http://arxiv.org/abs/2002.11132
Collisionless shocks heat electrons in the solar wind, interstellar blast waves, and hot gas permeating galaxy clusters. How much shock heating goes to electrons instead of ions, and what plasma physics controls electron heating? We simulate 2-D perpendicular shocks with a fully kinetic particle-in-cell code. For magnetosonic Mach number $\mathcal{M}\mathrm{ms} \sim 1$-$10$ and plasma beta $\beta\mathrm{p} \lesssim 4$, the post-shock electron/ion temperature ratio $T_\mathrm{e}/T_\mathrm{i}$ decreases from $1$ to $0.1$ with increasing $\mathcal{M}\mathrm{ms}$. In a representative $\mathcal{M}\mathrm{ms}=3.1$, $\beta_\mathrm{p}=0.25$ shock, electrons heat above adiabatic compression in two steps: ion-scale $E_\parallel = \vec{E} \cdot \hat{b}$ accelerates electrons into streams along $\vec{B}$, which then relax via two-stream-like instability. Shock rippling also allows quasi-static shock-normal electric fields to heat electrons; we find that quasi-static fields generally contribute half of the electron heating beyond adiabatic compression.
A. Tran and L. Sironi
Thu, 27 Feb 20
18/51
Comments: 6 pages, 4 figures; re-submitted. Supplemental material at this http URL
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