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

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. 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 mechanism tends to be more efficient near the instability threshold than quasilinear diffusion.