Kyushu University [IDO Takeshi (Professor) Research Institute for Applied Mechanics, Advanced Fusion Research Center]

IDO Takeshi

Last modified date：2022.06.14

Professor / Advanced Fusion Research Center / Research Institute for Applied Mechanics

Papers

1.	Conway, G.D., Smolyakov, A.I., Ido, T., Geodesic acoustic modes in magnetic confinement devices, Nuclear Fusion, https://doi.org/10.1088/1741-4326/ac0dd1, 62, 1, 013001-1-013001-149, vol.62, No.1, 013001, 2022.01, Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature—an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments..
2.	H.R. Fan, T. Ido, A.D. Liu, Min Xu, Z.Y. Liu, Ge Zhuang, L.J. Cai, J.X. Li, L.T. Gao, Chu Zhou, Lin Nie, J.Q. Li, W.D. Liu, Conceptual design of a heavy ion beam probe diagnostic for HL-2M tokamak, Fusion Engineering and Design, 10.1016/j.fusengdes.2021.112845, 173, 112845-112845, 2021.12.
3.	T. Ido, A. Fujisawa, K. Takemura, T.-K. Kobayashi, D. Nishimura, N. Kasuya, A. Fukuyama, C. Moon, K. Yamasaki, S. Inagaki, Y. Nagashima, and T. Yamada, Conceptual design of heavy ion beam probes on the PLATO tokamak, Review of Scientific Instruments , 10.1063/5.0041814, 92, 053553, 2021.05, [URL], Heavy ion beam probe (HIBP) systems have been designed for the new tokamak, PLATO [A. Fujisawa, AIP Conf. Proc. 1993, 020011 (2018)]. The designs have been completed, and the installations are in progress. Two HIBPs are being installed in toroidal sections 180○ apart to investigate long-range correlations in the toroidal direction. Each HIBP consists of an injection beamline and a detection beamline as usual. Yet, one of the HIBPs is equipped with an additional detection beamline; the measurement positions of its two detection beamlines can be placed on almost the same magnetic surface yet at poloidal angles that differ by ∼180○. The use of three detection beamlines allows us to investigate spatial asymmetry and long-range correlations in both the toroidal and poloidal directions, simultaneously. The detected beam intensity is expected to be enough for turbulence measurements in almost the entire plasma region when the electron density is up to 1 × 10^19 m−3 by selecting appropriate ion species for the probe beam. Each detector has three channels 10 mm apart, allowing measurement of local structures of micro-scale turbulence. Therefore, using the HIBPs on the PLATO tokamak will enable both local and global properties of plasma turbulence to be investigated, simultaneously..
4.	Satoru Mori, Taiichi Shikama, Kazuaki Hanada, Nao Yoneda, Arseniy Kuzmin, Masahiro Hasuo, Hiroshi Idei, Takumi Onchi, Akira Ejiri, Yuki Osawa, Yi Peng, Kyohei Matsuzaki, Shinichiro Kado, Keiji Sawada, Takeshi Ido, Kazuo Nakamura, Ryuya Ikezoe, Yoshihiko Nagashima, Makoto Hasegawa, Kengo Kuroda, Aki Higashijima, Takahiro Nagata, Shun Shimabukuro, Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST, ATOMS, 10.3390/atoms8030044, 8, 3, 2020.09, The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved H-delta emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative (CR) model analysis of the emissivity resulted in a ground-state hydrogen atom density of 10(15)-10(16) m(-3) and an ionization degree of 1-0.85 in the plasma..
5.	Takeshi Ido, Abrupt excitation of energetic-particle-driven geodesic acoustic mode in the large helical device, AIP Conference Proceedings, 10.1063/1.5048712, 1993, 020002, 2018.08.
6.	T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Model validation for radial electric field excitation during L-H transition in JFT-2M tokamak, NUCLEAR FUSION, 10.1088/1741-4326/aa5d03, 57, 7, 2017.07, In this paper, we elaborate the electric field excitation mechanism during the L-H transition in the JFT-2M tokamak. Using time derivative of the Poisson's equation, models of the radial electric field excitation is examined. The sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally evaluated radial current that excites the radial electric field. The turbulent Reynolds stress only plays a minor role. The wave convection current that produces a negative current at the edge can be important to explain the ambipolar condition in the L-mode..
7.	T. Ido, K. Itoh, M. Lesur, M. Osakabe, A. Shimizu, K. Ogawa, M. Nishiura, I. Yamada, R. Yasuhara, Y. Kosuga, M. Sasaki, K. Ida, S. Inagaki, S.-I. Itoh and the LHD Experiment Group, Observation of subcritical geodesic acoustic mode excitation in the large helical device, Nuclear Fusion, 10.1088/1741-4326/aa665a, 57, 072009 , 2017.04, The abrupt and strong excitation of the geodesic acoustic mode (GAM) has been found in the large helical device (LHD), when the frequency of a chirping energetic particle-driven GAM (EGAM) approaches twice that of the GAM frequency. The temporal evolution of the phase relation between the abrupt GAM and the chirping EGAM is common in all events. The result indicates a coupling between the GAM and the EGAM. In addition, the nonlinear evolution of the growth rate of the GAM is observed, and there is a threshold in the amplitude of the GAM for the appearance of nonlinear behavior. A threshold in the amplitude of the EGAM for the abrupt excitation of the GAM is also observed. According to one theory (Lesur et al 2016 Phys. Rev. Lett. 116 015003, Itoh et al 2016 Plasma Phys. Rep. 42 418) the observed abrupt phenomenon can be interpreted as the excitation of the subcritical instability of the GAM. The excitation of a subcritical instability requires a trigger and a seed with sufficient amplitude. The observed threshold in the amplitude of the GAM seems to correspond with the threshold in the seed, and the threshold in the amplitude of the EGAM seems to correspond with the threshold in the magnitude of the trigger. Thus, the observed threshold supports the interpretation that the abrupt phenomenon is the excitation of a subcritical instability of the GAM..
8.	2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device © 2016 Author(s).Two-dimensional spatial profiles of potential fluctuation were measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). For 2D spatial profile measurements, the probe beam energy has to be changed, which requires the adjustment of many deflectors in the beam transport line to optimize the beam trajectory, since the transport line of LHD-HIBP system is long. The automatic beam adjustment system was developed, which allows us to adjust the beam trajectory easily. By analyzing coherence between potential fluctuation and magnetic probe signal, the noise level of the mode power spectrum of the potential fluctuation can be reduced. By using this method, the 2D spatial profile of potential fluctuation profile was successfully obtained..
