Dissipation of Kinetic Alfvénic Turbulence as a Function of Ion and Electron Temperature Ratios

Abstract

Two-and-one-half dimensional particle-in-cell simulations of the forward cascade and dissipation of decaying kinetic Alfvenic turbulence have been carried out on a model of a collisionless, homogeneous, magnetized ion-electron plasma. The uniform background magnetic field B-o lies parallel to the simulation plane. The simulations were executed as part of the Turbulent Dissipation Challenge. Initial narrowband magnetic fluctuation spectra of kinetic range Alfven waves undergo a forward cascade to broadband turbulent spectra at shorter wavelengths, at the same time undergoing dissipative transfer of fluctuating field energy to kinetic energy of electrons and ions. The simulations yield Q(i) and Q(e), the dimensionless rates of kinetic energy density gain for ions (subscript i) and electrons (subscript e). These are computed for five different initial values of beta(i)/beta(e). For the parameters chosen here, the simulations yield the scaling relation Q(e)/Q(i) approximate to 2(T-i/T-e)(2) where T-j represents the initial temperature of the jth species. For all simulation times the kinetic anisotropy of the ions changes monotonically in the sense of greater energy passing from the fluctuations into ion velocities parallel to, rather than perpendicular to, B-o, suggesting that Landau damping is an important ion dissipation mechanism for kinetic Alfvenic turbulence.