Laboratory-scale Perpendicular Collisionless Shock Generation and Ion Acceleration in Magnetized Head-on Colliding Plasmas

TL;DR

This study uses large-scale particle-in-cell simulations to explore how magnetized collisionless shocks form and accelerate ions in laboratory conditions, revealing magnetic amplification and nonthermal ion spectra relevant to astrophysics.

Contribution

It presents the first realistic laboratory-scale simulation of perpendicular collisionless shocks with detailed magnetic amplification and ion acceleration mechanisms.

Findings

Formation of a perpendicular collisionless shock with fourfold density jump.

Significant magnetic field amplification, about 30 times the initial field.

Generation of nonthermal ion energy spectra via shock surfing acceleration.

Abstract

Magnetized collisionless shocks drive particle acceleration broadly in space and astrophysics. We perform the first large-scale particle-in-cell simulations with realistic laboratory parameters (density, temperature, and velocity) to investigate the magnetized shock in head-on colliding plasmas with an applied magnetic field of tens of Tesla. It is shown that a perpendicular collisionless shock is formed with about fourfold density jump when two pre-magnetized flows collide. This shock is also characterized by rapid increase of neutron yield, triggered by the beam-beam nuclear reactions between injected deuterons and ones reflected by the shock. Distinct from the shocks arising from the interaction of injected flows with a magnetized background, the self-generated magnetic field in this colliding plasmas experiences a significant amplification due to the increasing diamagnetic current, approximately 30 times of upstream magnetic field. Moreover, we find that ions, regardless of whether they pass through or are reflected by the shock, can gain energy by the shock surfing acceleration, generating a power-law energy spectrum. In addition, we also demonstrate that the shock mediated only by filamentation instability cannot be generated under the prevailing unmagnetized experimental parameters. These results provide a direct connection of astrophysical field amplification to the magnetized shock formation and nonthermal ion generation.