Nonlinear saturation of reverse shear Alfven eigenmodes induced by kinetic electrons

A strong nonlinear saturation mechanism of the reverse shear Alfven eigenmode (RSAE)induced by thermal electrons is observed in gyrokinetic delta f particle-in-cell simulation. This nonlinear effect occurs at moderate mode amplitude, delta B-perpendicular to/B < 10(-3), and is associated with the electron parallel streaming along the perturbed magnetic field lines, the term v(parallel to)delta B-perpendicular to//B center dot del delta f, in the electron drift-kinetic equation. In the case of an n=4 RSAE, where n is the toroidal modenumber, this magnetic fluttering nonlinearity leads to strong mode coupling and broadening of the saturation spectrum. The nonlinear components, which are highly damped through the interaction between thermal electrons and the parallel electric field, modifies the RSAE mode structure and suppresses energetic particle drive significantly. The split-weight scheme (Chen and Parker 2007 J. Comput. Phys.220 839-55) is used to simulate kinetic electrons.