Bow shock fragmentation driven by a thermal instability in laboratory-astrophysics experiments

TL;DR

This study demonstrates that radiative cooling induces thermal instabilities in laboratory-formed bow shocks, leading to their fragmentation, which models similar processes in astrophysical jets from young stellar objects.

Contribution

The paper provides experimental evidence of thermal instability-driven fragmentation in bow shocks, linking laboratory results to astrophysical phenomena.

Findings

Rapid development of small-scale non-uniformities in bow shocks

Thermal instability triggered by radiative cooling causes shock fragmentation

Experimental results align with theoretical cooling function analysis

Abstract

The role of radiative cooling during the evolution of a bow shock was studied in laboratory-astrophysics experiments that are scalable to bow shocks present in jets from young stellar objects. The laboratory bow shock is formed during the collision of two counter-streaming, supersonic plasma jets produced by an opposing pair of radial foil Z-pinches driven by the current pulse from the MAGPIE pulsed-power generator. The jets have different flow velocities in the laboratory frame and the experiments are driven over many times the characteristic cooling time-scale. The initially smooth bow shock rapidly develops small-scale non-uniformities over temporal and spatial scales that are consistent with a thermal instability triggered by strong radiative cooling in the shock. The growth of these perturbations eventually results in a global fragmentation of the bow shock front. The formation of a thermal instability is supported by analysis of the plasma cooling function calculated for the experimental conditions with the radiative packages ABAKO/RAPCAL.