9.	Resistive interchange mode destabilized by helically trapped energetic ions and its effects on energetic ions and bulk plasma in a helical plasma © 2016 IAEA, Vienna. A resistive interchange mode of the structure (, : poloidal and toroidal mode numbers, respectively) with a bursting character and rapid frequency chirping in the range less than 10 kHz is observed for the first time in the edge region of the net current-free, low beta LHD (Large Helical Device) plasmas during high power injection of perpendicular neutral beams. The mode resonates with the precession motion of helically trapped energetic ions (EPs), following the resonant condition. The radial mode structure is recognized to be similar to that of the pressure-driven resistive interchange mode, of which radial displacement eigenfunction quite localizes around the mode rational surface, and evolves into an odd-type (or island-type) during the late of frequency chirping phase. This beam driven mode is excited when the beta value of helically trapped EPs exceeds a certain threshold. This instability is thought to be a new branch of resistive interchange mode destabilized by the trapped energetic ions. The radial transport, i.e. redistribution and losses, of helically trapped energetic ions induced by the mode transiently generates significant radial electric field near the plasma peripheral region. The large shear of thus generated radial electric field is thought to contribute to the observed suppression of micro-turbulence and transient increases of the temperature of fully ionized carbon impurity ions and electron density, suggesting improvement of bulk plasma confinement..
10.	T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas, Scientific Reports, 10.1038/srep30720, 6, 2016.08, Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt "radial" electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson's equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude..
11.	Nonlinear excitation of subcritical fast ion-driven modes © 2016 IAEA, Vienna.In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities..
12.	T. Ido, K. Itoh, M. Osakabe, M. Lesur, A. Shimizu, K. Ogawa, K. Toi, M. Nishiura, S. Kato, M. Sasaki, K. Ida, S. Inagaki, S.-I. Itoh, the LHD Experiment Group, Strong Destabilization of Stable Modes with a Half-Frequency Associated with Chirping Geodesic Acoustic Modes in the Large Helical Device, Physical Review Letters, 10.1103/PhysRevLett.116.015002, 116, 015002, 2016.01, Abrupt and strong excitation of a mode has been observed when the frequency of a chirping energetic-particle driven geodesic acoustic mode (EGAM) reaches twice the geodesic acoustic mode (GAM) frequency. The frequency of the secondary mode is the GAM frequency, which is a half-frequency of the primary EGAM. Based on the analysis of spatial structures, the secondary mode is identified as a GAM. The phase relation between the secondary mode and the primary EGAM is locked, and the evolution of the growth rate of the secondary mode indicates nonlinear excitation. The results suggest that the primary mode (EGAM) contributes to nonlinear destabilization of a subcritical mode..
13.	M. Lesur, K. Itoh, T. Ido, M. Osakabe, K. Ogawa, A. Shimizu, M. Sasaki, K. Ida, S. Inagaki, S. -I. Itoh, Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.116.015003, 116, 1, 2016.01, In a collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase space. However, nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which is significantly below the threshold, but can still grow by (and only by) the collaboration of fluid and kinetic nonlinearities. By modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations, it is shown that this new kind of subcritical instability can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. The model is applied to the bursty onset of geodesic acoustic modes in a LHD experiment. The model recovers several key features such as relative amplitude, time scales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, driven by this mechanism of combined fluid and kinetic nonlinearities..
14.	K. Itoh, T. Kobayashi, T. Ido, S-I Itoh, K. Kamiya, Contribution of geodesic acoustic modes in the limit cycle oscillation near H-mode transition in JFT-2M plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/57/9/092001, 57, 9, 2015.09, The magnitude of geodesic acoustic modes (GAMs) is analyzed, which are driven by the oscillating Reynolds stress force in poloidal direction in the limit cycle oscillation (LCO) of tokamaks near the condition of H-mode transition. Although the frequency of LCO is much lower than the natural frequency, the forced oscillation of GAMs at the LCO frequency is excited. The amplitude of excited GAMs can be similar to that of low frequency zonal flows. The result is compared with the observation of the JFT-2M tokamak..
15.	T. Ido, M. Osakabe, A. Shimizu, T. Watari, M. Nishiura, K. Toi, K. Ogawa, K. Itoh, I. Yamada, R. Yasuhara, Y. Yoshimura, S. Kato and The LHD Experiment Group, Identification of the energetic-particle driven GAM in the LHD, Nuclear Fusion, 10.1088/0029-5515/55/8/083024, 55, 083024, 2015.07, [URL], n = 0 modes with frequency chirping have been observed by a heavy ion beam probe and Mirnov coils in the large helical device plasmas, where n is the toroidal mode number. The spatial structures of the electrostatic potential fluctuation and the density fluctuation correspond to those of the geodesic acoustic mode (GAM). The modes are observed only during the tangential neutral beam injection with the energy of 175 keV. The energy spectra of fast ions measured by a neutral particle analyzer implies that the modes are excited by the fast ions through the inverse Landau damping. The absolute values and the temperature dependence of the frequency of the mode can be interpreted by the dispersion relation taking into account the measured energy spectra of the fast ions. Therefore, the observed n = 0 modes are identified as the energetic-particle driven GAM..
16.	T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Edge plasma dynamics during L-H transition in the JFT-2M tokamak, NUCLEAR FUSION, 10.1088/0029-5515/55/6/063009, 55, 6, 2015.06, This article presents a radial electric field measurement by a heavy ion beam probe in the JFT-2M tokamak, during the L-H transition. An abrupt increase (time scale of O(100 mu s)) of the strong edge radial electric field (localized in the radius with FWHM similar to 7 mm) results in the increase of density gradient and turbulence reduction. Rapid inward propagation of the turbulence suppression front is observed at the transition. After the transition, the electric field structure in the tiny edge localized modes (ELMs) is analyzed. Transport self-regulation events observed in the vicinity of the L-H transition, i.e. the limit cycle oscillation (LCO) in the L-mode, the tiny ELM in the H-mode, as well as the L-H transition itself, are summarized in a single Lissajous diagram in the electric field-density gradient space, which provides a comprehensive explanation of the transition dynamics..
