Laboratory measurements of energy partitioning and anomalous electron heating in magnetized, perpendicular collisionless shocks

Abstract

We present laboratory results on energy partitioning from supercritical, magnetized collisionless shock experiments (${\mathrm{M}}_{\mathrm{A}}\sim 8$, ${\mathrm{M}}_{\mathrm{ms}}\sim 4$). We report the first observation of fully-developed laboratory shocks that evolve for more than seven upstream ion gyration periods and have a downstream region that extends more than four shocked ion gyroperiods. Thomson scattering measurements are used to measure electron and ion temperatures, plasma density, and flow speeds. We directly measure a compression ratio of $3.6\pm 0.3$, consistent with shock jump conditions. A foot ahead of the shock exhibits super-adiabatic electron and ion heating. The downstream electron temperature has an $\approx 30\%$ excess above adiabatic and collisional electron-ion heating, implying significant collisionless anomalous electron heating. We find a downstream electron-ion temperature ratio $T_e^{(d)}/T_i^{(d)}=0.8\pm 0.3$, consistent with spacecraft observations but outside the range of predictions from theory and numerical simulations.

Main body: 8 pages, 5 Figures. Supplemental material: 12 pages, 5 figures