Non-adiabatic electron behaviour due to short-scale electric field structures at collisionless shock waves

TL;DR

This paper investigates how short-scale, high-amplitude electric field structures at collisionless shocks cause non-adiabatic electron heating, challenging traditional assumptions about shock heating mechanisms.

Contribution

It demonstrates that short-scale electric field structures induce non-adiabatic electron behavior and heating, highlighting the importance of their spatial location, a novel insight in shock physics.

Findings

Short-scale electric field structures cause electron heating that violates adiabatic invariants.

The spatial location of these structures significantly affects the extent of non-adiabatic behavior.

Such structures introduce a new relevant scale length in shock heating analysis.

Abstract

Under sufficiently high electric field gradients, electron behaviour within exactly perpendicular shocks is unstable to the so-called trajectory instability. We extend previous work paying special attention to shortiscale, high amplitude structures as observed within the electric field profile. Via test particle simulations, we show that such structures can cause the electron distribution to heat in a manner that violates conservation of the first adiabatic invariant. This is the case even if the overall shock width is larger than the upstream electron gyroradius. The spatial distance over which these structures occur therefore constitutes a new scale length relevant to the shock heating problem. Furthermore, we find that the spatial location of the short-scale structure is important in determining the total effect of non-adiabatic behaviour - a result that has not been previously noted.