Journal Article

Energetic particle driven Alfvén eigenmodes and associated energetic particle redistribution in a tokamak burning plasma

Wang, Jialei, Sato, M, Todo, Y, Li, Hanzheng, Idouakass, M, Seki, R, Wei, Shizhao, Wang, Hao

2025

Overview

Energetic-particle driven Alfvén eigenmodes (AEs) and associated redistribution of energetic particles in phase space are investigated using kinetic-magnetohydrodynamic (MHD) hybrid simulations for a tokamak burning plasma with weakly reversed magnetic shear. The initial MHD equilibrium and plasma profile are those of ITER, which was studied in Todo and Bierwage (2014 Plasma Fusion Res. 9 3403068). Two types of kinetic-MHD hybrid simulations are performed and the results are compared. In the first type of simulation (KEP-MHD simulation), energetic particles are simulated using the gyrokinetic particle method, while in the second type (KEPTI-MHD simulation), both energetic particles and bulk ions are simulated using the gyrokinetic particle method. In the KEP-MHD simulation result, it is observed that multiple toroidal AEs (TAEs) with toroidal mode number n∼15 are the most unstable in the linear growth phase, while reversed shear AEs (RSAEs) with low-n dominate in the nonlinear phase. In the KEPTI-MHD simulation result, it is observed that beta-induced AEs with n∼15 have the largest linear growth rate, while TAEs with n∼10 dominate in the nonlinear phase. The redistribution of energetic particles is substantial and comparable between the two simulations. Redistribution of energetic alpha particles and beam deuterons in phase space is analyzed for the KEP-MHD simulation. In the early nonlinear phase, local flattening regions are formed around the resonances with the AEs. Staircase-like structures are formed along the E′=const. lines for the dominant AEs with amplitudes of radial MHD velocity normalized by the Alfvén velocity vr/vA∼4×10−4, where E′ is the conserved quantity of the wave-particle interaction. As the amplitudes of the AEs increase to vr/vA∼10−3, the resonance regions broaden and overlap each other leading to the formation of a single flattened region. In the KEP-MHD simulation, it is observed that the steep gradient regions in phase space formed by the multiple TAEs excite the low-n RSAE that transports energetic alpha particles near the plasma center. This process extends the flattened region of energetic alpha particle distribution to the plasma center. The stabilizing effect of thermal ions on AEs is demonstrated by analyzing redistribution in phase space for the KEPTI-MHD simulation.

• Publisher: IOP Publishing
• Subject: Alpha particles / Alpha rays / Amplitudes / Deuterons / Energetic particles / Flattening / Magnetohydrodynamics / Nuclear power plants / Particle interactions / Particle methods (mathematics) / Plasma / Simulation / Tokamak devices / Wave-particle interactions