Electron temperature anisotropy instabilities: Computer simulations

An electron temperature anisotropy T-perpendicular to e/T-parallel to 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 \Omega(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 omega(e) similar to \Omega(e)\, where omega(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 beta-dependent upper bound on the electron temperature anisotropy at beta(parallel to e) less than or equal to 0.10 The simulations also demonstrate that the maximum value of the dimensionless fluctuating magnetic fields increases with PII, and that at sufficiently low beta the electrostatic instability leads to non-Maxwellian suprathermal enhancements on the reduced electron velocity distribution f(e)(nu(parallel to)).