Magnetic field amplification by the Weibel instability at planetary and astrophysical high-Mach-number shocks

TL;DR

This paper investigates how the Weibel instability amplifies magnetic fields in high-Mach-number collisionless shocks using large-scale particle-in-cell simulations, with results consistent with spacecraft observations at Saturn.

Contribution

It demonstrates the role of the ion-ion two-stream Weibel instability in magnetic field amplification at planetary and astrophysical shocks, supported by simulation and spacecraft data.

Findings

Magnetic field is amplified at the shock transition due to the Weibel instability.

The magnetic-field strength correlates with the Alfvénic Mach number.

Simulation results agree with in-situ measurements at Saturn's bow shock.

Abstract

Collisionless shocks are ubiquitous in the Universe and often associated with strong magnetic field. Here we use large-scale particle-in-cell simulations of non-relativistic perpendicular shocks in the high-Mach-number regime to study the amplification of magnetic field within shocks. The magnetic field is amplified at the shock transition due to the ion-ion two-stream Weibel instability. The normalized magnetic-field strength strongly correlates with the Alfv\'enic Mach number. Mock spacecraft measurements derived from PIC simulations are fully consistent with those taken in-situ at Saturn's bow shock by the Cassini spacecraft.