechi, N Tamura, Y Torii, I Yamada, H Yamada, S Yamaguchi, K Yamazaki, M Yokoyama, Y Yoshimura, S Yamamoto, KY Watanabe, T Watanabe, T Watari, O Motojima, M Fujiwara, Thermal transport barrier in heliotron-type devices (Large Helical Device and Compact Helical System), PHYSICS OF PLASMAS, 7.0, 5.0, 1802.0-1808.0, 2000.05.
257. Fujisawa, A; Iguchi, H; Minami, T; Yoshimura, Y; Tanaka, K; Itoh, K; Sanuki, H; Itoh, SI; Isobe, M; Nishimura, S; Okamura, S; Matsuoka, K; Fujiwara, M, Transport barrier formation and bifurcation patterns of potential profiles in the compact helical system heliotron/torsatron, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/42/5A/309, 42.0, 0.0, #-#, 0.0, 2000.05, In the compact helical system, several bifurcation patterns have been observed in potential profiles of electron-cyclotron-heated plasmas. In a bifurcation pattern with a strong shear of radial electric field, an internal transport barrier is confirmed to be established for electron thermal energy. Probabilistic treatment with realization of the pattern or internal transport barrier is discussed..
258. Sanuki, H; Itoh, K; Yokoyama, M; Fujisawa, A; Ida, K; Toda, S; Itoh, I; Yagi, M; Fukuyama, A, Possibility of electric field bifurcation and internal transport barrier formation in LHD plasma, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.69.445, 69.0, 2.0, 445.0-450.0, 0.0, 2000.02, Theoretical analysis of the electric field bifurcation is made for the LHD plasma. For given shapes of plasma profiles; a region of bifurcation is obtained in a space of the plasma parameters. In this region of plasma parameters, the electric field domain interface is predicted to appear in the plasma column. The reduction of turbulent transport is expected to occur in the vicinity of the interface; inducing internal transport barrier. Within the present simple model, the electric field bifurcation associated with the internal transport barrier is predicted to be realized for the parameter of T-e(0) similar or equal to 2 keV and n(0) similar or equal to 10(18)(m(-3)). The boundary of the region of multiple solution is characterized by a scaling T-e(0) similar to [n(0)](0.4)..
259. K Toi, M Takechi, S Takagi, G Matsunaga, M Isobe, T Kondo, M Sasao, DS Darrow, K Ohkuni, S Ohdachi, R Akiyama, A Fujisawa, M Gotoh, K Ida, H Idei, H Iguchi, S Kado, M Kojima, S Kubo, S Lee, K Matsuoka, T Minami, S Morita, N Nikai, S Nishimura, S Okamura, M Osakabe, A Shimizu, Y Shirai, C Takahashi, K Tanaka, T Watari, Y Yoshimura, Global MHD modes excited by energetic ions in heliotron/torsatron plasmas, NUCLEAR FUSION, 39.0, 11Y, 1929.0, 1999.11.
260. S Okamura, K Matsuoka, R Akiyama, DS Darrow, A Ejiri, A Fujisawa, M Fujiwara, M Goto, K Ida, H Idei, H Iguchi, N Inoue, M Isobe, K Itoh, S Kado, K Khlopenkov, T Kondo, S Kubo, A Lazaros, S Lee, G Matsunaga, T Minami, S Morita, S Murakami, N Nakajima, N Nikai, S Nishimura, I Nomura, S Ohdachi, K Ohkuni, M Osakabe, R Pavlichenko, BJ Peterson, R Sakamoto, H Sanuki, M Sasao, A Shimizu, Y Shirai, S Sudo, S Takagi, C Takahashi, S Takayama, M Takechi, K Tanaka, K Toi, T Watari, K Yamazaki, M Yokoyama, Y Yoshimura, Confinement physics study in a small low aspect ratio helical device: CHS, NUCLEAR FUSION, 39.0, 9Y, 1337.0, 1999.09.
