Isolation and Phase-Space Energization Analysis of Non-Adiabatic Electron Heating in Collisionless Shocks

The conversion of supersonic flow energy into thermal energy and particle acceleration in supercritical collisionless shocks can excite additional phenomena that causes the system to deviate significantly from predictions using magnetohydrodynamics. Here, we focus on the non-adiabatic heating of electrons, a process that has not been strongly linked to any identified mechanism. Shocks with high enough Mach number induce instabilities that create waves which ripple or travel into the shock's precursor. These waves may be the cause for non-adiabatic heating of some electrons as they travel through the shock transition region due to wave-particle interactions. We analyze a fully kinetic 2D3V TRISTAN simulation of a collisionless shock with heliospheric-like parameters. We study this energy transfer from wave-particle interactions with the "Field-Particle Correlation" (FPC) technique in combination with the "Instability Isolation Method" (Brown et al. 2023). The FPC technique generates velocity-space signatures that show the rate of energy transfer in velocity space. The "Instability Isolation Method" separates the electromagnetic waves induced by instabilities from that of the bulk shock profile, transforms this separated quantity into wavenumber space using the wavelet transform, and measures the frequency of the waves in the system using Faraday's law to link it to an instability. We use the FPC technique with the fields of these inducted wave(s) to generate velocity-space signatures that show how energy is transferred by these waves. Thus, we isolate which mechanism is responsible for non-adiabatic heating and we create a diagnostic that shows specifically how electrons are heated non-adiabatically in this system.