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Tokuda, Makoto*; Mashimo, Tsutomu*; Khandaker, J. I.*; Ogata, Yudai; Mine, Yoji*; Hayami, Shinya*; Yoshiasa, Akira*
Journal of Materials Science, 51(17), p.7899 - 7906, 2016/09
Times Cited Count：2 Percentile：7.58(Materials Science, Multidisciplinary)Januszko, K.*; Stabrawa, A.*; Ogata, Yudai; Tokuda, Makoto*; Khandaker, J. I.*; Wojciechowski, K.*; Mashimo, Tsutomu*
Journal of Electronic Materials, 45(3), p.1947 - 1955, 2016/03
Times Cited Count：5 Percentile：31.21(Engineering, Electrical & Electronic)Ogata, Yudai*; Iguchi, Yusuke*; Tokuda, Makoto*; Januszko, K.*; Khandaker, J. I.*; Ono, Masao; Mashimo, Tsutomu*
Journal of Applied Physics, 117(12), p.125902_1 - 125902_6, 2015/03
Times Cited Count：8 Percentile：34.64(Physics, Applied)Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Oyama, Naoyuki; Kojima, Atsushi; Tokuda, Shinji*; Yagi, Masatoshi
Nuclear Fusion, 51(7), p.073012_1 - 073012_9, 2011/07
We investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode. Based on these results, we investigate numerically the stability of JT-60U type-I ELMy H-mode plasmas, and show that the toroidal rotation plays an important role for making the difference of ELM behavior observed in JT-60U plasmas with different plasma rotation profiles.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Oyama, Naoyuki; Kojima, Atsushi; Tokuda, Shinji*; Yagi, Masatoshi
Nuclear Fusion, 51(7), p.073012_1 - 073012_9, 2011/07
Times Cited Count：21 Percentile：65.79(Physics, Fluids & Plasmas)Mechanisms of plasma rotation on edge MHD stability is investigated numerically by introducing energies that are distinguished by physics. By comparing them, it is found that an edge localized MHD mode is destabilized by the difference between an eigenmode frequency and an equilibrium toroidal rotation frequency, which is induced by rotation shear. In addition, this destabilizing effect becomes effective in the shorter wavelength region. The effect of poloidal rotation on the edge MHD stability is also investigated. Under the assumption that the change of an equilibrium by poloidal rotation is negligible, it is identified numerically that poloidal rotation can have both the stabilizing effect and the destabilizing effect on the edge MHD stability, which depends on the direction of poloidal rotation. Numerical analysis demonstrates that these effects of plasma rotation in both toroidal and poloidal directions can play important roles on type-I ELM phenomena in JT-60U H-mode plasmas.
Hirota, Makoto; Tokuda, Shinji*
Physics of Plasmas, 17(8), p.082109_1 - 082109_11, 2010/08
Times Cited Count：8 Percentile：30.82(Physics, Fluids & Plasmas)Invariance of wave action for eigenmodes and continuum modes around quasi-stationary equilibrium state is investigated in a general framework that allows for the ideal magnetohydrodynamic system and the Vlasov-Maxwell system. By utilizing the averaging method for the variational principle, the wave action of each mode is shown to be conserved if its frequency (spectrum) is sufficiently separated from other ones, whereas some conservative exchange of the wave action may occur among the modes with close frequencies. This general conservation law is, as an example, demonstrated for a situation where the Landau damping (or growth) occurs due to a resonance between an eigenmode and a continuum mode. The damping (or growth) rate is closely related to the spectral linewidth (= the phase mixing rate) of the continuum mode, which can be estimated by the invariance of wave action without invoking the conventional analytic continuation of the dispersion relation.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji
Nuclear Fusion, 50(4), p.045002_1 - 045002_13, 2010/04
Times Cited Count：22 Percentile：64.1(Physics, Fluids & Plasmas)In this paper, we investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.
