Pathways to Dissipation in Weakly Collisional Plasmas

Abstract

Observed turbulence in space and astrophysics is expected to involve cascade and subsequent dissipation and heating. Contrary to standard collisional fluid turbulence, the weakly collisional magnetized plasma cascade may involve several channels of energy conversion, interchange, and spatial transport, leading eventually to the production of internal energy. This paper describes these channels of transfer and conversion, collectively amounting to a complex generalization of the Kolmogorov cascade. Channels may be described using compressible magnetohydrodynamic (MHD) and multispecies Vlasov–Maxwell formulations. Key steps are conservative transport of energy in space, parallel incompressible and compressible cascades in scale, electromagnetic work on particles driving macroscopic and microscopic flows, and pressure–strain interactions, both compressive and shear-like, that produce internal energy. A significant contrast with the collisional case is that the steps leading to the disappearance of large-scale energy in favor of internal energy are formally reversible. This property motivates a discussion of entropy, reversibility, and the relationship between dissipation with collisions and in the Vlasov system without collisions. Where feasible, examples are given from MHD and Particle in Cell simulations and from MMS observations.

Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas

“…Further, all these results are consistent with kinetic scale simulations [22,38,39]. Besides the recent progress, how the turbulent energy is dissipated in all these almost collisionless plasma systems is still under debate and corresponds to one of the outstanding open questions in space plasma physics [20,40].…”

Kinetic entropy-based measures of distribution function non-Maxwellianity: theory and simulations

“…2016; Matthaeus et al. 2020). However, we are not aware of theoretical and/or computational studies which have put the entropy-based non-Maxwellianity measure on a firm footing.…”

“…Knowing and quantifying the non-Maxwellianity of a distribution function is potentially of great utility since dissipation is typically associated with the emergence of non-Maxwellian distribution functions and the collisional relaxation back towards Maxwellianity (e.g. Vaivads et al 2016;Valentini et al 2016;Matthaeus et al 2020). However, we are not aware of theoretical and/or computational studies which have put the entropy-based non-Maxwellianity measure on a firm footing.…”

Local and global properties of energy transfer in models of plasma turbulence

“…The interested reader is referred to two recent works that present, and discuss, the current state of our understanding of plasma heating and kinetic-scale turbulence from simulations, i.e. Matthaeus et al (2020) and Cerri, Groselj & Franci (2019).…”