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 .