17.	Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, K. Ida, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, Microtearing mode (MTM) turbulence in JIPPT-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/55/4/043008, 55, 4, 2015.04, Magnetic, density and potential fluctuations up to 500 kHz at several spatial points have been observed in the core region of JIPPT-IIU tokamak plasmas using a heavy ion beam probe. The frequency spectra of the density and magnetic oscillations are found to be similar, whereas there are large differences in the phase, coherence and frequency dependences deduced from signals at adjacent sample volumes. These differences allow us to ascribe the detected magnetic fluctuations to the microtearing mode (MTM) by simple dispersion relations of the MTM in collisionless and intermediate regimes. The frequency-integrated level of magnetic fluctuations around 150 kHz (100-200 kHz) is (B) over tilde (r)/B-t approximate to 1 x 10(-4), a level high enough for the ergodization of the magnetic surface and enhanced electron heat loss as derived by Rechester and Rosenbluth (1978 Phys. Rev. Lett. 40 38). This level is consistent with the measurements performed using cross-polarization scattering of microwaves in the Tore Supra tokamak. Our results are the first direct experimental verification of the MTM in the core region of tokamak plasmas, which has been recently observed in gyrokinetic simulations using a very fine mesh in tokamak and ST plasmas..
18.	Resistive interchange modes destabilized by helically trapped energetic ions in a helical plasma © 2015 American Physical Society. A new bursting m=1/n=1 instability (m,n: poloidal and toroidal mode numbers) with rapid frequency chirping down has been observed for the first time in a helical plasma with intense perpendicular neutral beam injection. This is destabilized in the plasma peripheral region by resonant interaction between helically trapped energetic ions and the resistive interchange mode. A large radial electric field is induced near the edge due to enhanced radial transport of the trapped energetic ions by the mode, and leads to clear change in toroidal plasma flow, suppression of microturbulence, and triggering an improvement of bulk plasma confinement..
19.	A. Shimizu, T. Ido, M. Kurachi, R. Makino, M. Nishiura, S. Kato, A. Nishizawa, Y. Hamada, 2D potential measurements by applying automatic beam adjustment system to heavy ion beam probe diagnostic on the Large Helical Device, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.4891975, 85, 11, 2014.11, Two-dimensional potential profiles in the Large Helical Device (LHD) were measured with heavy ion beam probe (HIBP). To measure the two-dimensional profile, the probe beam energy has to be changed. However, this task is not easy, because the beam transport line of LHD-HIBP system is very long (similar to 20 m), and the required beam adjustment consumes much time. To reduce the probe beam energy adjustment time, an automatic beam adjustment system has been developed. Using this system, required time to change the probe beam energy is dramatically reduced, such that two-dimensional potential profiles were able to be successfully measured with HIBP by changing the probe beam energy shot to shot. (C) 2014 AIP Publishing LLC..
20.	S. Inagaki, T. Tokuzawa, N. Tamura, S. -I. Itoh, T. Kobayashi, K. Ida, T. Shimozuma, S. Kubo, K. Tanaka, T. Ido, A. Shimizu, H. Tsuchiya, N. Kasuya, Y. Nagayama, K. Kawahata, S. Sudo, H. Yamada, A. Fujisawa, K. Itoh, How is turbulence intensity determined by macroscopic variables in a toroidal plasma?, NUCLEAR FUSION, 10.1088/0029-5515/53/11/113006, 53, 11, 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..
21.	T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, 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, 3, 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..
22.	Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, Regions of kinetic geodesic acoustic modes and streamers in JIPPT-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/52/6/063023, 52, 6, 2012.06, The radial extent of kinetic geodesic acoustic modes (KGAMs) and streamers is measured using a heavy ion beam probe. Intense KGAM oscillations are observed in the core region of a low-density ohmic (OH) plasma where T-e >> T-i and outside this region, streamers characterized by steepening fronts are observed. The radial profile of plasma density stays flat in the region of the streamers, showing a rise in the plasma density in two regions, one at the scrape-off layer and the other in the core region during the radial scan of sample volumes. Intense (up to e Phi / kT(e) similar to 0.1) and broad GAM oscillations (delta f / f similar to 0.5) are observed in the r < a(p)/2 region of tokamak plasmas. GAM oscillations and streamers are strongly reduced in the heated phase. In addition, the radial profile of the spectra of GAM in the heated phase is very different from that of a low-density OH plasma. The streamers and the two-step rise in the density radial profile disappear in the heated phase..
23.	Long range temperature fluctuation in LHD 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 ~ 1-3kHz, ballistic radial propagation (at a speed of ~1km/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. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research..
24.	A New Simulation Method of Geodesic Acoustic Mode in Toroidal Plasmas by Using Band-Limited White Noise in a δf Neoclassical Transport Code.
25.	S. Inagaki, T. Tokuzawa, K. Itoh, K. Ida, S. -I. Itoh, N. Tamura, S. Sakakibara, N. Kasuya, A. Fujisawa, S. Kubo, T. Shimozuma, T. Ido, S. Nishimura, H. Arakawa, T. Kobayashi, K. Tanaka, Y. Nagayama, K. Kawahata, S. Sudo, H. Yamada, A. Komori, Observation of Long-Distance Radial Correlation in Toroidal Plasma Turbulence, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.107.115001, 107, 11, 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..
26.	K. Nagaoka, K. Ida, M. Yoshinuma, Y. Takeiri, M. Yokoyama, S. Morita, K. Tanaka, T. Ido, A. Shimizu, N. Tamura, H. Funaba, S. Murakami, M. Goto, H. Takahashi, C. Suzuki, Y. Suzuki, K. Ikeda, M. Osakabe, K. Tsumori, H. Nakano, O. Kaneko, H. Yamada, Heat and momentum transport of ion internal transport barrier plasmas on the Large Helical Device, NUCLEAR FUSION, 10.1088/0029-5515/51/8/083022, 51, 8, 2011.08, The peaked ion-temperature profile with steep gradient, the so-called ion internal transport barrier (ion ITB), was formed in the neutral beam heated plasmas on the Large Helical Device and the high-ion-temperature regime of helical plasmas has been significantly extended. The ion thermal diffusivity in the ion ITB plasma decreases down to the neoclassical transport level. The heavy ion beam probe observed the smooth potential profile with negative radial electric field (ion root) in the core region where the ion thermal diffusivity decreases significantly. The large toroidal rotation was also observed in the ion ITB core and the transport of toroidal momentum was analysed qualitatively. The decrease in momentum diffusivity with ion temperature increase was observed in the ion ITB core. The toroidal rotation driven by ion-temperature gradient, the so-called intrinsic rotation, is also identified..