261. Takechi, M; Takagi, S; Matsunaga, G; Ohkuni, K; Shimizu, M; Toi, K; Ohdachi, S; Akiyama, R; Fujisawa, A; Gotoh, M; , Energetic-Ion-Driven Toroidal Alfvacute en Eigenmodes Observed in a Heliotron/Torsatron Plasma, Physical review letters, 83.0, 2.0, 312.0, 1999.07.
262. K Ida, M Osakabe, K Tanaka, T Minami, S Nishimura, S Okamura, A Fujisawa, K Yamazaki, Y Yoshimura, S Kubo, R Akiyama, DS Darrow, H Idei, H Iguchi, M Isobe, S Kado, T Kondo, S Lee, K Matsuoka, S Morita, I Nomura, S Ohdachi, M Sasao, A Shimizu, S Takagi, C Takahashi, S Takayama, M Takechi, K Toi, K Tsumori, T Watari, Transition from L mode to high ion temperature mode in CHS heliotron/torsatron plasmas, NUCLEAR FUSION, 39.0, 11Y, 1649.0, Vol. 39, No. 11Y, Pages 1649, 1999.04.
263. Fujisawa, A; Iguchi, H; Idei, H; Kubo, S; Matsuoka, K; Okamura, S; Tanaka, K; Minami, T; Ohdachi, S; Morita, S; Zushi, H; Lee, S; Osakabe, M; Akiyama, R; Yoshimura, Y; Toit, K; Sanuki, H; Itoh, K; Shimizu, A; Takagi, S; Ejiri, A; Takahashi, C; Kojima, M; Hidekuma, S; Ida, K; Nishimura, S; Isobe, M; Inoue, N; Sakamoto, R; Itoh, SI; Hamada, Y; Fujiwara, M, Electric pulsation and profile quantization in CHS heliotron/torsatron, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/41/3A/049, 41.0, 3A, A561, 1999.03, Radial electric field is a key physical quantity in determining the structure of toroidal helical plasmas, owing to the nonlinear dependence of transport on the, radial electric field. It has been observed that the potential profiles show various interesting patterns in space and time in the compact helical system (CHS) plasmas. In particular, the phenomenon of electric pulsation, clearly demonstrates the nature of bifurcation of radial electric field in toroidal helical plasmas..
264. Fujisawa, A; Iguchi, H; Minami, T; Yoshimura, Y; Sanuki, H; Itoh, K; Lee, S; Tanaka, K; Yokoyama, M; Kojima, M; Itoh, SI; Okamura, S; Akiyama, R; Ida, K; Isobe, M; Morita, S; Nishimura, S; Osakabe, M; Shimizu, A; Takahashi, C; Toi, K; Hamada, Y; Matsuoka, K; Fujiwara, M, Electron thermal transport barrier and density fluctuation reduction in a toroidal helical plasma, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.82.2669, 82.0, 13.0, 2669.0-2672.0, 1999.03, A thermal transport barrier resulting in a high central electron temperature of similar to 2 keV is established in the core of electron-cyclotron-resonance heated plasmas of the Compact Helical System Heliotron/Torsatron. The formation of the barrier is correlated with the reduction in the density fluctuations and with a structural change of the radial electric field profile at the barrier location. The results suggest that the decrease in fluctuation should contribute to a reduction of anomalous transport and a drastic increase in electron temperature at the barrier. [S0031-9007(99)08825-0]..
