Upstream parameter dependence of anisotropies in the ion distributions downstream of quasi-perpendicular shocks

Abstract

The reflection of part of the incident ions at quasi-perpendicular collisionless shocks results in highly structured and nonthermal ion distributions immediately downstream of such shocks. These distributions are unstable and lead to the generation of waves which in turn act to smooth out the distributions and thermalize the ions. Precisely which instabilities dominate the downstream turbulence depends sensitively on a number of parameters, such as the temperature anisotropy of the ion distributions and the velocity drift of the reflected ions relative to the directly transmitted/core ions. In this paper we conduct a series of one-dimensional hybrid simulations in order to estimate the values of these parameters immediately downstream of quasi-perpendicular shocks, and characterize their dependence on upstream conditions.