27.	Fabrication of the measurement system for the cross sections in collisions between Au beams and gas targets.
28.	T. Ido, A. Shimizu, M. Nishiura, S. Nakamura, S. Kato, H. Nakano, Y. Yoshimura, K. Toi, K. Ida, M. Yoshinuma, S. Satake, F. Watanabe, S. Morita, M. Goto, K. Itoh, S. Kubo, T. Shimozuma, H. Igami, H. Takahashi, I. Yamada, K. Narihara and the LHD Experiment Group, Potential ﬂuctuation associated with the energetic-particle-induced geodesic acoustic mode in the Large Helical Device, Nuclear Fusion, 10.1088/0029-5515/51/7/073046, 51, 073046, 2011.06, [URL], Geodesic acoustic modes (GAM) driven by energetic particles are observed in the Large Helical Device (LHD) by a heavy ion beam probe. The GAM localizes near the magnetic axis. It is conﬁrmed that the energetic-particle-induced GAM is accompanied by an electrostatic potential ﬂuctuation and radial electric ﬁeld ﬂuctuation. The amplitude of the potential ﬂuctuation is several hundred volts, and it is much larger than the potential ﬂuctuation associated with turbulence-induced GAMs observed in the edge region in tokamak plasmas. The energetic-particle-induced GAM modulates the amplitude of the density ﬂuctuation in a high-frequency range. The observed GAM frequency is constant at the predicted GAM frequency in plasmas with reversed magnetic shear. On the other hand, it shifts upwards from the predicted GAM frequency in plasmas with monotonic magnetic shear..
29.	Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, K. Ida, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, Detection of the kinetic geodesic acoustic mode (KGAM) near the centre region of JIPPT-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/51/3/033005, 51, 3, 2011.03, The broad and intense spectrum of the geodesic acoustic mode (GAM) oscillations near the magnetic axis of tokamak plasmas with T-e/T-i >> 1 becomes narrow and weak during neutral beam heating. It then becomes wide and weak during third harmonics ICRF heating. The wide spectra of GAMs are generally consistent with recent kinetic GAM (KGAM) theories..
30.	Production of Sub-MeV Positive Gold Ion Beams with Various Gas Targets to Improve the Tandem Accelerator of the LHD-HIBP.
31.	K. Toi, F. Watanabe, T. Tokuzawa, K. Ida, S. Morita, T. Ido, A. Shimizu, M. Isobe, K. Ogawa, D. A. Spong, Y. Todo, T. Watari, S. Ohdachi, S. Sakakibara, S. Yamamoto, S. Inagaki, K. Narihara, M. Osakabe, K. Nagaoka, Y. Narushima, K. Y. Watanabe, H. Funaba, M. Goto, K. Ikeda, T. Ito, O. Kaneko, S. Kubo, S. Murakami, T. Minami, J. Miyazawa, Y. Nagayama, M. Nishiura, Y. Oka, R. Sakamoto, T. Shimozuma, Y. Takeiri, K. Tanaka, K. Tsumori, I. Yamada, M. Yoshinuma, K. Kawahata, A. Komori, Observation of reversed-shear Alfvén eigenmodes excited by energetic ions in a helical plasma, Physical Review Letters, 10.1103/PhysRevLett.105.145003, 105, 14, 2010.10, Reversed-shear Alfvén eigenmodes were observed for the first time in a helical plasma having negative q0′′ (the curvature of the safety factor q at the zero shear layer). The frequency is swept downward and upward sequentially via the time variation in the maximum of q. The eigenmodes calculated by ideal MHD theory are consistent with the experimental data. The frequency sweeping is mainly determined by the effects of energetic ions and the bulk pressure gradient. Coupling of reversed-shear Alfvén eigenmodes with energetic ion driven geodesic acoustic modes generates a multitude of frequency-sweeping modes. © 2010 The American Physical Society..
32.	A. Shimizu, T. Ido, S. Nakamura, K. Toi, M. Nishiura, S. Kato, Potential measurements with heavy ion beam probe system on LHD, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.3491317, 81, 10, 2010.10, The heavy ion beam probe system in the Large Helical Device (LHD) was improved as follows. At first, the additional new sweeper was installed into the diagnostic port to extend the observable region. By using this sweeper, the potential profile was measured in a wider minor radius range than in previous experiments, in the case of outward shifted magnetic configuration of LHD. Next, the real time control system was installed to control the probe beam orbit for measuring the potential in plasma with large plasma current. In this system, a digital signal processor was used to control the probe beam in real time. The system worked well in the fixed position observation mode. In the sweeping mode for profile measurement, this control system became unstable. The details of this system and the experimental results are reported in this article. (c) 2010 American Institute of Physics. [doi:10.1063/1.3491317].
33.	T Ido, A Shimizu, M Nishiura, K Nagaoka, M Yokoyama, K Ida, M Yoshinuma, K Toi, K Itoh, H Nakano, S Nakamura, F Watanabe, S Satake, Y Yoshimura, M Osakabe, K Tanaka, T Tokuzawa, Y Takeiri, K Tsumori, K Ikeda, S Kubo, T Shimozuma, H Igami, H Takahashi, N Tamura and LHD Experiment Group, Experimental study of radial electric ﬁeld and electrostatic potential ﬂuctuation in the Large Helical Device, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/52/12/124025, 52, 124025, 2010.09, [URL], A heavy ion beam probe was installed on the Large Helical Device (LHD) to investigate the roles of radial electric ﬁelds (Er ) in magnetically conﬁned high-temperature plasmas. Two new observations are presented. One is the observation of electrostatic potential proﬁles during the formation of extremely hollow density proﬁles of impurities, called the impurity hole (Ida K et al 2009 Phys. Plasmas 16 056111), in the LHD plasmas. The measured Er is negative, and the Er determined by the ambipolarity condition of neoclassical particle ﬂuxes is consistent with this observation. However, the transport analysis indicates that the formation of the extremely hollow proﬁle is not attributable to the impurity ﬂuxes driven by Er and the density and temperature gradients of the impurity. The other new observation is on the geodesic acoustic mode (GAM). The electrostatic potential ﬂuctuation associated with the GAM, which is probably induced by energetic particles, in plasmas with the reversed or weak magnetic shear is identiﬁed. The GAM is localized in the core region of the plasma..
