Whistler anisotropy instability: Spectral transfer in a threedimensional particleincell simulation

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 backgroundmagnetic field Bo, respectively. The early-timemagnetic 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.