265. FUJISAWA Akihide, IGUCHI Harukazu, IDEI Hiroshi, KUBO Shin, LEE Seishu, MATSUOKA Keisuke, OKAMURA Shoichi, TANAKA Kenji, MINAMI Takashi, MORITA Shigeru, OHDACHI Satoshi, OSAKABE Masaki, AKIYAMA Ryuichi, YOSHIMURA Yasuo, TOI Kazuo, SANUKI Heiji, ITOH Kimitaka, TAKAHASHI Chihiro, KOJIMA Mamoru, HIDEKUMA Shigeru, IDA Katsumi, NISHIMURA Shin, EIIRI Akira, HAMADA Yasushi, ITOH Sanae-L1, INOUE Noriyuki, SAKAMOTO Ryuichi and FUJMARA Masami, Electric field bifurcation and transition in CHS heliotron/torsatron, JOURNAL OF NUCLEAR MATERIALS, 1.0, 84.0-87.0, 1998.12, Transition in radial electric field has been observed in CHS plasmas during a combined heating phase of ECH+NBI, using a heavy ion beam probe. The transition occurs in a timescale of a few dozen or a hundred microseconds. Radial current to induce the transition is evaluated by high temporal resolution of the heavy ion beam probe. Neoclassical dependence of radial electric field on a plasma parameter will be discussed to clarify the nonlinearity to allow the transition..
266. Fujisawa, A; Iguchi, H; Idei, H; Kubo, S; Matsuoka, K; Okamura, S; Tanaka, K; Minami, T; Ohdachi, S; Morita, S; Zushi, H; Lee, S; Osakabe, M; Akiyama, R; Yoshimura, Y; Toi, K; Sanuki, H; Itoh, K; Shimizu, A; Takagi, S; Ejiri, A; Takahashi, C; Kojima, M; Hidekuma, S; Ida, K; Nishimura, S; Isobe, M; Inoue, N; Sakamoto, R; Itoh, SI; Hamada, Y; Fujiwara, M, Discovery of electric pulsation in a toroidal helical plasma, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.81.2256, 81.0, 11.0, 2256.0-2259.0, 1998.09, A pulsating behavior of the electrostatic potential has been discovered in a low-density, high-electron-temperature plasma of the CHS heliotron/torsatron. The potential profiles were observed to swing repeatedly between two distinctive states in a constant external magnetic field under a continuous supply of particles and energy. The change of the potential profile, which occurs on a much faster time scale (microseconds) than the diffusive time scale (milliseconds), is accompanied by changes in density and temperature. This discovery clearly demonstrates that even in a low beta regime a toroidal helical plasma can produce a self-sustaining dynamic steady state, like the sawtooth oscillation in tokamaks..
267. Fujisawa, A; Iguchi, H; Sanuki, H; Itoh, K; Itoh, SI; Okamura, S; Matsuoka, K; Hamada, Y, Electric field bifurcation and transition in the core plasma of CHS, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/40/5/011, 40.0, 5.0, 627.0-630.0, 1998.05, In the CHS heliotron/torsatron, dynamic phenomena associated with transitions in radial electric field were observed during combined ECH+NBI heated plasmas. The observations with high temporal resolution confirmed a nonlinear relationship between radial electric field and radial current as the cause of these phenomena associated with electric field bifurcation..
268. Fujisawa, A; Iguchi, H; Idei, H; Kubo, S; Matsuoka, K; Okamura, S; Tanaka, K; Minami, T; Ohdachi, S; Morita, S; , Plasma and Beam Physics-Discovery of Electric Pulsation in a Toroidal Helical Plasma, Physical Review Letters, Vol. 81, No. 11, Pages 2256-2259, 1998.01.
269. Fujisawa, A; Iguchi, H; Sanuki, H; Itoh, K; Lee, S; Hamada, Y; Kubo, S; Idei, H; Crowley, TP; Akiyama, R; Tanaka, K; Minami, T; Ida, K; Nishimura, S; Morita, S; Kojima, M; Hidekuma, S; Itoh, SI; Takahashi, C; Inoue, N; Suzuki, H; Okamura, S; Matsuoka, K, Dynamic behavior of potential in the plasma core of the CHS heliotron/torsatron, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.79.1054, 79.0, 6.0, 1054.0-1057.0, 0.0, 1997.08, During combined electron cyclotron and neutral beam heating, an abrupt drop and rise in potential by about one half of the central electron temperature (similar to 400 V) was observed in the core of the compact helical system heliotron/torsatron plasma. Drastic changes of radial electric field between positive and negative states occur over periods as short as 60 mu s, which is much shorter than the energy confinement time scale of about a few milliseconds. A nonlinear relation between the radial electric field and radial current is obtained. This is the first experimental observation of a microsecond time scale spontaneous transition based on an electric field bifurcation in toroidal helical plasmas..
