Magnetic instability in a dilute circular rarefaction wave

TL;DR

This study uses 2D PIC simulations to investigate how a magnetic field can be generated in a circular rarefaction wave due to electron thermal anisotropy and instabilities, relevant to laser-ablated wire experiments.

Contribution

It demonstrates the development of magnetic fields via a Weibel-type instability in a circular rarefaction wave, linking plasma dynamics to experimental observations.

Findings

Magnetic fields grow through a Weibel-type instability.

Electron thermal anisotropy drives the instability.

Simulation results relate to laser-ablated wire experiments.

Abstract

The generation of a magnetic field in a circular rarefaction wave is examined in form of a 2D particle-in-cell (PIC) simulation. Electrons with a temperature of 32 keV are uniformly distributed within a cloud with a radius of 14.2 electron skin depths. They expand under their thermal pressure and carry with them the cold protons, which are initially concentrated in a hollow ring at the boundary of the electron cloud. The interior of the ring contains an immobile positive charge background that compensates for the electron charge. The protons expand in form of a circularly symmetric rarefaction wave and they extract energy from the electrons. A thermal anisotropy of the electrons develops and triggers through a Weibel-type instability the growth of TM waves within the plasma cloud, which acts as a wave guide. The changing cross section of this waveguide introduces a coupling between the TM wave and a TE wave and in-plane magnetic fields grow. The relevance of the simulation results to a previous experimental study of a laser-ablated wire is discussed.