Collisionless ablative plasma shocks

TL;DR

This paper investigates collisionless ablative plasma shocks, driven by thermal flux and ambipolar electric fields, highlighting their collisionless nature, shock structure, and ion heating mechanisms in plasma interfaces.

Contribution

It provides a detailed analysis of the physics governing collisionless ablative plasma shocks, emphasizing the role of ambipolar electric fields and collisionless ion heating.

Findings

Shock front width is set by upstream Debye length.

Shock speed correlates with downstream cold plasma sound speed.

Ion heating is highly efficient via collisionless mixing.

Abstract

An ablative plasma shock can emanate from the interface between a cold/dense plasma and a hot/dilute ambient plasma, where the plasma mean-free-path is much longer than the temperature gradient length. The shock is driven by thermal flux from the hot plasma into the cold plasma, primarily through tail electrons mediated by an ambipolar electric field, and it propagates into the ambient hot/dilute plasma. Since the collisional mean-free-path is usually much longer than the Debye length, the ablative plasma shock is mostly collisionless, with the shock front width set by the upstream hot plasma Debye length and the shock speed by the downstream cold plasma sound speed. The shock heating of ions is extremely efficient via collisionless mixing of upstream hot ions and downstream cold ions, both of which have been converted into shock-front-bound flows accelerated by the ambipolar electric field that has a deep potential well anchored inside the shock front.