HYBRID SIMULATIONS OF THE EFFECTS OF ENERGETIC PARTICLES ON LOW-FREQUENCY MHD WAVES

A hybrid MHD-gyrokinetic simulation model is presented which is suitab le for self-consistent study of the interaction of energetic particles with low-frequency MHD waves. Fully electromagnetic gyrokinetic equat ions are used to describe the energetic particles, while the cold back ground plasma is treated as a fluid, using nonlinear one-fluid MHD equ ations. Based on this model a hybrid MHD-gyrokinetic particle code has been developed. A delta f algorithm has been implemented in the code for beta similar to 1 electromagnetic perturbations. The gyrokinetic d escription enables us to remove the restriction on the particle time s tep dictated by the gyromotion, while the delta f algorithm strongly r educes the simulation numerical noise level. Therefore, considerably l arger time steps and a smaller number of particles can be used in the simulations as compared to conventional methods. The conservation prop erties of the model and corresponding delta f scheme have been investi gated. Representative two-dimensional simulations of the mirror instab ility and the temperature gradient driven instability of the compressi onal mode were performed, and the simulation results are in very good agreement with linear theory. (C) 1997 Academic Press.