Demagnetized Electron Heating at Collisionless Shocks

TL;DR

This paper analyzes electron heating at Earth's collisionless bow shock, revealing that electron trajectories become chaotic due to magnetic and electric field fluctuations, affecting thermal heating and acceleration.

Contribution

It provides the first detailed measurements linking electron temperature variations to magnetic and electric field fluctuations at collisionless shocks.

Findings

Electron temperatures vary unpredictably, exceeding or falling below adiabatic expectations.

Average parallel and perpendicular electron heating are equal.

Chaotic electron trajectories are caused by large magnetic and electric field fluctuations.

Abstract

Seventy measurements of electron heating at the Earth's quasi-perpendicular bow shock are analyzed in terms of Maxwellian-temperatures obtained from fits to the core electrons that separate thermal heating from supra-thermal acceleration. The perpendicular temperatures are both greater and lesser than expected for adiabatic compression. The average parallel and perpendicular heating is the same. These results are explained because, over the electron gyroradius, $\delta B/B\sim 1$ and $e\delta \phi/T_e\sim 1$, so electron trajectories are more random and chaotic than adiabatic. Because density fluctuations are also large, trapping and wave growth in density holes may be important.