Nonlinear evolution of driven ion acoustic waves in plasmas with super-Gaussian electron velocity distributions: Fluid vs particle-in-cell simulations

Abstract

The nonlinear evolution of driven ion acoustic waves (IAWs) in plasmas with super-Gaussian electron distribution functions (EDFs) is numerically investigated by one-dimensional fluid and particle-in-cell (PIC) simulations. The IAW nonlinearities observed by fluid simulation show significant differences in thermal and nonthermal plasmas. It is noted that for the same fundamental potential amplitude, the harmonic and the nonlinear frequency shift are smaller in plasmas having super-Gaussian distribution as compared to Maxwellian distribution. A frequency mismatch between the driver frequency and the plasma linear response frequency has been introduced in fluid simulations to model the kinetic effect. The occurrence of each type of instability is clarified as a function of the sign and size of the frequency mismatch. The kinetic effect of particle trapping-induced nonlinear frequency shift is calculated for super-Gaussian EDFs. The PIC simulation revealed that trapped electrons can play a contrary role as trapped ions on IAW two-ion decay instabilities, which is consistent with fluid simulations.