Scalings of energetic particle transport by ion temperature gradient microturbulence

Abstract

Transport scaling of energetic particles by ion temperature gradient microturbulence in magnetized plasmas is studied in massively paralleled gyrokinetic particle-in-cell simulations. It is found that the diffusivity decreases drastically at high particles energy (E) to plasma temperature (T) ratio because of the averaging effects of the large gyroradius and drift-orbit width, and the fast wave-particle decorrelation. At high energy, the diffusivity follows a (E/T)−1 scaling for purely passing particles, a (E/T)−2 scaling for deeply trapped particles and a (E/T)−1 scaling for particles with an isotropic velocity distribution since the diffusivity therein is contributed mostly by the passing particles.