Whistler anisotropy instability: Wave‐particle scattering rate

Abstract

An electron temperature anisotropy T ⊥ e > T ∥ e (where ⊥ and ∥ refer to directions relative to the background magnetic field) can excite the whistler anisotropy instability in a collisionless plasma. The resulting enhanced fluctuating magnetic fields scatter the electrons and reduce the anisotropy. We use particle‐in‐cell simulations in a spatially homogeneous plasma model to compute the maximum values of the wave‐particle scattering rate for electron anisotropy reduction. This rate scales as the electron cyclotron frequency but, for a fixed initial growth rate, is relatively independent of the electron temperature if k B T e ≤ 5 keV. For larger electron temperatures, the scattering rate decreases with increasing T e , suggesting that relativistic effects play a role.