Particle-in-cell simulations of collisionless shock formation via head-on merging of two laboratory supersonic plasma jets

TL;DR

This study uses particle-in-cell simulations to explore how merging laboratory plasma jets can form collisionless shocks, highlighting the influence of magnetic fields and jet parameters on shock generation.

Contribution

The paper presents detailed PIC and hybrid-PIC simulations of plasma jet merging, demonstrating conditions under which collisionless shocks form in laboratory settings.

Findings

Collisionless interactions occur at the jet merge region.

Magnetic fields of 0.1-1 kG can generate collisionless shocks.

Unmagnetized shocks are not formed at jet speeds up to 100 km/s.

Abstract

We describe numerical simulations, using the particle-in-cell (PIC) and hybrid-PIC code Lsp [T. P. Hughes et al., Phys. Rev. ST Accel. Beams 2, 110401 (1999)], of the head-on merging of two laboratory supersonic plasma jets. The goals of these experiments are to form and study astrophysically relevant collisionless shocks in the laboratory. Using the plasma jet initial conditions (density ~ 10^14-10^16 cm^(-3), temperature ~ few eV, and propagation speed ~ 20-100 km/s), large-scale simulations of jet propagation demonstrate that interactions between the two jets are essentially collisionless at the merge region. In highly resolved one- and two-dimensional simulations, we show that collisionless shocks are generated by the merging jets when immersed in applied magnetic fields (B ~ 0.1-1 kG). At expected plasma jet speeds of up to 100 km/s, our simulations do not give rise to unmagnetized collisionless shocks, which require much higher velocities. The orientation of the magnetic field and the axial and transverse density gradients of the jets have a strong effect on the nature of the interaction. We compare some of our simulation results with those of previously published PIC simulation studies of collisionless shock formation.