Nonlinear evolution of whistler instabilities

Abstract

Theoretical and computer simulation studies of whistler instabilities in anisotropic collisionless plasmas are presented. Initial bi-Maxwellian, Maxwellian with loss cone, and hot Maxwellian superimposed on a more dense cold isotropic background electron distributions were used. Many of the observed features are common to all cases. Initially, the total wave magnetic energy grows; the average growth rate is in good agreement with linear theory; and the electron distribution isotropizes rapidly with a concomitant switching off of high k number, initially unstable waves. Then, the total wave magnetic energy saturates and at this time there is a residual kinetic energy anisotropy. This anisotropy persists after saturation, although there is a further tendency toward isotropy, together with a further switching off of the higher mode numbers for the remainder of the simulation. Throughout the simulation experiments the perpendicular and parallel energy constants are conserved to good accuracy.