34.	Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, GAM generation by drift waves in JIPP T-llU tokamak core plasmas, NUCLEAR FUSION, 10.1088/0029-5515/50/2/025001, 50, 2, 2010.02, Density and potential fluctuations were measured in the core region of the JIPP-TIIU plasma using a heavy ion beam probe. By applying a new technique of wavenumber resolved bicoherence, the coupling of the drift waves with zonal flows was clearly observed. In addition, nonlinear energy flow from drift-wave turbulence to high-frequency zonal flows using Ritz's model equation was first observed in the core region of low-density tokamak plasmas, which means there is generation of GAM by drift waves. The nonlinear growth rate of high-frequency zonal flow was estimated to be in the order of 10(4) s(-1) or higher. In additionally heated plasmas where low-frequency ion temperature gradient mode is dominant, the bicoherence pattern changes drastically..
35.	Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano, Shinji Kato, Shinsuke Ohshima, Yasuo Yoshimura, Shin Kubo, Takashi Shimozuma, Hiroe Igami, Hiromi Takahashi, Kazuo Toi, Fumitake Watanabe, Kazumichi Narihara and Ichihiro Yamada, Development of a heavy ion beam probe for measuring electrostatic potential profile and its fluctuation in LHD, Plasma Science and Technology, 10.1088/1009-0630/11/4/19, 11, 460-464, 2009.08.
36.	T. IDO, A. SHIMIZU, M. NISHIURA, S. KATO, H. NAKANO, S. OHSHIMA, M. YOKOYAMA, S. MURAKAMI, A. WAKASA, S. NAKAMURA, M. YOKOTA, K. TSUKADA, H. OGAWA, T. INOUE, and LHD EXPERIMENT GROUP, DEVELOPMENT OF 6-MeV HEAVY ION BEAM PROBE ON LHD, Fusion Science and Technology, 10.13182/FST10-A10829, 58, 436, 2009.07, [URL], A heavy–ion beam probe (HIBP) using a 3-MV tandem accelerator was installed in Large Helical Device (LHD). It is designed to measure the electrostatic potential in the core region directly. The electrostatic potential profiles can be measured successfully using the HIBP,and the radial electric field predicted by the neoclassical theory is consistent with that measured using the HIBP as long as the ambipolarity condition of the neoclassical particle flux has a single solution. Although the turbulent fluctuation is not detected because of low signal-to-noise ratio, several coherent fluctuations, which are inferred to be reversed-shear-induced Alfvén eigenmode and the geodesic acoustic mode, are observed directly in core plasmas, and the spatial distribution is revealed..
37.	KANEKO Osamu, EMOTO Masahiko, FUNABA Hisamichi, GONCHAROV Pavel, GOTO Motoshi, GOTO Takuya, HAMAGUCHI Shinji, ICHIGUCHI Katsuji, IDO Takeshi, IGAMI Hiroe, IKEDA Katsunori, YOKOYAMA Masayuki, IMAGAWA Shinsaku, ISOBE Mitsutaka, ITOH Kimitaka, IWAMOTO Akifumi, KANNO Ryutaro, KASAHARA Hiroshi, KASUYA Naohiro, KATO Daiji, KAWAHATA Kazuo, KOBAYASHI Masahiro, YOSHINUMA Mikiro, KUBO Shin, KUMAZAWA Ryuhei, MAEKAWA Ryuji, MASUZAKI Suguru, MITO Toshiyuki, MIYAZAWA Jun-ichi, MIZUGUCHI Naoki, MORISAKI Tomohiro, MORITA Shigeru, MOTOJIMA Gen, NAGAOKA Ken-ichi, MUTO Sadatsugu, MUTOH Takashi, NAGAYAMA Yoshio, NAKAJIMA Noriyoshi, NAKAMURA Yukio, NAKANISHI Hideya, NARIHARA Kazumichi, NARUSHIMA Yoshiro, NISHIMURA Kiyohiko, NISHIURA Masaki, IDA Katsumi, OBANA Tetsuhiro, OHDACHI Satoshi, OHYABU Nobuyoshi, OSAKABE Masaki, OZAKI Tetsuo, PETERSON Byron J, SAGARA Akio, SAITO Kenji, SAKAKIBARA Satoru, SATAKE Shinsuke, SAKAMOTO Ryuichi, SATO Kuninori, SEKI Tetsuo, SHIMIZU Akihiro, SHIMOZUMA Takashi, SHOJI Mamoru, SUDO Shigeru, SUGAMA Hideo, SUZUKI Chihiro, SUZUKI Yasuhiro, TAKAHASHI Hiromi, AKIYAMA Tsuyoshi, TAKAHATA Kazuya, TAKEIRI Yasuhiko, TAMURA Hitoshi, TAMURA Naoki, TANAKA Kenji, TODA Shinichiro, TOI Kazuo, TOKITANI Masayuki, TOKUZAWA Tokihiko, TSUMORI Katsuyoshi, ASHIKAWA Naoko, WATANABE Kiyomasa, YAMADA Ichihiro, YAMADA Hiroshi, YAMAGISHI Osamu, YANAGI Nagato, YOSHIMURA Shinji, YOSHIMURA Yasuo, KOMORI Akio, CHIKARAISHI Hirotaka, Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma, Plasma and Fusion Research, 10.1585/pfr.4.027, 4, 27-27, 2009.01, Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 × 10²¹ m^-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (R_ax), and the steepest profile is obtained at R_ax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 × 10¹⁹ m^-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around R_ax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor..
38.	Shinsuke Ohshima, Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano, Measurements of spatial structure of plasma potential and density fluctuations by multichannel heavy ion beam probe on large helical device, Review of Scientific Instruments, 10.1063/1.2981177, 79, 10, 10F320, 2008.10.
39.	Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano, Shinsuke Ohshima, Shinji Kato, Yasuji Hamada, Yasuo Yoshimura, Shin Kubo, Takashi Shimozuma, Hiroe Igami, Hiromi Takahashi, Kazuo Toi, and Fumitake Watanabe, Measurement of Electrostatic Potential Fluctuation using Heavy Ion Beam Probe in Large Helical Device, Review of Scientific Instruments, 10.1063/1.2971207, 79, 10F318, 2008.07, Heavy ion beam probe (HIBP) for large helical device (LHD) has been improved to measure the potential fluctuation in high-temperature plasmas. The spatial resolution is improved to about 10 mm by controlling the focus of a probe beam. The HIBP is applied to measure the potential fluctuation in plasmas where the rotational transform is controlled by electron cyclotron current drive. The fluctuations whose frequencies change with the time constant of a few hundreds of milliseconds and that with a constant frequency are observed. The characteristics of the latter fluctuation are similar to those of the geodesic acoustic mode oscillation. The spatial profiles of the fluctuations are also obtained..