270. A Fujisawa, H Iguchi, S Lee, TP Crowley, Y Hamada, S Kubo, H Idei, H Sanuki, K Itoh, T Minami, K Tanaka, S Nishimura, K Ida, S Hidekuma, M Kojima, C Takahashi, S Okamura, K Matsuoka, Direct observation of potential profiles with a 200 keV heavy ion beam probe on the Compact Helical System, PHYSICS OF PLASMAS, 4.0, 5.0, 1357.0-1361.0, 1997.05.
271. T. Watari, R. Kumazawa, K. Nishimura, T. Mutoh, T. Seki, S. Masuda, T. Shoji, F. Simbo, T. Ido, R. Akiyama, A. Ando, A. Ejiri, A. Fujisawa, H. Idei, K. Ida, H. Iguchi, M. Isobe, M. Iwase, S. Kubo, T. Minami, K. Matsuoka, T. Morisaki, S. Morita, S. Mutoh, S. Murakami, K. Narihara, S. Okamura, T. Ozaki, M. Sasao, C. Takahashi, T. Kawamoto, K. Tanaka, J. Xu, J. M. Noterdaeme, D. A. Rasmussen, J. F. Lyon, J. B. Wilgen, D. E. Greenwood, D. J. Hoffman, E. F. Jaeger and M. Murakami, RF heating experiments in CHS and RF development for LHD, The twelfth topical conference on radio frequency power in plasmas, 403.0, 1.0, 57.0-64.0, Vol. 403, No. 1, Pages 57-64, 1997.04.
272. Sakakita, H; Sato, KN; Nomura, I; Hamada, Y; Nishizawa, A; Kawasumi, Y; Ida, K; Xu, J; Narihara, K; Toi, K; Ejiri, A; Seki, T; Adachi, K; Iguchi, H; Fujisawa, A; Liang, R; Sakamoto, M; Kano, Y; Hirokura, S; Hidekuma, S; Kojima, M, Measurement of ablation cloud parameters and plasma potential with on/off-axis pellet injection in the JIPP T-IIU tokamak, FUSION ENGINEERING AND DESIGN, 10.1016/S0920-3796(96)00655-2, 34.0, 329.0-332.0, 0.0, 1997.03, A pellet injection system with controllability of the injection angle has been developed and installed in the JIPP T-IIU tokamak. A long helical ablation cloud ('tail') has been observed when an ice pellet is injected into the tokamak plasma using the controllable injection angle system. The 'tail' does not flow along the direction of the total magnetic field lines of the torus. In order to understand the details of the ice pellet ablation structure in the 'tail mode', the local parameters of electron density and temperature within the ablation cloud are obtained by a spectroscopic method. The electron density determined from Stark broadening of the Balmer beta line is in the range 1.0 x 10(16) - 1.0 x 10(17) cm(-3), while the temperature obtained from the line-to-continuum intensity ratios is in the range 1-4 eV. It has also been observed by a heavy ion beam probe (HIBP) measurement that the potential at the plasma centre becomes more negative and the potential profile becomes deeper negatively after pellet injection. (C) 1997 Elsevier Science S.A..
273. Fujisawa, A; Iguchi, H; Lee, S; Crowley, TP; Hamada, Y; Hidekuma, S; Kojima, M; Kubo, S; Idei, H; Nishimura, K; , Potential profile measurements on compact helical system (CHS) using a 200 keV heavy ion beam probe, FUSION ENGINEERING AND DESIGN, 34.0, 649.0-651.0, 1997.01.
