Theory and simulation of the whistler instability driven by a velocity space anisotropy

A one-dimensional fully electromagnetic finite-size particle simulation code is used to study instabilities driven by an anisotropic electron velocity distribution. Wave propagation is restricted parallel to an external magnetic field. The unstable frequency spectrum is found to be dominated by the whistler mode. Whereas some modes in the unstable spectrum grow and damp according to linear theory, the saturation of the average fluctuation could be due to particle trapping effects. The 1 = 2 mode is found to grow during the non-linear (post-saturation) stage of the instability. It is conjectured that the physical mechanism responsible for its growth is a wave-wave-particle interaction