Observation of ionization-mediated transition from collisionless interpenetration to collisional stagnation during merging of two supersonic plasmas

TL;DR

This study provides experimental evidence of a transition from collisionless to collisional behavior in merging supersonic plasmas, driven by increased ionization reducing mean free paths, with implications for plasma modeling.

Contribution

First experimental observation of ionization-driven transition from collisionless to collisional merging in supersonic plasmas, informing plasma collisionality and ionization models.

Findings

Collisionless interpenetration observed initially.

Transition to collisional stagnation due to increased ionization.

Data constrains models of plasma collisionality and ionization.

Abstract

We present space- and time-resolved experimental data of head-on-merging, supersonic plasma jets (of an argon/impurity mixture) in an initially collisionless regime for counter-streaming ions. The merging begins with collisionless interpenetration followed by a transition to collisional stagnation. The transition occurs due to an experimentally inferred rising mean-ionization level, which rapidly reduces the counter-streaming ion-ion mean free path. The measurements demonstrate a specific mechanism by which a collisionless interaction transitions to a collisional one and constrain collisionality and ionization models for plasmas with complex equation of state.