Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Naohiro Kasuya Last modified date:2019.06.21

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


Papers
1. M. Sasaki, Y. Cayenne, A. Escarguel, S. Inagaki, N. Kasuya, K. Itoh, T. Kobayashi, Formation of spiral structures of turbulence driven by a strong rotation in magnetically cylindrical plasmas, PHYSICS OF PLASMAS, 10.1063/1.5085372, 26, 4, 2019.04.
2. M. Sasaki, K. Itoh, T. Kobayashi, N. Kasuya, A. Fujisawa, and S.-I. Itoh, Propagation direction of geodesic acoustic modes driven by drift wave turbulence, NUCLEAR FUSION, 10.1088/1741-4326/aad251, 58, 11, 2018.11.
3. N. Kasuya, M. Nunami, K. Tanaka, and M. Yagi, Numerical diagnostics of fluctuation spectrum in 3D magnetic configurations, NUCLEAR FUSION, 10.1088/1741-4326/aad784, 58, 10, 2018.10.
4. N. Kasuya, and M. Sasaki, Simulation Research on Competitive Nature of Plasma Turbulence in Linear Devices, FRONT-RUNNERS' SYMPOSIUM ON PLASMA PHYSICS IN HONOR OF PROFESSORS KIMITAKA ITOH AND SANAE-I. ITOH, 10.1063/1.5048718, 1993, 2018.08.
5. Y. Kawachi, S. Inagaki, K. Tomita, K. Yamasaki, F. Kin, Y. Kosuga, M. Sasaki, Y. Nagashima, N. Kasuya, K. Hasamada, B. Zhang, A. Fujisawa, Determination of Spatiotemporal Structure of Fluctuations by Statistical Averaging Method, Plasma and Fusion Research, DOI=10.1585/pfr.13.3401105, 13, 3401105, 2018.07.
6. F. Kin, K. Itoh, A. Fujisawa, Y. Kosuga, M. Sasaki, T. Yamada, S. Inagaki, S.-I. Itoh, T. Kobayashi, Y. Nagashima, N. 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.
7. T. Ohno, N. Kasuya, M. Sasaki, and M. Yagi, Global Mode Analysis of Ion-Temperature-Gradient Instabilities Using the Gyro-Fluid Model in Linear Devices, Plasma and Fusion Research, DOI: 10.1585/pfr.13.1401081, 13, 1401081, 2018.05.
8. M. Sasaki, K. Itoh, T. Ido, A. Shimizu, T. Kobayashi, H. Arakawa, N. Kasuya, A. Fujisawa, and S.-I. Itoh, Evaluation of Measurement Signal of Heavy Ion Beam Probe of Energetic-Particle Driven Geodesic Acoustic Modes, Plasma and Fusion Research, DOI=10.1585/pfr.13.3403040, 13, 3403040, 2018.03.
9. Naohiro Kasuya, Makoto Sasaki, Satoshi Abe, Masatoshi Yagi, On the radial eigenmode structure of drift wave instability with inhomogeneous damping in cylindrical plasmas, Journal of the Physical Society of Japan, 10.7566/JPSJ.87.024501, 87, 2, 2018.01, Plasma flows can be driven by turbulent stresses from excited modes in magnetized plasmas. Our recent numerical simulation of resistive drift wave turbulence in a linear device has shown that the radial inhomogeneity of the neutral density affects azimuthal flow generation by changing the phase structure of the most unstable eigenmodes. Eigenmode analyses show that the mode structure has a complex Bessel-type function shape in the central region of the plasma, and the imaginary part arises from the radial inhomogeneity of the damping term caused by ion-neutral collisions. The amplitude of turbulent stress is proportional to the inhomogeneity under a marginally stable condition. Global structural formation is an important factor for determining the plasma turbulent state, and this result clearly shows that several kinds of radial background distributions, the plasma and neutral densities in this case, can influence the global structures..
10. Makoto Sasaki, T. Kobayashi, K. Itoh, Naohiro Kasuya, Yusuke Kosuga, Akihide Fujisawa, Sanae Itoh, Spatio-temporal dynamics of turbulence trapped in geodesic acoustic modes, Physics of Plasmas, 10.1063/1.5008541, 25, 1, 2018.01, The spatio-temporal dynamics of turbulence with the interaction of geodesic acoustic modes (GAMs) are investigated, focusing on the phase-space structure of turbulence, where the phase-space consists of real-space and wavenumber-space. Based on the wave-kinetic framework, the coupling equation between the GAM and the turbulence is numerically solved. The turbulence trapped by the GAM velocity field is obtained. Due to the trapping effect, the turbulence intensity increases where the second derivative of the GAM velocity (curvature of the GAM) is negative. While, in the positive-curvature region, the turbulence is suppressed. Since the trapped turbulence propagates with the GAMs, this relationship is sustained spatially and temporally. The dynamics of the turbulence in the wavenumber spectrum are converted in the evolution of the frequency spectrum, and the simulation result is compared with the experimental observation in JFT-2M tokamak, where the similar patterns are obtained. The turbulence trapping effect is a key to understand the spatial structure of the turbulence in the presence of sheared flows..
