Gyrokinetic particle simulation of nonlinear evolution of mirror instability

A gyrokinetic simulation model for nonlinear studies of the mirror instability is described. The model is set in a uniform, periodic slab with anisotropic ions and cold electrons. Particle-in-cell simulations with a noise reducing falgorithm show agreement with the linear theory of the mirror instability. Results of nonlinear simulations near marginal stability are presented. Single-mode simulations show saturation due to trapping. Simulations with a spectrum of unstable modes show that the negative magnetic perturbations saturate at a lower amplitude and earlier than the positive magnetic perturbations, which results in the development of peaked saturated structures. The saturation amplitude of negative magnetic perturbations is in agreement with the trapped particle theory, while the saturation amplitude of the positive magnetic perturbations is determined by the local change in the (ratio of perpendicular plasma pressure to magnetic pressure) parameter.