| Co-Investigator(Kenkyū-buntansha) |
SATAKE Shinsuke National Institute for Fusion Science, Theory and Computer Simulation Center, Research Fellow of JSPS, 理論シミュレーション研究センター, 日本学術振興会特別研究員・PD
WATANABE Tomohiko National Institute for Fusion Science, Theory and Computer Simulation Center, Associate Professor, 理論シミュレーション研究センター, 助教授 (30260053)
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| Research Abstract |
Neoclassical Transport Theory : Lagrangian formulation of transport theory, which has been investigated to reflect finiteness of guiding-center orbit widths to transport equations, is developed in order to analyze neoclassical transport near the axis for a low-collisionality plasma. By directly reflecting the orbital properties of all the types of orbits in calculation, the ion thermal conductivity around the axis is found to decrease from that predicted by conventional neoclassical theory.
A novel method to obtain the full neoclassical transport matrix for general toroidal plasmas, by using the solution of the linearized drift kinetic equation with the pitch-angle-scattering collision operator is shown. In this method, the neoclassical coefficients for both poloidal and toroidal viscosities in toroidal helical systems can be obtained, and the neoclassical transport coefficients for the radial particle and heat fluxes and the bootstrap current with the nondiagonal coupling between unlik
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e-species particles are derived from combining the viscosity-flow relations, the friction-flow relations, and the parallel momentum balance equations.
Turbulent Transport Theory : A novel nondissipative closure model (NCM) is presented to give a set of fluid equations which describe a collisionless kinetic system. In order to take account of the time reversal symmetry of the collisionless kinetic equation, the new closure model relates the parallel heat flux to the temperature and the parallel flow in terms of the real-valued coefficients in the unstable wave number space. When the NCM is applied to the three-mode ion temperature gradient (ITG) driven system, the fluid system of equations reproduces the exact nonlinear kinetic solution.
A detailed comparison between kinetic and fluid simulations of collisionless slab ITG driven turbulence is made. Simulation results show that, in the saturated turbulent state, the turbulent thermal diffusivity obtained from the kinetic simulation is well reproduced by the fluid simulation using the NCM.
Electromagnetic microinstabilities in helical systems are studied by numerically solving integral eigenmode equations, which are derived from the ion gyrokinetic equation, the quasineutrality equation, the Ampere's law, and the massless electron approximation. For helical geometry like the Large Helical Device (LHD), it is confirmed that, when increasing the beta value, the ITG mode is stabilized while the kinetic ballooning mode (KBM) is destabilized due to the unfavorable geodesic curvature resulting from the negative magnetic shear combined with the toroidal plasma shift. Less
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