40.	A. Fujisawa, K. Itoh, A. Shimizu, H. Nakano, S. Ohshima, H. Iguchi, K. Matsuoka, S. Okamura, T. Minami, Y. Yoshimura, K. Nagaoka, K. Ida, K. Toi, C. Takahashi, M. Kojima, S. Nishimura, M. Isobe, C. Suzuki, T. Akiyama, T. Ido, Y. Nagashima, S. -I. Itoh, P. H. Diamond, Experimental studies of zonal flow and field in compact helical system plasma, PHYSICS OF PLASMAS, 10.1063/1.2889012, 15, 5, 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..
41.	Takeshi IDO, Akihiro SHIMIZU, Masaki NISHIURA, Shinji KATO, Haruhisa NAKANO, Akimitsu NISHIZAWA, Yasuji HAMADA, Mitsuhiro YOKOTA, Kiwamu TSUKADA, Hideki OGAWA, Tomoyuki INOUE, Katsumi IDA, Mikiro YOSHINUMA, Sadayoshi MURAKAMI, Kenji TANAKA, Kazumichi NARIHARA, Ichihiro YAMADA, Kazuo KAWAHATA, Naoki TAMURA and the LHD Experimental Group, Electrostatic Potential Measurement by Using 6-MeV Heavy Ion Beam Probe on LHD, Plasma and Fusion Research, 10.1585/pfr.3.031, 3, 031, 2008.04, [URL], A heavy ion beam probe (HIBP) using a 3 MV tandem accelerator was installed in Large Helical Device (LHD). It is designed to measure the electrostatic potential in the core region directly. It is calibrated and can be used to measure the electrostatic potential proﬁles in LHD plasmas. The radial electric ﬁeld (Er) obtained from the potential proﬁles measured using the HIBP agrees with that measured by charge exchange spectroscopy (CXS). Er predicted by the neoclassical theory is also compared to that measured using the HIBP, and is in good agreement with the experimental results in the core region..
42.	Status of the heavy ion beam probe system in the Large Helical Device A heavy ion beam probe (HIBP) system has been installed into the Large Helical Device (LHD) to measure the spatial profile of the plasma potential and density fluctuations. The optimization of the HIBP system, especially the beam injector, is described. The negative ion beam is required for the MeV beam production in a tandem accelerator. A sputter-type heavy negative ion source has been developed as an intense Au- beam source to produce Au+ beams with energy in the MeV range. The extraction electrodes and the Einzel lens system of the ion source have been designed taking into account the beam optics, and installed into the real machine. Throughout the plasma diagnostics on LHD experiments, the consumptions of vaporized caesium and gold target are being characterized for practical operations. In addition, the experimental charge fractions are compared with the theoretical fractions for understanding the charge-changing behavior of Au- ions and optimizing the fraction of Au+ ions at the exit of the tandem accelerator of the HIBP system. © 2008 American Institute of Physics..
43.	Experimental progress on zonal flow physics in toroidal plasmas The present status of experiments on zonal flows in magnetic confinement experiments is examined. The innovative use of traditional and modern 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. © 2007 IAEA..
44.	Y. Nagashima, K. Itoh, S-I Itoh, A. Fujisawa, M. Yagi, K. Hoshino, K. Shinohara, A. Ejiri, Y. Takase, T. Ido, K. Uehara, Y. Miura, In search of zonal flows by using direct density fluctuation measurements, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/10/002, 49, 10, 1611-1625, 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..
45.	T. IDO, A. SHIMIZU, M. NISHIURA, Y. HAMADA, S. KATO, A. NISHIZAWA, H. NAKANO, Spatial resolution of the heavy ion beam probe on LHD, Plasma and Fusion Research, 10.1585/pfr.2.S1100, 2, S1100, 2007.03.
46.	A. Fujisawa, A. Shimizu, H. Nakano, S. Ohshima, K. Itoh, Y. Nagashima, S. -I Itoh, H. Iguchi, Y. Yoshimura, T. Minami, K. Nagaoka, C. Takahashi, M. Kojima, S. Nishimura, M. Isobe, C. Suzuki, T. Akiyama, T. Ido, K. Matsuoka, S. Okamura, P. H. Diamond, Intermittent characteristics in coupling between turbulence and zonal flows, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/3/002, 49, 3, 211-217, 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..
47.	T. Ido, A. Shimizu, M. Nishiura, A. Nishizawa, S. Katoh, K. Tsukada, M. Yokota, H. Ogawa, T. Inoue, Y. Hamada, T. P. Crowley, LHD Experimental Group , 6 MeV heavy ion beam probe on Large Helical Device, Review of Scientific Instruments, 10.1063/1.2338311, 77, 10F523, 2006.10, A heavy ion beam probe (HIBP) has been installed on the Large Helical Device (LHD). A MeV-range beam is required for the LHD-HIBP. The probing beam is accelerated up to 6 MeV by use of a tandem accelerator. A new energy analyzer with tandem electrodes has also been developed to analyze such a high energy beam. As a result, a secondary beam can be detected and its energy successfully analyzed. It is verified, in principle, that the potential profile can be measured using the HIBP. .
48.	A Fujisawa, A Shimizu, H Nakano, S Ohsima, K Itoh, H Iguchi, Y Yoshimura, T Minami, K Nagaoka, C Takahashi, M Kojima, S Nishimura, M Isobe, C Suzuki, T Akiyama, Y Nagashima, K Ida, K Toi, T Ido, SI Itoh, K Matsuoka, S Okamura, PH Diamond, Turbulence and transport characteristics of a barrier in a toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S15, 48, 4, S205-S212, 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..
49.	Y. Hamada, T. Watari, A. Nishizawa, T. Ido, M. Kojima, Y. Kawasumi, K. Toi, Wavelet and Fourier analysis of zonal flows and density fluctuations in JIPP T-IIU tokamak plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S13, 48, 4, S177-S191, 2006.04, Wavelet and two-dimensional Fourier analyses of local potential and density signals were conducted. These signals were obtained in the core region of tokamak plasmas by a multiple-sample-volume heavy ion beam probe. In the low-density Ohmic plasma where the electron temperature is much higher than that of the ions, the high-frequency (HF) zonal flow in geodesic acoustic mode frequency region is more energetic than the low-frequency zonal flow from 10 to 1000Hz in terms of integrated intensity. This result is in sharp contrast to the results of ITG simulations, of the tokamak plasmas. The HF zonal flow has a short lifetime, (a few cycles). The wavelet spectra of density are much,more chaotic than those of potential turbulence, changing the amplitude and frequency of the dominant modes more rapidly within the lifetime of the HF zonal flows. It, was. also found that HF parts of the density fluctuations are highly modulated by the HF zonal flows..
