Current Sheets and Collisionless Damping in Kinetic Plasma Turbulence

Abstract

We present the first study of the formation and dissipation of current sheets at electron scales in a wave-driven, weakly collisional, 3D kinetic turbulence simulation. We investigate the relative importance of dissipation associated with collisionless damping via resonant wave-particle interactions versus dissipation in small-scale current sheets in weakly collisional plasma turbulence. Current sheets form self-consistently from the wave-driven turbulence, and their filling fraction is well correlated to the electron heating rate. However, the weakly collisional nature of the simulation necessarily implies that the current sheets are not significantly dissipated via Ohmic dissipation. Rather, collisionless damping via the Landau resonance with the electrons is sufficient to account for the measured heating as a function of scale in the simulation, without the need for significant Ohmic dissipation. This finding suggests the possibility that the dissipation of the current sheets is governed by resonant wave-particle interactions and that the locations of current sheets correspond spatially to regions of enhanced heating.

Energy dissipation by whistler turbulence: Three-dimensional particle-in-cell simulations

“…2, who found current sheet heating to be several orders of magnitude more efficient than damping by kinetic Alfven waves, and with the less strongly driven results of Ref. 4, who concluded that We further quantify the intermittency in our simulations by showing that the PDFs of magnetic field increments depart more strongly from Gaussian distributions as the separation length decreases. The PDFs at short spatial separations are anisotropic between d rB?…”

“…Recent PIC simulations 2,3 have begun with a large-scale sheared flow configuration subject to the Kelvin-Helmholtz instability; the consequent long-wavelength turbulence undergoes a forward cascade developing electron-scale current sheets which efficiently dissipate the fluctuation energy via associated parallel electric fields. Recent gyrokinetic kinetic Alfv en turbulence simulations 4 driven by an oscillating antenna also show current sheet formation at electron gyroradius scales and suggest that the current structures are damped collisionlessly by resonant wave-particle interactions.…”

The Dynamical Generation of Current Sheets in Astrophysical Plasma Turbulence

“…Further exploration is required to determine whether the current sheet thickness is bounded by the simulation resolution or by the decoupling of ions from the electromagnetic fluctuations at rk 1 i . Note that plasma turbulence simulations ubiquitously show the development of current sheets (Matthaeus & Montgomery 1980;Meneguzzi et al 1981;Wan et al 2012;Karimabadi et al 2013;TenBarge & Howes 2013;Wu et al 2013;Zhdankin et al 2013), which sometimes appear to persist for a long time relative to other turbulent fluctuations on the scale of the thickness of the current sheet. This mechanism for current sheet generation may explain why these current sheets appear to persist for a long time because their lifetime is governed by the interaction of much larger-scale Alfvén waves.…”

Energy transfer, pressure tensor, and heating of kinetic plasma

“…The turbulence in most astrophysical contexts, on the other hand, is typically of weak collisionality, and frequently modeled as collisionless, and thus collisional (viscous and resistive) dissipation at small scales cannot emerge immediately. While various specific processes may contribute to conversion of energy from fields into random degrees of freedom, for example, wave-particle interactions (WPI) [16][17][18][19][20] and processes associated with coherent structures (CS) [21][22][23][24][25][26], are likely ingredients, but nevertheless an explicit dissipation function cannot at this moment be defined clearly for a collisionless system.…”