Collisionless shocks are ubiquitous structures in the universe that can be found in planetary magnetospheres, supernova remnants, and when galaxies merge inside a cluster. In a collisionless shock, collective fields provide complex nonlinear and kinetic interactions that can support collisionless/anomalous heating mechanisms in the plasma. Consequently, there is no generally accepted theory of particle energy partitioning and heating in collisionless shocks. Electron and ion temperatures are obtained by spacecraft measurement of planetary bow-shocks and analysis supernova remnant spectra exhibit large statistical variance of the inferred energy partition, and particle-in-cell simulations often cannot reproduce electron-ion temperature ratios measured in nature. Laboratory experiments offer a complementary approach to satellite measurements and astronomical observations.
In this talk, I will present results from magnetized collisionless shock laboratory experiments at conditions relevant to planetary bow-shocks (MA~ 8, ~ 3). We report the first laboratory observation of fully developed shocks (×3.6 compression ratio and a downstream region decoupled from the piston). The data indicate the presence of a foot ahead of the density discontinuity, where both electrons and ions exhibit significant super-adiabatic heating. Surprisingly, the downstream exhibits significant super-adiabatic heating of both species with electrons and ions in thermal equipartition, with an order-unity electron-ion downstream temperature ratio Te/Ti ~ 0.8. This temperature ratio is inconsistent with a combination of adiabatic compression and electron-ion collisional equilibration; thus, it provides the first laboratory evidence of collisionless anomalous heating in a fully developed perpendicular magnetized collisionless shock [1].
References
[1] Valenzuela-Villaseca, et al., “Laboratory measurements of energy partitioning and anomalous electron heating in magnetized, perpendicular collisionless shocks”, in review at The Astrophysical Journal. Preprint:
https://doi.org/10.48550/arXiv.2509.12164