Collisionless electrons in a thin high Mach number shock: dependence on angle and b

It is widely believed that electron dynamics in the shock front is essentially collisionless and determined by the quasistationary magnetic and electric ®elds in the shock. In thick shocks the electron motion is adiabatic: the magnetic moment is conserved throughout the shock and v? / B. In very thin shocks with large cross-shock potential (the last feature is typical for shocks with strong electron heating), electrons may become demagnetized (the magnetic moment is no longer conserved) and their motion may become nonadiabatic. We consider the case of substantial demagnetization in the shock pro®le with the small-scale internal structure. The dependence of electron dynamics and downstream distributions on the angle between the shock normal and upstream magnetic ®eld and on the upstream electron temperature is analyzed. We show that demagnetization becomes signi®cantly stronger with the increase of obliquity (decrease of the angle) which is related to the more substantial in ̄uence of the inhomogeneous parallel electric ®eld. We also show that the demagnetization is stronger for lower upstream electron temperatures and becomes less noticeable for higher temperatures, in agreement with observations. We also show that demagnetization results, in general, in non-gyrotropic down-stream distributions.