50.	T Ido, Y Miura, K Kamiya, Y Hamada, K Hoshino, A Fujisawa, K Itoh, S-I Itoh, A Nishizawa, H Ogawa, Y Kusama and JFT-2M group, Geodesic–acoustic-mode in JFT-2M tokamak plasmas, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/48/4/S04, 48, S41, 2006.03, [URL], 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˜r,GAM) and the amplitude of the density ﬂuctuation indicates that the modulation of the ambient density ﬂuctuation delays the E˜r,GAM. The causality between the GAM and the modulation of the density ﬂuctuation is revealed..
51.	T. Ido, Y. Miura, K. Hoshino, K. Kamiya, Y. Hamada, A. Nishizawa, Y. Kawasumi, H. Ogawa, Y. Nagashima, K. Shinohara, Y. Kusama, JFT-2M group, Observation of the interaction between the geodesic acoustic mode and ambient ﬂuctuation in the JFT-2M tokamak, Nuclear Fusion, 10.1088/0029-5515/46/5/003, 46, 5, 512, 2006.03, [URL], The electrostatic and density ﬂuctuation are measured simultaneously with a heavy ion beam probe. The electrostatic ﬂuctuation with the geodesic acoustic mode (GAM) frequency is observed in L-mode plasmas and not in H-mode plasmas. The poloidal and radial structure is consistent with the GAM. So the ﬂuctuation is concluded to be the GAM. The amplitude of the GAM changes in the radial direction; it is small near the separatrix, has a maximum at 3 cm inside the separatrix and decreases again to 5 cm inside the separatrix. The GAM and the temporal behaviour of the ambient density ﬂuctuation show a signiﬁcant coherence, and the phase of modulation of the ambient density ﬂuctuation tends to delay the potential oscillation of the GAM. It is clearly veriﬁed that the GAM affects ambient ﬂuctuation and also the local particle transport through modulation of the amplitude of the ambient ﬂuctuation..
52.	Optimization of negative ion sources for a heavy-ion-beam probe The development of plasma-sputter-type negative ion sources is underway for the heavy-ion-beam probe system as plasma diagnostic beams of the large helical device (LHD) for potential and fluctuation field measurements. Our purpose is to increase the doubly charged exchanged Au+ beam intensity to enhance the detection signal after passing through the plasmas of the LHD. For this purpose, the characterization of the Au- ion source and the beam optics has been carried out both experimentally and numerically. Based on these results, a new plasma-sputter-type negative ion source is designed and tested. © 2006 American Institute of Physics..
53.	K Kamiya, H Kawashima, T Ido, N Oyama, M Bakhtiari, S Kasai, Y Kusama, Y Miura, H Ogawa, K Tsuzuki, K Uehara, Reduced divertor heat loads, plasma shape effects, and radial electric field structures in JFT-2M HRS H-mode plasmas, NUCLEAR FUSION, 10.1088/0029-5515/46/2/010, 46, 2, 272-276, 2006.02, A key feature of the 'high recycling steady' (HRS) H-mode regimes is the reduction of the transient heat load to the divertor target due to large ELMS. The heat flux to the divertor targets measured by means of a Langmuir probe in the scrape-off layer on the target plate is about similar to 0.3 MW m(-2) in the typical HRS plasmas, which is very small in comparison with the transient heat load in the ELMy H-mode discharge. In addition, the effects of the plasma shaping on the access to and improved plasma performance of HRS H-mode regimes have been investigated. Furthermore, simultaneous measurements of both density fluctuations and potential profiles at the plasma edge region using a heavy ion beam probe are also presented..
54.	K Ida, Y Miura, T Ido, Y Nagashima, K Shinohara, Studies of radial electric field formation and its effect on fluctuations and transport barriers in the JFT-2M tokamak, FUSION SCIENCE AND TECHNOLOGY, 49, 2, 122-138, 2006.02, The mechanism of E x B flow formation, the effect of the E X B flow on parallel flow, the reduction of fluctuations by the shearing effect of the E x B flow shear, and the relation between the geodesic acoustic mode (GAM) and density fluctuations are discussed based on the experiments using various Er measurements in the JFT-2M tokamak. The experiments in plasmas with H-mode and counter-neutral beam injection (NBI) mode show that the feedback loop of the E x B flow shear, the fluctuation suppression, and an increase of ion diamagnetic flow are key to the formation of the transport barrier in toroidal plasmas. Two important effects of the radial electric field are presented: One is fluctuation suppression by the E x B flow shear, and the other is a drive of the parallel flow by radial electric field, which explains the driving mechanism of a spontaneous toroidal flow. The relation between the GAM and the density fluctuations is also discussed. The GAM is observed to be excited by the nonlinear coupling of density fluctuations, while the GAM itself affects the amplitude of the density fluctuations..
55.	Y Nagashima, K Hoshino, A Ejiri, K Shinohara, Y Takase, K Tsuzuki, K Uehara, H Kawashima, H Ogawa, T Ido, Y Kusama, Y Miura, Observation of nonlinear coupling between small-poloidal wave-number potential fluctuations and turbulent potential fluctuations in ohmically heated plasmas in the JFT-2M tokamak, PHYSICAL REVIEW LETTERS, 95, 9, 2005.08, Two types of electrostatic modes with small-poloidal wave numbers (similar to 1 and 10-15 kHz) are observed in the edge region of Ohmically heated plasmas in the JFT-2M tokamak. The envelope of the higher frequency coherent mode is modulated at the frequency of the lower frequency mode. A bispectral analysis revealed that a significant nonlinear coupling among the two types of fluctuations and the broadband background turbulent potential fluctuations occurs inside the last closed magnetic flux surface, suggesting that a nonlinear process such as the parametric-modulational instability is involved..
56.	Y Hamada, A Nishizawa, T Ido, T Watari, M Kojima, Y Kawasumi, K Narihara, K Toi, Zonal flows in the geodesic acoustic mode frequency range in the JIPP T-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/45/2/002, 45, 2, 81-88, 2005.02, Large potential oscillations were detected in JIPPT-IIU tokamak plasmas in a wide range of plasma cross-sections in measurements using a multi-sample-volume heavy ion beam probe. These oscillations have large amplitudes reaching a few hundreds of volts and their frequencies are in the range of the geodesic acoustic mode (GAM). They are found over a wide range of plasma cross-sections and commonly have m = 0 structures. As they were Fourier analysed, it was found that the central frequency is higher in the core of the plasma and lower in the edge of the plasma. These observations agree with the properties of theoretically predicted GAM oscillations. It was also found that the frequency spectrum is peaked in the core and broad in the edge, which may have something to do with damping mechanisms of the GAM. The phase relation between the density and the electric field fluctuations was studied extensively in terms of the cross-correlation function. The level of the density fluctuation was low as it should be,, and the expected 90 degrees phase difference was found in a limited radial domain..
