Convective transport of fast particles in dissipative plasmas near an instability threshold

Abstract

We demonstrate that a marginally unstable energetic particle population in a dissipative plasma can change globally due to the act of a single wave–particle resonance. The resonance serves as a seed for the continuous production of nonlinear holes and clumps, whose convective motion in phase-space results in substantial flattening of the fast particle distribution function. The holes and clumps can emerge recurrently without any particle source or collisional relaxation process that would restore the particle distribution function at the resonance. A bump-on-tail instability is considered as an example in a single-mode limit as well as in the quasilinear regime. The convective hole-clump transport tends to be more significant near the instability threshold than quasilinear diffusion.