11. Takuma Yamada, Inagaki Shigeru, Makoto Sasaki, Yoshihiko Nagashima, Fumiyoshi Kin, Hiroyuki Arakawa, Tatsuya Kobayashi, Kotaro Yamasaki, Naohiro Kasuya, Yusuke Kosuga, Akihide Fujisawa, Kimitaka Itoh, Sanae Itoh, Three-dimensional structure of the streamer in linear plasmas, Journal of the Physical Society of Japan, 10.7566/JPSJ.87.034501, 87, 3, 2018.01, The three-dimensional structures of the streamer and its carrier waves and mediator were observed in a linear plasma device for the first time. Not only the cross-sectional structure but also the axial structure was observed. While carrier drift waves, which form the streamer structure by nonlinear interaction, had an axial mode number of 1, the streamer and mediator had an axial mode number of 0. The relationship of these axial mode numbers is well explained by the matching condition of the nonlinear interaction between the carrier waves and the mediator..
12. Naohiro Kasuya, S. Abe, Makoto Sasaki, Inagaki Shigeru, T. Kobayashi, M. Yagi, Turbulence simulation taking account of inhomogeneity of neutral density in linear devices, Physics of Plasmas, 10.1063/1.5009803, 25, 1, 2018.01, It is important to consider a combination of inhomogeneities, which drive and/or damp instabilities in magnetized plasmas. The inhomogeneity of neutral particle density is taken into account for analyzing turbulent states in linear devices by combining two kinds of simulations in this research. One is a simulation for 2D profiles of neutral particles and the other is that for resistive drift wave turbulence. Radial and axial profiles of neutral particles are calculated by the Monte Carlo method with a configuration of linear device PANTA. The ratio for ionization of neutral particles depends on the electron temperature, and the higher temperature in the operation range makes the neutral density smaller near the center of the plasma. Then, the radial profile of the ion-neutral collision frequency is set by introducing these neutral density profiles into resistive drift wave turbulence simulations. Smaller ion-neutral collision frequency makes the instabilities more unstable, and its inhomogeneity enhances mean electrostatic potential formation. The eigenmode structure is changed with the inhomogeneous ion-neutral collision frequency, and convective derivative nonlinearity generates the azimuthal flow near the center of the plasma. Two roles of the neutral particles on the turbulence, the direct change in linear instabilities and formation of background flows, become clear..
13. Makoto Sasaki, K. Itoh, K. Hallatschek, Naohiro Kasuya, M. Lesur, Yusuke Kosuga, Sanae Itoh, Enhancement and suppression of turbulence by energetic-particle-driven geodesic acoustic modes, Scientific Reports, 10.1038/s41598-017-17011-y, 7, 1, 2017.12, We propose a novel mechanism of enhancement of turbulence by energetic-particle-driven geodesic acoustic modes (EGAMs). The dynamics of drift-wave-type turbulence in the phase space is investigated by wave-kinetic equation. Spatially inhomogeneous turbulence in the presence of a transport barrier is considered. We discovered that trapping of turbulence clumps by the EGAMs is the key parameter that determines either suppress or enhance turbulence. In regions where turbulence is unstable, EGAM suppresses the turbulence. In contrast, in the stable region, EGAM traps clumps of turbulence and carries them across the transport barrier, so that the turbulence can be enhanced. The turbulence trapped by EGAMs can propagate independent of the gradients of density and temperature, which leads to non-Fickian transport. Hence, there appear a new global characteristic velocity, the phase velocity of GAMs, for turbulence dynamics, in addition to the local group velocity and that of the turbulence spreading. With these effect, EGAMs can deteriorate transport barriers and affect turbulence substantially. This manuscript provides a basis to consider whether a coherent wave breaks or strengthen transport barriers..
14. Makoto Sasaki, Naohiro Kasuya, K. Itoh, S. Toda, Takuma Yamada, Yusuke Kosuga, Yoshihiko Nagashima, T. Kobayashi, H. Arakawa, K. Yamasaki, Akihide Fujisawa, Inagaki Shigeru, Sanae Itoh, Topological bifurcation of helical flows in magnetized plasmas with density gradient and parallel flow shear, Physics of Plasmas, 10.1063/1.5000343, 24, 11, 2017.11, The topological bifurcation of the flow in non-equilibrium magnetized plasmas is demonstrated by a turbulence simulation. A system with two generic sources of turbulence, the gradients of density and parallel flow, is considered. Topological index of the flow is introduced, in order to indicate the chirality of flow pattern. We here report that the turbulence-driven flow forms the structure of co-axial helixes with opposite chirality. By changing the source of plasma particles, which modifies the density gradient, the transition between three turbulent states is obtained. In addition to the two turbulent states, which are dominated by the drift wave and the D'Angelo mode, respectively, the new state is found. In this third state, fluctuations are driven by both of the free energy sources simultaneously, and compete with the others. The result illustrates the generic feature of turbulence flow generation in non-equilibrium magnetized plasmas..
15. Makoto SASAKI, Naohiro KASUYA, Shinichiro TODA, Takuma YAMADA, Yusuke KOSUGA, Hiroyuki ARAKAWA, Tatsuya KOBAYASHI, Shigeru INAGAKI, Akihide FUJISAWA, Yoshihiko NAGASHIMA, Kimitaka ITOH and Sanae-I ITOH, Multiple-Instabilities in Magnetized Plasmas with Density Gradient and Velocity Shears, Plasma and Fusion Research, DOI: 10.1585/pfr.12.1401042, 12, 1401042, 2017.08.
