Detailed characterization of laboratory magnetized super-critical collisionless shock and of the associated proton energization

TL;DR

This paper presents experimental and simulation studies of magnetized collisionless shocks generated in laboratory conditions, revealing details of shock structure, plasma parameters, and proton acceleration mechanisms relevant to astrophysical phenomena.

Contribution

It provides the first detailed laboratory characterization of magnetized super-critical collisionless shocks and demonstrates the robustness of shock surfing acceleration for proton energization.

Findings

Shock is collisionless and super-critical.

Proton energization occurs via shock surfing acceleration.

Experimental results agree with hydrodynamic and kinetic simulations.

Abstract

Collisionless shocks are ubiquitous in the Universe and are held responsible for the production of non-thermal particles and high-energy radiation. In the absence of particle collisions in the system, theoretical works show that the interaction of an expanding plasma with a pre-existing electromagnetic structure (as in our case) is able to induce energy dissipation and allow for shock formation. Shock formation can alternatively take place when two plasmas interact, through microscopic instabilities inducing electromagnetic fields which are able in turn to mediate energy dissipation and shock formation. Using our platform where we couple a fast-expanding plasma induced by high-power lasers (JLF/Titan at LLNL and LULI2000) with high-strength magnetic fields, we have investigated the generation of magnetized collisionless shock and the associated particle energization. We have characterized the shock to be collisionless and super-critical. We report here on measurements of the plasma density, temperature, the electromagnetic field structures, and particle energization in the experiments, under various conditions of ambient plasma and B-field. We have also modeled the formation of the shocks using macroscopic hydrodynamic simulations and the associated particle acceleration using kinetic particle-in-cell simulations. As a companion paper of \citet{yao2020laboratory}, here we show additional results of the experiments and simulations, providing more information to reproduce them and demonstrating the robustness of our interpreted proton energization mechanism to be shock surfing acceleration.