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Description
Energetic particle driven instabilities and redistribution in phase space in a tokamak burning plasma with reversed magnetic shear are investigated with kinetic-magnetohydrodynamics (MHD) hybrid simulations. The initial equilibrium is based on an ITER steady-state scenario with 9 MA plasma current and was studied for energetic particle driven instabilities in a previous work [1]. In addition to the conventional hybrid simulation performed in the previous work where alpha particles and beam deuterium ions were simulated with computational particles, an extended hybrid simulation [2] are performed where thermal deuterium and tritium ions are also simulated with computational particles. In the conventional hybrid simulation, many toroidal Alfvén eigenmodes (TAEs) with toroidal mode number n∼15 are the most unstable in the linearly growing phase and low-n Alfvén eigenmodes (AEs) with n~3 become dominant in the nonlinear phase. This is consistent with the previous work. On the other hand, in the extended hybrid simulation with kinetic thermal deuterium and tritium ions, the growth rate and saturation level of TAEs are significantly reduced and the low-n AEs are stabilized. This stabilization can be attributed to Landau damping of kinetic thermal ions. Another Alfvénic instability with n=25 is found driven by kinetic thermal ions in the extended hybrid simulation. The spatial profile of radial MHD velocity is dominated by a single poloidal component m=39 while the radial magnetic perturbation is dominated by two poloidal components m=38 and 40. The distribution function analysis of alpha particles and beam deuterium ions in the conventional hybrid simulation indicates that the excitation of many TAEs results in the formation of a transient stairway structure in phase space leading to the global flattening caused by resonance overlap. The nonlinear evolution of the distribution function of alpha particles and beam deuterium ions interacting with the low-n AEs is discussed.
[1] Y. Todo and A. Bierwage, Plasma Fusion Res. 9, 3403068 (2014).
[2] Y. Todo et al., Plasma Phys. Control. Fusion 63, 075018 (2021).
| Presentation type | Oral |
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