Observations of Pressure Anisotropy Effects within Semi-Collisional Magnetized-Plasma Bubbles

TL;DR

This paper experimentally verifies that pressure anisotropy significantly influences magnetic field dynamics in semi-collisional plasmas, affecting magnetic reconnection and field redistribution in high-energy-density physics regimes.

Contribution

It demonstrates the importance of anisotropic pressure effects in semi-collisional plasmas, a factor often neglected, through experimental, modeling, and analytical approaches.

Findings

Pressure anisotropy reduces the magnitude of reconnecting magnetic fields.

Magnetic fields are advected by Nernst flows influenced by pressure anisotropy.

Anisotropic pressure effects are crucial for magnetic field redistribution in semi-collisional plasmas.

Abstract

Magnetized plasma interactions are ubiquitous in astrophysical and laboratory plasmas. Various physical effects have been shown to be important within colliding plasma flows influenced by opposing magnetic fields, however, experimental verification of the mechanisms within the interaction region has remained elusive. Here we discuss a laser-plasma experiment whereby experimental results verify that Biermann battery generated magnetic fields are advected by Nernst flows and anisotropic pressure effects dominate these flows in a reconnection region. These fields are mapped using time-resolved proton probing in multiple directions. Various experimental, modelling and analytical techniques demonstrate the importance of anisotropic pressure in semi-collisional, high-$\beta$ plasmas, causing a reduction in the magnitude of the reconnecting fields when compared to resistive processes. Anisotropic pressure dynamics are crucial in collisionless plasmas, but are often neglected in collisional plasmas. We show pressure anisotropy to be essential in maintaining the interaction layer, redistributing magnetic fields even for semi-collisional, high energy density physics (HEDP) regimes