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Idomura, Yasuhiro
Physics of Plasmas, 26(12), p.120703_1 - 120703_5, 2019/12
Times Cited Count：5 Percentile：33.23(Physics, Fluids & Plasmas)This Letter presents the impacts of the hydrogen isotope mass and the normalized gyroradius 
on L-mode like hydrogen (H) and deuterium (D) plasmas dominated by ion temperature gradient driven (ITG) turbulence using global full-f gyrokinetic simulations. In ion heated numerical experiments with adiabatic electrons, the energy confinement time shows almost no isotope mass dependency, and is determined by Bohm like scaling. Electron heated numerical experiments with kinetic electrons show clear isotope mass dependency caused by the isotope effect on the collisional energy transfer from electrons to ions, and the H and D plasmas show similar ion and electron temperature profiles at an H to D heating power ratio of 
. The normalized collisionless ion gyrokinetic equations for H and D plasmas become identical at the same , and collisions weakly affect ITG turbulence. Therefore, the isotope mass dependency is mainly contributed by the scaling and the heating sources.
Idomura, Yasuhiro
Physics of Plasmas, 24(8), p.080701_1 - 080701_5, 2017/08
Times Cited Count：10 Percentile：45.63(Physics, Fluids & Plasmas)An electron heating modulation numerical experiment based on a global full-f gyrokinetic model shows that transitions from ion temperature gradient driven (ITG) turbulence to trapped electron mode (TEM) turbulence induced by electron heating generate density peaking and rotation changes. Toroidal angular momentum balance during the rotation changes is revealed by direct observation of toroidal angular momentum conservation, in which in addition to ion turbulent stress, ion neoclassical stress, radial currents, and toroidal field stress of ions and electrons are important. Toroidal torque flipping between ITG and TEM phases is found to be related to reversal of the ion radial current that indicates coupling of particle and momentum transport channels. The ion and electron radial currents are balanced to satisfy the ambipolar condition, and the electron radial current is cancelled by the electron toroidal field stress, which indirectly affects toroidal torque.
Maeyama, Shinya*; Idomura, Yasuhiro; Watanabe, Tomohiko*; Nakata, Motoki*; Yagi, Masatoshi; Miyato, Naoaki; Ishizawa, Akihiro*; Nunami, Masanori*
Physical Review Letters, 114(25), p.255002_1 - 255002_5, 2015/06
Times Cited Count：92 Percentile：95.19(Physics, Multidisciplinary)Multiscale gyrokinetic turbulence simulations with the real ion-to-electron mass ratio and 
value are realized for the first time, where the value is given by the ratio of plasma pressure to magnetic pressure and characterizes electromagnetic effects on microinstabilities. Numerical analysis at both the electron scale and the ion scale is used to reveal the mechanism of their cross-scale interactions. Even with the real- mass scale separation, ion-scale turbulence eliminates electron-scale streamers and dominates heat transport, not only of ions but also of electrons. When the ion-scale modes are stabilized by finite- effects, the contribution of the electron-scale dynamics to the turbulent transport becomes non-negligible and turns out to enhance ion-scale turbulent transport.
Kishimoto, Yasuaki
Purazuma, Kaku Yugo Gakkai-Shi, 80(5), p.390 - 395, 2004/05
High performance magnetically confined plasma is realized by having structures in plasmas, where different elementary processes with different time and spatial scales are deeply contributing with each other. A research based on large scale simulation is then essential to understand such hierarchical complex plasmas. We discuss the underlying physical process of the structural plasma and present a prospect for future numerical simulations covering a wide dynamical range.
Bruskin, L. G.; Mase, Atsushi*; Oyama, Naoyuki; Shinohara, Koji; Miura, Yukitoshi
Plasma Physics and Controlled Fusion, 45(7), p.1227 - 1245, 2003/07
Times Cited Count：7 Percentile：22.85(Physics, Fluids & Plasmas)The capability of microwave reflectometry to estimate the nonlinear coupling in the plasma turbulence is theoretically investigated. The full-wave 2D model of microwave scattering in plasma is applied to simulate the reflectometer response to the turbulent fluctuations, consisting of random and coherent modes, and the simulated data ensemble is further processed to obtain the auto bicoherence function. Sensitivity of the method was analyzed for different ambient plasma profiles, geometry, fluctuation spectra and amplitudes.
Progress of Theoretical Physics, 38(3), p.576 - 583, 1967/00
Times Cited Count：3no abstracts in English
Kawai, Chika; Maeyama, Shinya; Idomura, Yasuhiro; Ogawa, Yuichi*
no journal, ,
Self-organization through inverse cascades of energy in a turbulent spectrum is considered as one of the paths to formation of zonal flow structures in magnetized plasma. Despite the theoretical suggestion, relations between the turbulence energy spectrum and the formation of zonal flow structures have not been rigorously investigated in terms of numerical simulation studies based on a first-principle model. In this study, spectrum structures of electron scale plasma turbulence are obtained from high-resolution Vlasov simulations. The long wave length region of the spectrum is investigated in relation with self-organization.
Kawai, Chika; Idomura, Yasuhiro; Maeyama, Shinya; Ogawa, Yuichi*
no journal, ,
In estimating confinement properties of fusion plasmas, it is a critical issue to understand structures of turbulent spectra, leading to turbulent transport. In this study, self-organization processes, which produce zonal flows from electron turbulence, are analyzed in detail via a highly accurate gyrokinetic Eulerian code, and structures of turbulent spectra leading to zonal flow generation are clarified.
Idomura, Yasuhiro
no journal, ,
To study fusion plasma turbulence, the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D has been developed. On the K-computer, inter-node parallelization techniques such as multi-dimensional/-layer domain decomposition and communication-computation overlap were developed, and strong scaling of GT5D was improved up to 73,728 nodes. However, extensions of GT5D towards burning plasmas including kinetic electrons and multi-species ions require greater computing power. Under the post-K project, we have developed computing techniques for the next generation platforms such as GPUs and MICs. In this talk, we discuss computational challenges related to complicated intra-node memory hierarchy on many core processors and relatively limited inter-node communication performance compared with accelerated computation.
Idomura, Yasuhiro
no journal, ,
Fusion plasma turbulence often shows self-organized turbulent structures such as zonal flows. This phenomenon has been is discussed by analogy with a self-organization picture described by the Hasegawa-Mima (H-M) equation. Although the H-M equation predicts several important features such as the dual cascade of turbulent spectra, the Rhines scale, and the adiabatic response scale, these basic features have not examined in fusion plasma turbulence so far. In this talk, we present the self-organization of electron temperature gradient driven turbulence, examine these basic features, and discuss their impact on turbulent transport.
Asahi, Yuichi; Fujii, Keisuke*; Maeyama, Shinya*; Idomura, Yasuhiro
no journal, ,
We propose to use a dimensionality reduction technique, namely principal component analysis (PCA) to extract patterns from the series of 5D gyrokinetic plasma simulation data. It is shown that 83% of the variance of the original 6D (5D phase space + 1D time) data can be expressed with 64 principal components. Through the detailed analysis of the contribution of each principal component to the energy flux, we demonstrate that the avalanche like energy transport is driven by coherent mode structures in the phase space, indicating the key role of resonant particles.
