Princeton Center for Heliophysics Seminar

Collisionless shocks are ubiquitous in space and astrophysical plasmas, where they often mediate conversion of flow energy into particle acceleration and heating. In hot and rarified (weakly collisional) plasmas, the energy dissipation must be provided by kinetic processes. Among those, plasma instabilities have long been considered the primary candidates. In this presentation, we will discuss results from a simulation study utilizing state-of-the-art fully kinetic simulations to assess the role of micro-instabilities on energy partition at quasi-perpendicular shocks. The study is motivated by observational data, which became available over the last decade. That data suggests that high-amplitude, high-frequency electric field fluctuations are present in spacecraft data in virtually every shock traversal where the required resolution is available, almost independent of the shock parameters. Yet, it currently remains unclear if these fluctuations play an essential role in shock dynamics. The simulations exhibit many of the instabilities present in the data, such as ion-acoustic and lower-hybrid oscillations, solitary structures (ion and electron holes), and whistler-branch modes. The origin of the instabilities is linked to dynamics of electron distribution across the shock. For the cases considered, the instabilities are not seen to significantly affect energy partition in the average sense but do produce significant local variations in particle energization.