57.	K Kamiya, Y Miura, T Ido, Y Hamada, Calibration of heavy ion beam probe energy analyzer using mesh probe in the JFT-2M tokamak, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.1599057, 74, 9, 4206-4208, 2003.09, A direct calibration technique for a heavy ion beam probe (HIBP) parallel plate electrostatic energy analyzer using the mesh probe is established. When an ac bias voltage (+/-1.0 kV, 50 Hz) is applied to the inner mesh box and He gas is puffed into the vacuum vessel after setting the sample volume within the inner mesh box, it is confirmed that the normalized difference (ND) depends linearly on the applied bias voltage. The slope of the ND with respect to the bias voltage, d(ND)/d(Phi(bias)), shows the clear dependence on the in-plane entrance angle to the analyzer slit that is expected from the ideal analyzer model. Although the mesh transparency of the beam is about 40%, good signal to noise ratio is obtained with a beam current of about 10 muA, and the uncertainty for an absolute calibration of the energy analyzer is less than 10%. Calibration results are in good agreement with previous results using a standard gas target method. (C) 2003 American Institute of Physics..
58.	T Ido, K Kamiya, Y Miura, Y Hamada, A Nishizawa, Y Kawasumi, Observation of the fast potential change at L-H transition by a heavy-ion-beam probe on JFT-2M, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.88.055006, 88, 5, 2002.02, [URL], The fast potential change near the separatrix is measured directly at the L-H transition by a heavy-ion-beam probe. The potential changes with two different time scales at the L-H transition triggered by a sawtooth crash: it drops at first with the time scale of 10-100 mus just after the arrival of the heat pulse due to the sawtooth crash. Then, it decreases again at a few 100 mus after the first drop at a time scale of about 200 mus..
59.	Y Miura, T Ido, K Kamiya, Y Hamada, Relations among potential change, fluctuation change and transport barrier in the JFT-2M tokamak, NUCLEAR FUSION, 10.1088/0029-5515/41/8/301, 41, 8, 973-979, 2001.08, Potential and density/temperature fluctuations at the L-H transition axe measured by the heavy ion beam probe on JFT-2M. It has been observed that the timescale of the potential change is as fast as 10-100 mus when the input power (P(in)) is larger than the L-H threshold power (P(th)). When P(in) similar to P(th), the confinement is improved gradually step by step with sawtooth crashes, After a few sawtooth crashes, the potential drops rapidly to the level of the ELM free H mode. From the gradual change of the potential, assuming that dE(r)/dr is a key to forming and sustaining the transport barrier, the criterion of dE(r)/dr is less than (1.2+/-0.4) x 10(3) kV/m(2). At an ELM just before the H-L transition the potential inside the separatrix also shows a rapid positive jump. The timescales of the positive jump and of thc recovery of the potential to its negative value are about 40 and 150 mus, respectively. Before the H L transition, the time between ELMs and/or dithering transition becomes shorter and the plasma finally goes back to the L mode..
60.	K Kamiya, Y Miura, K Tsuzuki, T Ido, Y Hamada, T Nakayama, Development of mesh probe for the calibration of the HIBP diagnostic system in the JFT-2M tokamak, REVIEW OF SCIENTIFIC INSTRUMENTS, 72, 1, 579-582, 2001.01, A direct calibration technique for the heavy ion beam probe system using the mesh probe is established. The mesh probe makes it possible to calibrate the diagnostic system with the same condition as a real plasma measurement. The location of the sample volume could be determined with the spatial resolution of about 7.5 mm. It shows good agreement with this expected result by the trajectory code with an accuracy of about 1%. (C) 2001 American Institute of Physics..
61.	T Ido, K Kamiya, Y Miura, Y Hamada, A Nishizawa, Y Kawasumi, Temporal behaviour of the potential and fluctuations at the L-H transition on JFT-2M, PLASMA PHYSICS AND CONTROLLED FUSION, 42, A309-A315, 2000.05, Potential and density/temperature fluctuations at the L-H transition are measured by a heavy ion beam probe (HIBP) on JFT-2M. It has been observed that the time scale of potential change is as fast as 10-100 mu s when the input power (P-in) is larger than the L-H threshold power (P-th). When P-in = P-th, the confinement is improved step by step, with sawteeth crashes accompanied by a decrease of potential. After a few sawteeth crashes, the potential drops rapidly to the level of the ELM-free H-mode. At that time, the density/temperature fluctuations are suppressed simultaneously. The observations of the temporal behaviour of the potential and fluctuations in such all L-H transition are reported..
62.	T Ido, K Kamiya, Y Hamada, A Nishizawa, Y Kawasumi, Y Miura, Behaviour of sample volumes of the heavy ion beam probe on JFT-2M, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/41/8/307, 41, 8, 1013-1024, 1999.08, Complex behaviour of sample volumes in heavy ion beam probe (HIBP) is numerically and experimentally explored. Three types of the sample volume divergences are established experimentally. It is found that the comparison of the results of experiments and trajectory calculation can provide calibrations of the HIBP..
63.	T Ido, Y Hamada, A Nishizawa, Y Kawasumi, Y Miura, K Kamiya, Heavy ion beam probe diagnostic system on JFT-2M, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.1149474, 70, 1, 955-958, 1999.01, Heavy ion beam probe (HIBP) on JFT-2M has been installed. The diagnostic system is described briefly alone with a detailed description of planned calibration experiments. Two sets of poloidal and toroidal sweepers are used, one set at the entrance port and the other set at the exit port. These are used to measure a potential profile from the edge to the core of the plasma and to reduce the error due to the change of the angle to the energy analyzer. The calibration of the required voltages on electrodes of these sweepers for the potential profile measurement will be performed by the ionization of the injected beams with the neutral gas puffed into the tokamak chamber, with special emphasis on the effects of peculiar behaviors of the double sample volumes and sample volume divergence. It is found that in JFT-2M HIBP these phenomena do not disturb the calibration of the potential measurement. These peculiar behaviors will be useful for accurately determining the location of the observation point. (C) 1999 American Institute of Physics. [S0034-6748(99)75501-2]..

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