Nonlinear inverse Landau damping of ion Bernstein waves on alpha particles

Abstract

A novel scheme to realize the alpha-channeling concept in tokamak plasmas is proposed. It is based on (i) the free energy available due to the inversion of the population of alpha particles in velocity space and (ii) the nonlinear inverse Landau damping of ion Bernstein waves (IBW). The latter occurs at Doppler shifted half-integer harmonics of the ion-cyclotron resonance Based on single-particle, single-wave analysis, we derive the diffusion tensors in the phase space associated to the nonlinear IBW- interaction. Numerical solutions of a Fokker–Planck equation, including the collisional operator as well as the source and sink terms show that alpha power can be channeled into IBW power during the time evolution of the alpha particle distribution function towards a steady state. For sufficient large loss rate compared to the slowing down rate, inversion of population in velocity space and alpha channeling can occur also at the steady state.