274. FUJISAWA, A; KUBO, S; IGUCHI, H; IDEI, H; MINAMI, T; SANUKI, H; ITOH, K; OKAMURA, S; MATSUOKA, K; TANAKA, K; , PROBE IN THE COMPACT HELICAL SYSTEM, Fusion energy 1996: proceedings of the Sixteenth International Conference on Fusion Energy, Vol. 2, No. , Pages 41, 1997.01.
275. K. TOI, K. N. SATO, Y. HAMADA, S. OHDACHI, H. SAKAKITA, A. NISHIZAWA, A. EJIRI, K. NARIHARA, H. KURAMOTO, Y. KAWASUMI, S. KUBO, T. SEKI, K. KITACHI, J. XU, K. IDA, K. KAWAHATA, I. NOMURA, K. ADACHI, R. AKIYAMA, A. FUJISAWA, J. FUJITA, S. HIDEKUMA, N. HIRAKI, S. HIROKURA, H. IDEI, T. IDO, H. IGUCHI, M. ISOBE, K. IWASAKI, O. KANEKO, Y. KANO, M. KOJIMA, J. KOOG, R. KUMAZAWA, T. KURODA, J. LI, R. LIANG, T. MINAMI, S. MORITA, K. OHKUBO, Y. OKA, S. OKAJIMA, M. OSAKABE, Y. SAKAWA, M. SASAO, K. SATO, T. SHIMPO, T. SHOJI, H. SUGAI, T. WATARI, I. YAMADA, K. YAMAUTI, Studies of Perturbative Plasma Transport, Ice Pellet Ablation and Sawtooth Phenomena in the JIPP T-IIU Tokamak, 16th Conference Proceedings of Fusion Energy, 1.0, 559.0, IAEA-CN-64/A6-S, 1996.10.
276. A Fujisawa, S Kubo, H Iguchi, H IDEI, T MINAMI, H SANUKI, K ITOH, S OKAMURA, K MATSUOKA, K TANAKA, S LEE, M KOJIMA, TP CROWLEY, Y HAMADA, M IWASE, H NAGASAKI, H SUZUKI, N INOUE, R AKIYAMA, M OSAKABE, S MORITA, C TAKAHASHI, S MUTO, A EJIRI, K IDA, S NISHIMURA, K NARIHARA, I YAMADA, K TOI, S OHDACHI, T OZAKI, A KOMORI, K NISHIMURA, S HIDEKUMA, K OHKUBO, DA RASMUSSEN, JB WILGEN, M MURAKAMI, T WATARI, M FUJIWARA, Experimental study of plasma confinement and heating efficiency through potential profile measurements with a heavy ion beam probe in the compact helical system, Proc. 16th IAEA Fusion Energy Conference, Montreal, Canada 1996, 2.0, 41.0-54.0, IAEA-CN-64/C1-5, 1996.01.
277. K. TOI, T. MORISAKI, S. SAKAKIBARA, A. EJIRI, H. YAMADA, S. MORITA, K. TANAKA, N. NAKAJIMA, S. OKAMURA, H. IGUCHI, K. IDA, K. TSUMORI, S. OHDACHI, K. NISHIMURA, K. MATSUOKA, J. XU, I. YAMADA, T. MINAMI, K. NARIHARA, R. AKIYAMA, A. ANDO, H. ARIMOTO, A. FUJISAWA, M. FUJIWARA, H. IDEI, O. KANEKO, K. KAWAHATA, A. KOMORI, S. KUBO, R. KUMAZAWA, T. OZAKI, A. SAGARA, C. TAKAHASHI, Y. TAKITA, T. WATARI , Impact of rotational transform profile control on plasma confinement and stability in CHS, Plasma Physics and Controlled Nuclear Fusion Research 1994: Fifteenth Conference Proceedings, Seville, Spain, 26 September-1 October 1994, Vol. 2, 2.0, 331.0, IAEA-CN-60/A6/C-P3, 1994.09.