Multi-phase hybrid simulation of energetic particle driven magnetohydrodynamic instabilities in tokamak plasmas

Abstract

Magnetohydrodynamic (MHD) instabilities driven by energetic particles in tokamak plasmas and the energetic particle distribution formed with the instabilities, neutral beam injection, and collisions are investigated with hybrid simulations for energetic particles and anMHDfluid. The multi-phase simulation, which is a combination of classical simulation and hybrid simulation, is applied to examine the distribution formation process in the collisional slowing-down time scale of energetic ions for various beam deposition power (PNBI) and slowing-down time (ts). The physical parameters other than PNBI and ts are similar to those of a Tokamak Fusion Test Reactor (TFTR) experiment (Wong et al 1991 Phys. Rev. Lett. 66 1874). For PNBI =10MWand ts =100 ms, which is similar to the TFTR experiment, the bursts of toroidal Alfven eigenmodes take place with a time interval 2 ms, which is close to that observed in the experiment. The maximum radial velocity amplitude (vr) of the dominant TAE at the bursts in the simulation is vr/ vA ∼ 3 × 10-3 where vA is the Alfven velocity at the plasma center. For PNBI =5MWand ts =20 ms, the amplitude of the dominant TAE is kept at a constant level vr/ vA∼ 4 × 10-4. The intermittency of TAE rises with increasing PNBI and increasing ts (=decreasing collision frequency). With increasing volume-averaged classical energetic ion pressure,which iswell proportional to PNBI ts, the energetic ion confinement degradesmonotonically due to the transport by the instabilities. The volume-averaged energetic ion pressure depends only on the volume-averaged classical energetic ion pressure, not independently on PNBI or ts. The energetic ion pressure profile resiliency, where the increase in energetic ion pressure profile is saturated, is found for the caseswith the highest PNBIts where the TAE bursts take place.