16. K. Itoh, Sanae Itoh, K. Ida, Inagaki Shigeru, Y. Kamada, K. Kamiya, J. Q. Dong, C. Hidalgo, T. Evans, W. H. Ko, H. Park, T. Tokuzawa, S. Kubo, T. Kobayashi, Yusuke Kosuga, Makoto Sasaki, G. S. Yun, S. D. Song, Naohiro Kasuya, Yoshihiko Nagashima, C. Moon, M. Yoshinuma, R. Makino, T. Tsujimura, H. Tsuchiya, U. Stroth, Hysteresis and fast timescales in transport relations of toroidal plasmas, Nuclear Fusion, 10.1088/1741-4326/aa796a, 57, 10, 2017.07, This article assesses current understanding of hysteresis in transport relations, and its impact on the field. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both core and edge plasmas. The modulation ECH experiment is explained, in which the heating power cycles on-and-off periodically, revealing hysteresis and fast changes in the gradientflux relation. The key finding is that hystereses were observed simultaneously in both the the gradientflux and gradientfluctuation relations. Hysteresis with rapid timescale exists in the channels of energy, electron and impurity densities, and plausibly in momentum. Advanced methods of data analysis are explained. Transport hysteresis can be studied by observing the higher harmonics of temperature perturbation δTm in heating modulation experiments. The hysteresis introduces the term δTm, which depends on the harmonic number m in an algebraic manner (not exponential decay). Next, the causes of hysteresis and its fast timescale are discussed. The nonlocal-in-space coupling works here, but does not suffice. One mechanism for the heating heats turbulence is that the external source S in phase space for heating has its fluctuation in turbulent plasma. This coupling can induce the direct input of heating power into fluctuations. The height of the jump in transport hysteresis is smaller for heavier hydrogen isotopes, and could be one of the origins of isotope effects on confinement. Finally, the impacts of transport hysteresis on the control system are assessed. Control systems must be designed so as to protect the system from sudden plasma loss..
17. Yasuhiro Nariyuki, Makoto Sasaki, Naohiro Kasuya, Tohru Hada, Masatoshi Yagi, Phase coherence among the Fourier modes and non-Gaussian characteristics in the Alfven chaos system, Progress of Theoretical and Experimental Physics, 10.1093/ptep/ptx016, 2017, 3, 2017.03, Non-Gaussian characteristics in time series of the Alfven chaos system are discussed. The phase coherence index, a measure defined by using the surrogate data method and the structure function, is used to evaluate the phase coherence among the Fourier modes. Through Monte Carlo significance testing, it is found that the phase coherence decays monotonically with increasing dissipative parameter and time scale. By applying the Mori projection operator method assuming the Markov process, a model equation for the time correlation function is derived from the generalized Langevin equation. As opposed to the result of the phase coherence analysis, it is concluded that the difference between the direct numerical simulation and the model equation becomes pronounced as the dissipative parameters are increased. This suggests that, even when the phase coherence index is not significant, the underlying physical system may be a non-Gaussian process..
18. Tatsuya KOBAYASHI, Sigeru INAGAKI, Makoto SASAKI, Yusuke KOSUGA, Hiroyuki ARAKAWA, Fumiyoshi KIN, Takuma YAMADA, Yoshihiko NAGASHIMA, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I. ITOH and Kimitaka ITOH, Phenomenological Classification of Turbulence States in Linear Magnetized Plasma PANTA, Plasma and Fusion Research, DOI: 10.1585/pfr.12.1401019 , 12, 1401019, 2017.03.
19. Naohiro Kasuya, M. Yagi, Radially Distributed Instabilities and Nonlinear Process to Generate Pressure Variation in a Torus Plasma, Plasma and Fusion Research, 10.1585/pfr.12.1303005, 12, 2017.02.
20. M. Sasaki, Naohiro Kasuya, K. Itoh, Yusuke Kosuga, M. Lesur, K. Halatschek, Sanae-I. Itoh, Toroidal momentum channeling of geodesic acoustic modes driven by fast ions, Nuclear Fusion, 2017.01.
21. M. Sasaki, Naohiro Kasuya, K. Itoh, K. Hallatschek, M. Lesur, Sanae-I. Itoh, A branch of energetic-particle driven geodesic acoustic modes due to magnetic drift resonance, Physics of Plasmas, 2016.10.
22. T. Kobayashi, S. Inagaki, Yusuke Kosuga, M. Sasaki, Nagashima Yoshihiko, Takuma Yamada, H. Arakawa, Naohiro Kasuya, Fujisawa Akihide, Sanae-I. Itoh, K. Itoh, Structure formation in parallel ion flow and density profiles by cross-ferroic turbulent transport in linear magnetized plasma, Physics of Plasmas, 2016.10.
23. F. Kin, Takuma Yamada, S. Inagaki, Nagashima Yoshihiko, H. Arakawa, T. Kobayashi, Y. Miwa, Naohiro Kasuya, M. Sasaki, Yusuke Kosuga, Fujisawa Akihide, K. Itoh, Sanae-I. Itoh, Changes of Particle Flux during End-Plate Biasing Experiment in PANTA, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 10.7566/JPSJ.85.093501, 85, 9, 2016.09.
