Electron temperature anisotropy instabilities: Computer simulations

An electron temperature anisotropy T ⊥ e / T ‖ e > 1 leads to excitation of three distinct modes, the whistler, the electrostatic, and the Z‐mode instabilities, in collisionless plasmas at frequencies below the electron cyclotron frequency |Ω e |. (Here perpendicular and parallel subscripts denote directions relative to the background magnetic field.) Two‐and‐one‐half‐dimensional particle‐in‐cell simulations are used to study the nonlinear consequences of the growth of these modes in homogeneous plasmas with ω e ∼ |Ω e |, where ω e is the electron plasma frequency. The simulations show that wave‐particle scattering by enhanced fluctuations from the whistler and electrostatic anisotropy instabilities imposes a β‐dependent upper bound on the electron temperature anisotropy at β ‖ e ≤ 0.10. The simulations also demonstrate that the maximum value of the dimensionless fluctuating magnetic fields increases with β ‖ e and that at sufficiently low β the electrostatic instability leads to non‐Maxwellian suprathermal enhancements on the reduced electron velocity distribution f e ( v ‖ ).