Whistler anisotropy instability: Spectral transfer in a three‐dimensional particle‐in‐cell simulation

Abstract

A three‐dimensional (3‐D) particle‐in‐cell (PIC) simulation of the whistler anisotropy instability is carried out for a collisionless, homogeneous, magnetized plasma with βe=0.10. This is the first 3‐D PIC simulation of the evolution of enchanced fluctuations from this growing mode driven by an anisotropic electron velocity distribution with T⟂e/T∥e>1 where ⟂ and ∥ represent directions perpendicular and parallel to the background magnetic field Bo, respectively. The early‐time magnetic fluctuation spectrum grows with properties reflecting the predictions of linear theory with narrowband maxima at kc/ωe≃ 1 and k×Bo=0, and a wave vector anisotropy in the sense of k⟂<<k∥. Here ωe represents the electron plasma frequency. At later times the fluctuations undergo both a forward transfer to shorter wavelengths, also with k⟂<<k∥, and an inverse transfer to longer wavelengths with wave vector anisotropy k⟂>>k∥. The inverse transfer is consistent with a prediction of nonlinear three‐wave coupling theory.