24. H. Arakawa, M. Sasaki, Yusuke Kosuga, T. Kobayashi, Naohiro Kasuya, Nagashima Yoshihiko, Takuma Yamada, M. Lesur, Fujisawa Akihide, K. Itoh, Sanae-I. Itoh, Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma, SCIENTIFIC REPORTS, 10.1038/srep33371, 6, 2016.09.
25. K. Itoh, Sanae-I. Itoh, T. Kobayashi, K. Kamiya, T. Ido, T. Tokuzawa, S. Inagaki, Naohiro Kasuya, On the origin of steep and localized radial electric field in the transport barrier at plasma edge, Contributions to Plasma Physics, 10.1002/ctpp.201610042, 56, 6-8, 522-527, 2016.06.
26. T. Kanzaki, Nagashima Yoshihiko, S. Inagaki, F. Kin, Y. Miwa, M. Sasaki, Takuma Yamada, Fujisawa Akihide, T. Kobayashi, Naohiro Kasuya, Yusuke Kosuga, Sanae-I. Itoh, K. Itoh, Improvement of the Reynolds stress probe for end-plate biasing experiment in a cylindrical laboratory plasma, Plasma and Fusion Research: Rapid Communications, 2016.05.
27. R. Soga, T. Tokuzawa, K. Y Watanabe, K. Tanaka, I. Yamada, S. Inagaki, Naohiro Kasuya, LHD Exp. Group, Developments of frequency comb microwave reflectometer for the interchange mode observations in LHD plasma, JOURNAL OF INSTRUMENTATION, 10.1088/1748-0221/11/02/C02009, 11, 2016.02.
28. S. Inagaki, T. Kobayashi, Yusuke Kosuga, Sanae-I. Itoh, T. Mitsuzono, Nagashima Yoshihiko, H. Arakawa, Takuma Yamada, Y. Miwa, Naohiro Kasuya, Makoto Sasaki, M. Lesur, Fujisawa Akihide, K. Itoh, A Concept of Cross-Ferroic Plasma Turbulence, SCIENTIFIC REPORTS, 10.1038/srep22189, 6, 2016.02.
29. 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.
30. Tatsuya Kobayashi, S. Inagaki, M. Sasaki, Yusuke Kosuga, H. Arakawa, Takuma Yamada, Nagashima Yoshihiko, Y. Miwa, Naohiro Kasuya, Fujisawa Akihide, Sanae-I. Itoh, K. Itoh, 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, 2015.11.
31. K. Itoh, Sanae-I. Itoh, K. Kamiya, Naohiro Kasuya, On the spatial structure of solitary radial electric field at the plasma edge in toroidal confinement devices, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/57/7/075008, 57, 7, 2015.07.
32. Fumiyoshi Kin, Takuma Yamada, Shigeru Inagaki, Hiroyuki Arakawa, Yoshihiko Nagashima, Naohiro Kasuya, Akihide Fujisawa, Kousuke Nakanishi, Hikaru Kono, Takaaki Mizokami, Makoto Sasaki, Maxime Lesur, Yusuke Kosuga, Kimitaka Itoh, Sanae-I. Itoh, Evaluation of Non-Linear Mode Coupling During End-Plate Biasing Experiment in PANTA, Plasma Fusion Research, DOI: 10.1585/pfr.10.3401043, 10, 3401043-1-3401043-4, 2015.04.
33. Naohiro Kasuya, Satoru Sugita, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Simulation study of hysteresis in the gradient-flux relation in toroidal plasma turbulence, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/57/4/044010, 57, 4, 2015.04.
34. G. Hattori, Naohiro Kasuya, M. Yagi, Analysis of Ion-Temperature-Gradient Instabilities Using a Gyro-Fluid Model in Cylindrical Plasmas, Plasma and Fusion Research, DOI: 10.1585/pfr.10.3401060, 10, 2015.04.
35. Makoto Sasaki, Naohiro Kasuya, T. Kobayashi, H. Arakawa, K. Itoh, K. Fukunaga, Takuma Yamada, M. Yagi, Sanae-I. Itoh, Formation mechanism of steep wave front in magnetized plasmas, PHYSICS OF PLASMAS, 10.1063/1.4916490, 22, 3, 2015.03.
36. Shigeru Inagaki, Kimitaka Itoh, Sanae-I. Itoh, Yusuke Kosuga, Maxime Lesur, Naohiro Kasuya, Test of the Telegraph Equation for Transport Dynamics in Plasma, Plasma Fusion Research, DOI: 10.1585/pfr.10.1203002, 10, 1203002-1-1203002-2, 2015.01.
37. Tokihiko Tokuzawa, Shigeru Inagaki, Akira Ejiri, Ryota Soga, Ichihiro Yamada, Shin Kubo, Mikiro Yoshinuma, Katsumi Ida, Chihiro Suzuki, Kenji Tanaka, Tsuyoshi Akiyama, Naohiro Kasuya, Kimitaka Itoh, Kiyomasa Watanabe, Hiroshi Yamada, Kazuo Kawahata, LHD Experiment Group, Ka-band Microwave Frequency Comb Doppler Reflectometer System for the Large Helical Device, Plasma Fusion Research, DOI: 10.1585/pfr.9.1402149, 9, 1402149-1-1402149-6, 2014.12.
