Multiscale Nature of the Dissipation Range in Gyrokinetic Simulations of Alfvénic Turbulence

Abstract:

The gyrokinetic turbulence code GENE is used to analyze the dissipation range in kinetic Alfvén wave turbulence. In particular, we focus on the spectral properties of nonlinear transfer and dissipation of energy, and their effect on the resulting magnetic and electric field spectra. For typical solar wind parameters at 1 AU, it is found that about 30% of the nonlinear energy transfer occurring close to the electron gyroradius scale is in fact mediated by modes in the tail of the MHD cascade at $k_{\perp }{\rho }_i\lesssim 1$. Collisional dissipation is consistent with electron Landau damping and ion nonlinear phase mixing, resulting in significant dissipation at all scales in the kinetic range $k_{\perp }{\rho }_i\gtrsim 1$. Both transfer and dissipation thus occur on multiple coupled scales, which have to be retained for a comprehensive picture of the dissipation range in Alfvénic turbulence.