Particle-in-cell simulations of whistler waves excited by an electron k distribution in space plasma

摘要

Satellite observations clearly reveal that superthermal electrons in space plasmagenerally possess a pronounced non-Maxwellian distribution that can be well modeled bya tc distribution. In this paper, one-dimensional (1-D) particle-in-cell simulations areperformed to investigate the evolution of whistler waves driven by superthermal electronswith a typical tt distribution in the presence of a cold plasma population. The resultsobtained from the linear theory are first confirmed: with the increase of the spectral index for the ic distribution, the linear growth rate of the excited waves increases andinstability threshold for the temperature anisotropy (A = T_I/T_||—1) decreases. Then wefurther find that with the increase of k, the fluctuating magnetic field energy density at thesaturation stage also increases. Therefore, from both the linear growth rate and thefluctuating magnetic field energy density at the saturation stage, we can find that a bi-Maxwellian distribution (ku) overestimates the importance of whistler waves,since the observed value of k lies in the range 2 Uk 6. We also find that the ic values ofthe electron distributions become smaller with the excitation of the whistler waves.