38. Takuma Yamada, Shigeru Inagaki, Tatsuya Kobayashi, Yoshihiko Nagashima, Tomohiro Mitsuzono, Yudai Miwa, Kousuke Nakanishi, Hiromitsu Fujino, Makoto Sasaki, Naohiro Kasuya, Maxime Lesur, Yusuke Kosuga, Akihide Fujisawa, Sanae-I. Itoh and Kimitaka Itoh, End plate biasing experiments in linear magnetized plasmas, Nuclear Fusion, 10.1088/0029-5515/54/11/114010, 54, 11, 114010-1-114014-5, 2014.11.
39. Shigeru Inagaki, Tokihiko Tokuzawa, Tatsuya Kobayashi, Sanae-I. Itoh, Kimitaka Itoh, Katsumi Ida, Akihide Fujisawa, Shin Kubo, Takashi Shimozuma, Naoki Tamura, Naohiro Kasuya, Hayato Tsuchiya, Yoshio Nagayama, the LHD Experiment Group, Study of non-linear coupling of fluctuations at long distance in LHD, Nuclear Fusion, 10.1088/0029-5515/54/11/114014, 54, 11, 114014-1-114014-6, 2014.11.
40. Makoto Sasaki, Naohiro Kasuya, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Nonlinear competition of turbulent structures and improved confinement in magnetized cylindrical plasmas, Nuclear Fusion, 10.1088/0029-5515/54/11/114009, 54, 11, 114009-1-114009-9, 2014.11.
41. Naohiro Kasuya, Satoru Sugita, Shigeru Inagaki, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, On violation of local closure of transport relation in high-temperature magnetized plasmas, Physics of Plasmas, 2014.11.
42. Naohiro Kasuya, Makoto Sasaki, S. Inagaki, K. Itoh, M. Yagi, Sanae-I. Itoh, Numerical Diagnostics of Non-Diffusive Transport Process by Use of Turbulence Diagnostic Simulator, 25th IAEA Fusion Energy Conference, 2014.10.
43. Tatsuya Kobayashi, Kimitaka Itoh, Takeshi Ido, Kensaku Kamiya, Sanae-I. Itoh, Yukitoshi Miura, Yoshihiko Nagashima, Akihide Fujisawa, Shigeru Inagaki, Katsumi Ida, Naohiro Kasuya, Katsumichi Hoshino, Dynamics of edge limit cycle oscillation in the JFT-2M Tokamak, Nuclear Fusion, 54, 7, 73017, 2014.07.
44. Shigeru Inagaki, Sanae-I. Itoh, Kimitaka Itoh, Katsumi Ida, Daniel Lopez-Bruna, Maria A. Ochand, Teresa Estrada, Boudewijn Ph. Van Milligen, Carlos Hidalgo, Naohiro Kasuya, TJ-II team, Higher Harmonics in the Perturbative Transport Study in TJ-II ECH Plasma, Plasma Fusion Research, DOI: 10.1585/pfr.9.1202052, 9, 1202052-1-1202052-2, 2014.05.
45. Makoto Sasaki, Naohiro Kasuya, Kimitaka Itoh, Masatoshi Yagi, Sanae-I. Itoh, Dynamical response of turbulent structures in cylindrical magnetized plasmas, JPS Conference Proceedings, 1, 015011-1-015011-5, 2014.03.
46. 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, Kimitaka Itoh, Identification of Quasi-Periodic Nonlinear Waveforms in Turbulent Plasmas, Plasma Fusion Research, 9.0, 1201016.0, 2014.03.
47. Shigeru Inagaki, Kimitaka Itoh, Takuma Yamada, Sanae-I. Itoh, Tokihiko TOKUZAWA, Akihide Fujisawa, Naohiro Kasuya, Makoto Sasaki, Yoshihiko Nagashima, Hiroyuki ARAKAWA, Measurement of Dynamical Density Profiles Using a Microwave Frequency Comb Reflectometer, Plasma Fusion Research, DOI: 10.1585/pfr.8.1201171, 8, 1201171-1-1201171-2, 2013.12.
48. 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, LHD Experiment Group, New Method of Analysis for Dynamical Transport, Plasma Fusion Research, DOI: 10.1585/pfr.8.1202172, 8, 1202172-1-1202172-2, 2013.12.
49. Shigeru Inagaki, T. Tokuzawa, N. Tamura, Sanae-I. Itoh, T. Kobayashi, K. Ida, T. Shimozuma, S. Kubo, K. Tanaka, T. Ido, A. Shimizu, H. Tsuchiya, Naohiro Kasuya, Y. Nagayama, K. Kawahata, S. Sudo, H. Yamada, Akihide Fujisawa, K. Itoh, LHD Experimental Group, How is turbulence intensity determined by macroscopic variables in a toroidal plasma?, NUCLEAR FUSION, 10.1088/0029-5515/53/11/113006, 53, 11, 113006-1-113006-9, 2013.11.