Kamada, Yutaka; Yoshino, Ryuji; Ushigusa, Kenkichi; Neyatani, Yuzuru; Oikawa, Toshihiro; Naito, Osamu; Tokuda, Shinji; Shirai, Hiroshi; Takizuka, Tomonori; Ozeki, Takahisa; et al.
Fusion Energy 1996, Vol.1, p.247 - 258, 1997/00
no abstracts in English
Hirota, Makoto; Tokuda, Shinji; Fukumoto, Yasuhide*
no journal, ,
Hirota, Makoto; Tokuda, Shinji
no journal, ,
Effects of flows on the MHD instabilities have been drawing considerable attention. The standard energy principle, however, is not applicable to flowing plasmas, because waves with negative energy may be stable in such moving media. Additional theoretical framework is needed to study how negative energy modes occur and trigger instabilities, and we discuss it by taking the resistive wall mode as an example. The external kink mode, being stabilized by the wall, assumes negative energy when the Doppler shift due to the flow exceeds a critical value. The energy dissipation at the resistive wall destabilizes this mode. To attain stability condition, another physical mechanism different from dissipation must be taken into account.
Hirota, Makoto; Tokuda, Shinji
no journal, ,
Resonant damping (e.g. continuum damping, Landau damping) of MHD wave is a key issue in various stability problems. In fact, accurate estimation of the damping (or growth) rate is needed for the resistive wall mode and the toroidicity-induced Alfv
n eigenmode. Recently, we have formulated wave action not only for eigenmodes but also for continuum mode, and found that the wave action is conserved among these modes in the process of resonant coupling. This fact can provide another approach to the estimation of resonant damping.
Aiba, Nobuyuki; Tokuda, Shinji; Furukawa, Masaru*; Hirota, Makoto; Oyama, Naoyuki
no journal, ,
Effects of a toroidal rotation are investigated numerically on the stability of the MHD modes in the edge pedestal, which relate to the type-I edge-localized mode (ELM). A new linear MHD stability code MINERVA is developed for solving the Frieman-Rotenberg equation, which is the linear ideal MHD equation with flow. As the result of the stability analysis, it is revealed that the sheared toroidal rotation destabilizes the edge localized MHD modes. The change of the safety factor profile affects this destabilizing effect. This is because the rotation effect on the edge MHD stability becomes stronger as the toroidal mode number of the unstable MHD mode increases, and this toroidal mode number strongly depends on the safety factor profile.
Hirota, Makoto; Tokuda, Shinji
no journal, ,
Resonant damping of an eigenmode, caused by such as the Alfvn resonance and the wave-particle interaction, is an important phenomenon in both fusion and astrophysical plasmas. In this work, the wave actions of eigenmodes and continuum modes are formulated. Their invariance (i.e., the adiabatic invariance) is shown to be useful for the estimation of resonant damping.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji
no journal, ,
no abstracts in English
Hirota, Makoto; Tokuda, Shinji
no journal, ,
In various theories such as stability, wave-mean field interaction and weak turbulence, the wave action (or wave quantum) is worth studying since it is conserved with good accuracy in weakly nonlinear phenomena. In this work, without invoking the short wavelength limit, we have developed a technique for evaluating the wave action not only for each single eigenmode, but also for a continuum mode. The adiabatic invariance of the wave action can be discussed for both eigenmodes and continuum modes. It is decisive in determining whether resonant coupling between an eigenmode and a continuum mode leads to either exponential growth or continuum damping (Landau damping).
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji
no journal, ,
In this paper, we investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.
Hirota, Makoto; Tokuda, Shinji
no journal, ,
Adiabatic invariance of wave action is investigated for generaleigenmodes and continuum modes by exploiting the variational principlefor linearized dynamical systems. Given a sufficiently slow evolution of the background fields, thewave action (or the action variable) attributed to each mode isconserved as long as the corresponding discrete or continuous spectrumis isolated from other spectra and zero frequency. The resonantcoupling allows exchange of wave action among these modes.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji
no journal, ,
In this paper, we investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji*
no journal, ,
We investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji*
no journal, ,
We investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.
Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji*
no journal, ,
We investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.
