Numerical simulations of collisionless drift instabilities for low-density plasmas

Nonlinear behavior of the collisionless drift instabilities are studied for the universal and current driven modes by means of electrostatic particle simulations in two-and-a-half dimensions. Realistic mass ratios of electrons to the ions are used in the simulations, where the guiding-center approximation for the electrons and the exact dynamics for the ions are employed. Several nonlinear effects including the quasi-linear diffusion of the particle density, the frequency shift due to the ambipolar field, the mode competition among the unstable waves, and the quasi-linear diffusion in the velocity space are found to be dominant mechanisms for the saturation. The stabilization of the collisionless drift instabilities by the magnetic shear has also been studied.