50. Shigeru Inagaki, Sanae-I. Itoh, Kimitaka Itoh, Naohiro Kasuya, T, Kobayashi, Akihide Fujisawa, T. Tokuzawa, K. Ida, S. Kubo, T. SHimozuma, N. Tamura, H. Tsuchiya, Yoshihiko Nagashima, K. Kawahata, H. Yamada, A. Komori, Higher Harmonics in a Perturbative Transport Experiment, Plasma and Fusion Research, DOI: 10.1585/pfr.8.1202172, 8, 1202172-1-1202172-2, 2013.10.
51. Makoto Sasaki, Naohiro Kasuya, M. Yagi, K. Itoh, Yoshihiko Nagashima, Shigeru Inagaki, Sanae-I. Itoh, Statistical Analyses of Turbulent Particle and Momentum Fluxes in a Cylindrical Magnetized Plasma, Plasma and Fusion Research, DOI: 10.1585/pfr.8.2401113, 8, 2401113-1-2401113-5, 2013.09.
52. Yudai Miwa, Naohiro Kasuya, Makoto Sasaki, Shigeru Inagaki, K .Itoh, M. Yagi, Akihide Fujisawa, Yoshihiko Nagashima, Maxime Lesur, T. Kobayashi, S. Yamada, T. Yamashita, S. Otsubo, S. Kakigawa, T. Mitsuzono, H. Fujino, Sanae-I. Itoh, Evaluation of Excitation Conditions of ITG Modes in the PANTA, Plasma and Fusion Research, DOI: 10.1585/pfr.8.2403133, 8, 2403133-1-2403133-5, 2013.09.
53. O Kaneko, H Yamada, S Inagaki, M Jakubowski, S Kajita, S Kitajima, K Koga, T Morisaki, S Morita, T Mutoh, S Sakakibara, Y Suzuki, H Takahashi, K Tanaka, K Toi, Y Yoshimura, T Akiyama, Y Asahi, N Ashikawa, H Chikaraishi, A Cooper, DS Darrow, E Drapiko, P Drewelow, X Du, A Ejiri, M Emoto, T Evans, N Ezumi, K Fujii, T Fukuda, H Funaba, M Furukawa, DA Gates, M Goto, T Goto, W Guttenfelder, S Hamaguchi, M Hasuo, T Hino, Y Hirooka, K Ichiguchi, K Ida, H Idei, T Ido, H Igami, K Ikeda, S Imagawa, T Imai, M Isobe, M Itagaki, T Ito, K Itoh, S Itoh, A Iwamoto, K Kamiya, T Kariya, H Kasahara, N Kasuya, D Kato, T Kato, K Kawahata, F Koike, S Kubo, R Kumazawa, D Kuwahara, S Lazerson, H Lee, S Masuzaki, S Matsuoka, H Matsuura, A Matsuyama, C Michael, D Mikkelsen, O Mitarai, T Mito, J Miyazawa, G Motojima, K Mukai, A Murakami, I Murakami, S Murakami, T Muroga, S Muto, K Nagaoka, K Nagasaki, Y Nagayama, N Nakajima, H Nakamura, Y Nakamura, H Nakanishi, H Nakano, T Nakano, K Narihara, Y Narushima, K Nishimura, S Nishimura, M Nishiura, YM Nunami, T Obana, K Ogawa, S Ohdachi, N Ohno, N Ohyabu, T Oishi, M Okamoto, A Okamoto, M Osakabe, Y Oya, T Ozaki, N Pablant, BJ Peterson, A Sagara, K Saito, R Sakamoto, H Sakaue, M Sasao, K Sato, M Sato, K Sawada, R Seki, T Seki, V Sergeev, S Sharapov, I Sharov, A Shimizu, T Shimozuma, M Shiratani, M Shoji, S Sudo, H Sugama, C Suzuki, K Takahata, Y Takeiri, Y Takemura, M Takeuchi, H Tamura, N Tamura, H Tanaka, T Tanaka, M Tingfeng, Y Todo, M Tokitani, K Tokunaga, T Tokuzawa, H Tsuchiya, K Tsumori, Y Ueda, L Vyacheslavov, KY Watanabe, Extension of operation regimes and investigation of three-dimensional currentless plasmas in the Large Helical Device, Nuclear Fusion, 53.0, 10.0, 104015.0, 2013.09.
54. Naohiro Kasuya, Satoru Sugita, Makoto Sasaki, Shigeru Inagaki, Masatoshi Yagi, Kimitaka Itoh, Sanae-I. Itoh, Evaluation of Spatial Variation of Nonlinear Energy Transfer by Use of Turbulence Diagnostic Simulator, Plasma and Fusion Research, DOI: 10.1585/pfr.8.2403070, 8, 2403070-1-2403070-5, 2013.06, Turbulence Diagnostic Simulator is an assembly of simulation codes to clarify the formation mechanism of turbulent structures by numerical diagnostics in magnetically confined plasmas. Global simulations are carried out using a reduced MHD model of drift-interchange mode in helical plasmas, and time series data of 3-D fluctuation fields are produced. It includes localized modes in their rational surfaces, and broad modes spread in the radial direction. Magnitudes of nonlinear couplings from the convective derivative are evaluated in the nonlinear saturated states. The radial profile shows that there exist strong mode excitation near the center, various modes and nonlinear couplings with higher m modes in the middle radius, small number of propagating modes near the edge, which contribute to the pressure profile modification. For the detection of the different features, combination of several diagnostics is necessary..
