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 ( M A ∼ 8, M ms ∼ 4). We report the first observation of fully developed laboratory shocks that evolve for more than seven upstream ion gyroperiods and have a downstream region that extends for more than four shocked ion gyroperiods. We use Thomson scattering to measure electron and ion temperatures, plasma density, and flow speeds. We directly measure a compression ratio of 3.6 ± 0.3, consistent with shock jump conditions. A foot ahead of the shock exhibits superadiabatic electron and ion heating. The downstream electron temperature exceeds adiabatic and collisional electron–ion heating by ≈30%, implying significant collisionless anomalous electron heating. We find a downstream electron–ion temperature ratio T e ( d ) / T i ( d ) = 0.8 ± 0.3 , consistent with spacecraft observations but outside the range predicted by theory and numerical simulations.