Particle-in-cell Simulations of Electron and Ion Dissipation by Whistler Turbulence: Variations with Electron β

Abstract

Two ensembles of three-dimensional particle-in-cell (PIC) simulations of the forward cascade of decaying whistler turbulence have been carried out on a model of collisionless, homogeneous, magnetized plasma with parameters similar to those of the solar wind near Earth. Initial, relatively isotropic, narrowband spectra of relatively long wavelength modes cascade to anisotropic, broadband spectra of magnetic fluctuations at shorter wavelengths. Electron and ion dissipation rates are computed as functions of the initial electron beta, β e , over the range 0.1 ≤  β e  ≤ 5.0, where this quantity is varied by changes in the background magnetic field magnitude B o . Ensemble One holds the value of the dimensionless initial magnetic fluctuation energy density ϵ o  ≡ Σ k constant; Ensemble Two follows solar wind observations, imposing the initial condition ϵ o  = 0.20 β e . In both ensembles, the maximum dissipation rate of the electrons, Q e , and the maximum dissipation rate of the ions, Q i , satisfy Q e  ≫  Q i . In Ensemble One, both dissipation rates scale approximately as , whereas over 0.1 ≤  β e  ≤ 1.0 in Ensemble Two, Q e is approximately constant while Q i scales approximately as . These results, when combined with conclusions from earlier PIC simulations, suggest that sufficiently long wavelength and sufficiently large-amplitude magnetosonic-whistler turbulence at sufficiently large β e may heat ions more rapidly than electrons.