55. Takuma Yamada, Makoto Sasaki, Naohiro Kasuya, Yoshihiko Nagashima, Shigeru Inagaki, Tatsuya KOBAYASHI, Masatoshi YAGI, Akihide Fujisawa, Sanae-I. Itoh, Kimitaka Itoh, Streamer Structures in Experiment and Modeling, Plasma Fusion Research, DOI: 10.1585/pfr.8.2401022, 8, 2401022-1-2401022-5, 2013.04.
56. M. Sasaki, K. Itoh, N. Kasuya, K. Hallatschek and S.-I. Itoh, On a Nonlinear Dispersion Effect of Geodesic Acoustic Modes, Plasma Fusion Res., DOI: 10.1585/pfr.8.1403010, 8, 1403010, 2013.02, The nonlinear dispersion relation of the geodesic acoustic modes (GAMs) is investigated for tokamaks with a high safety factor and low magnetic shear. We focus on the Reynolds stress as a nonlinearity, which is truncated at the third order of the GAM amplitude. The real frequency of the GAM is modified according to the phase of the nonlinear force acting on the GAM, which depends on the turbulence decorrelation rate. The nonlinear frequency shift is much larger than that from the finite gyro-radius effects in the linear theory, when the poloidal turbulent E x B velocities are comparable to the diamagnetic drift velocity. Under such circumstances, the group velocity is strongly enhanced and becomes comparable with the radial phase velocity. In addition, the magnitude of the nonlinear effects is also evaluated using experimental parameters..
57. Soutaro Yamada, Shigeru Inagaki, Stella Oldenburger, 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, Kimitaka Itoh, Evaluation of Electron Temperature Fluctuations Using a Conditional Technique, Plasma and Fusion Research, 7.0, 0.0, 2401133, 2012.10.
58. Noriko Ohyama, Akihide Fujisawa, Shigeru Inagaki, Yoshihiko Nagashima, Stella Oldenburger, Tatsuya Kobayashi, Katsuyuki Kawashima, Yuuki Tobimatsu, Tetsuo Yamashita, Soutaro Yamada, Hiroyuki Arakawa, Takuma Yamada, Masatoshi Yagi, Naohiro Kasuya, Makoto Sasaki, Sanae-I Itoh, Kimitaka Itoh, Observations of Intermittent Structures in the Periphery of a Cylindrical Linear Plasma in PANTA, Plasma and Fusion Research, 7.0, 1201025, 2012.04, 2012.04.
59. M. Sasaki, K. Itoh, S.-I. Itoh and N. Kasuya, Zonal flows induced by symmetry breaking with existence of geodesic acoustic modes, Nuclear Fusion, 10.1088/0029-5515/52/2/023009, 52, 2, 023009, 2012.02, The nonlinear dynamics of zonal flows (ZFs) is investigated when geodesic acoustic modes (GAMs) have substantial influence on plasma states. Simultaneous existence of multiple GAMs with different radial phase velocities gives additional nonlinear mode couplings, and asymmetry of the turbulence spectrum induces energy exchanges between GAMs and a ZF. A set of model equations is derived to describe the nonlinear dynamics of a ZF, GAMs and ambient turbulence. The model includes the mechanism of ZF generation by a pair of GAMs, and the back interaction from the turbulence is solved self-consistently. Two stationary solutions are obtained; one is the known solution that the GAM propagates as a travelling wave with no ZF excitation, and the other is a new solution that a pair of GAMs forms a standing wave, which induces a ZF. The accessibility to the steady states, and the threshold for the transition between them are obtained. The GAM and ZF formation in the new state affects the background plasmas. The effects on the turbulent heat diffusivity and the ion heating rate are discussed..
60. H Arakawa, T Kobayashi, S Inagaki, N Kasuya, S Oldenburger, Y Nagashima, T Yamada, M Yagi, A Fujisawa, K Itoh, SI Itoh, Dynamic interaction between a solitary drift wave structure and zonal flows in a linear cylindrical device, Plasma Physics and Controlled Fusion, 53.0, 11.0, 115009.0, 2011.10.
61. Katsuyuki Kawashima, Yasuhiro Miyoshi, Stella Oldenburger, 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, 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, 2406118, 2011.08.
62. Yoshihiko Nagashima, Sanae-I Itoh, Shigeru Inagaki, Hiroyuki Arakawa, Naohiro Kasuya, Akihide Fujisawa, Kunihiro Kamataki, Takuma Yamada, Shunjiro Shinohara, Stella Oldenburger, Masatoshi Yagi, Yuichi Takase, Patrick H Diamond, Kimitaka Itoh, Non-Gaussian properties of global momentum and particle fluxes in a cylindrical laboratory plasma, Physics of Plasmas, 18.0, 7.0, 70701.0, 2011.07.
63. Tatsuya KOBAYASHI, Shigeru INAGAKI, Hiroyuki ARAKAWA, Stella OLDENBURGER, Makoto SASAKI, Yoshihiko NAGASHIMA, Takuma YAMADA, Satoru SUGITA, Masatoshi YAGI, Naohiro KASUYA, Akihide FUJISAWA, Sanae-I ITOH, Kimitaka ITOH, Observation of Nonlinear Coupling between Low Frequency Coherent Modes and Background Turbulence in LMD-U, Plasma and Fusion Research, 6.0, 2401082, 2011.07.
