Collisional-like dissipation in collisionless plasmas

Abstract

When collisions are strong in a magnetized plasma, standard closures provide simple representations of dissipation in terms of coefficients of viscosity and resistivity. In the opposite limit of weak collisions, the analogous physical effects that lead to dissipation are present, but the simple approximations to describe them, the closures, are not available in general. But how different are these relationships when collisions are absent? Here, we inquire as to whether the collisionless case admits statistical relationships analogous to the viscous and resistive closures found in collisional plasma. We employ kinetic particle-in-cell simulations of proton–electron plasma as well as in situ observations from the Magnetospheric Multiscale Mission, to examine analogous viscous-like and resistive-like scaling in the weakly collisional regime. Rather surprisingly, we find that, on average, the collisionless cases do exhibit dissipation behavior very similar to the collisional plasmas. It is of theoretical significance that the relationships found are statistical and not deterministic as they are when collisional closures are enforced.