Core localized alpha-channeling via low frequency Alfven mode generation in reversed shear scenarios

Abstract

A novel channel for fuel ions heating in tokamak core plasma is proposed and analyzed using nonlinear gyrokinetic theory. The channel is achieved via spontaneous decay of reversed shear Alfvén eigenmode (RSAE) into low frequency Alfvén modes (LFAM), which then heat fuel ions via collisionless ion Landau damping. The conditions for RSAE spontaneous decay are investigated, and the saturation level and the consequent fuel ion heating rate are also derived. The channel is expected to be crucial for future reactors operating under reversed shear configurations, where fusion alpha particles are generated in the tokamak core where the magnetic shear is typically reversed, and there is a dense RSAE spectrum due to the small alpha particle characteristic dimensionless orbits.

Perturbative analysis of low-frequency instabilities in high-field ST40 experiments

“…We note, however, that the validity of an ideal MHD description for modes with low frequency (as compared to the Alfvén frequency) is in general limited. Those modes are known to be damped at high T i /T e [35] and can also be damped due to the inclusion of effects not present in NOVA analysis, such as thermal ion damping in a (gyro)kinetic framework, parallel electric fields and nonperturbative and diamagnetic effects [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] 6 .…”