64. Yoshihiko Nagashima, Sanae-I. Itoh, Shigeru Inagaki, Hiroyuki Arakawa, Naohiro Kasuya, Akihide Fujisawa, Non-Gaussian properties of global momentum and particle fluxes in a cylindrical laboratory plasma, PHYSICS OF PLASMAS, 10.1063/1.3601767, 18, 7, 2011.07.
65. N. Kasuya, S. Nishimura, M. Yagi, K. Itoh, and S.-I. Itoh, Heavy Ion Beam Probe Measurement in Turbulence Diagnostic Simulator, Plasma Science and Technology, 13, 3, 326, 2011.03, A numerical measurement module simulating a heavy ion beam probe was developed, and numerical measurements of electrostatic potential and density fluctuations are carried out for 3-D turbulent data generated by a global simulation of drift-interchange mode turbulence in helical plasmas. The deviation between measured and local values is estimated. It is found that the characteristic structures can be detected in spite of the screening effect due to the finite spatial resolution..
66. N. Kasuya, S. Nishimura, M. Yagi, K. Itoh, and S.-I. Itoh, On Detection of a Global Mode Structure in Experiments by Use of Turbulence Diagnostic Simulator, Plasma and Fusion Research, 10.1585/pfr.6.1403002, 6, 1403002, 2011.01, Development of experimental diagnostics in fusion plasmas has made possible to measure plasma fluctuations with high spatial and temporal resolution. To detect a global mode, which contributes to global transport phenomena, it is helpful to use simulation data as a test field for the measurements. The turbulence diagnostic simulator is an assembly of codes for turbulence simulations and numerical diagnostics. Using the turbulence diagnostic simulator, a time series of turbulence data is obtained, on which numerical diagnostics are carried out to demonstrate how global modes to be observed. There exist modes, which are broad in the radial direction, and correlation analyses reveal the characteristic structures with a finite number of local observations in the radial direction, as in experiments..
67. Naohiro Kasuya, MASATOSHI YAGI, Kimitaka Itoh, Sanae-I. Itoh, Selective formation of streamers in magnetized cylindrical plasmas, NUCLEAR FUSION, 10.1088/0029-5515/50/5/054003, 50, 5, 2010.05.
68. Yoshihiko Nagashima, Sanae-I. Itoh, Shunjiro Shinohara, Masayuki Fukao, Akihide Fujisawa, Naohiro Kasuya, Kenichiro Terasaka, Yoshinobu Kawai, George R. Tynan, Patrick H. Diamond, MASATOSHI YAGI, Shigeru Inagaki, Takuma Yamada, Kimitaka Itoh, Coexistence of Zonal Flows and Drift-Waves in a Cylindrical Magnetized Plasma, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 10.1143/JPSJ.77.114501, 77, 11, 2008.11.
69. T. Yamada, S.-I. Itoh, T. Maruta, N. Kasuya, Y. Nagashima, S. Shinohara, K. Terasaka, M. Yagi, S. Inagaki, Y. Kawai, A. Fujisawa, and K. Itoh, Anatomy of Plasma Turbulence, Nature Physics, 10.1038/nphys1029, 4, 9, 721, 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. However, turbulence could generate global structures, such as dynamo magnetic field, zonal flows, 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 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. 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) that should degrade the quality of plasmas for magnetic confinement fusion. 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..
70. N. Kasuya, M. Yagi, K. Itoh, and S.-I. Itoh, Selective Formation of Turbulent Structures in Magnetized Cylindrical Plasmas, Physics of Plasmas, 10.1063/1.2912461, 15, 5, 052302, 2008.05, The mechanism of nonlinear structural formation has been studied with a three-field reduced fluid model, which is extended to describe the resistive drift wave turbulence in magnetized cylindrical plasmas. In this model, ion-neutral collisions strongly stabilize the resistive drift wave, and the formed structure depends on the collision frequency. If the collision frequency is small, modulational coupling of unstable modes generates a zonal flow. On the other hand, if the collision frequency is large, a streamer, which is a localized vortex in the azimuthal direction, is formed. The structure is generated by nonlinear wave coupling and is sustained for a much longer duration than the drift wave oscillation period. This is a minimal model for analyzing the turbulent structural formation mechanism by mode coupling in cylindrical plasmas, and the competitive nature of structural formation is revealed. These turbulent structures affect particle transport..
71. Naohiro Kasuya, MASATOSHI YAGI, Masafumi Azumi, Kimitaka Itoh, Sanae-I. Itoh, Numerical Simulation of Resistive Drift Wave Turbulence in a Linear Device, J. Phys. Soc. Jpn., 2007.04.
72. Naohiro Kasuya, MASATOSHI YAGI, Kimitaka Itoh, Simulation of resistive drift wave turbulence in a linear device, JOURNAL OF PLASMA PHYSICS, 10.1017/S002237780600537X, 72, 957-960, 2006.12.
73. Naohiro Kasuya, K. Itoh, Two-dimensional structure and particle pinch in tokamak H mode, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.94.195002, 94, 19, 2005.05.
74. Naohiro Kasuya, K. Itoh, Y. Takase, Effect of electrode biasing on the radial electric field structure bifurcation in tokamak plasmas, NUCLEAR FUSION, 43, 4, 244-249, 2003.04.