Dynamic convergent shock compression initiated by return current in high-intensity laser solid interactions

TL;DR

This paper explores how ultra-fast relativistic laser pulses induce convergent shock compression in solid wire targets through magnetic pressure and surface ablation, revealing new insights into high-pressure physics applications.

Contribution

It demonstrates the dominant shock compression mechanisms depend on target size and composition, and introduces a novel laser-driven platform for generating extreme pressures.

Findings

Magnetic pressure and surface ablation initiate shock compression.

The dominant mechanism varies with target radius and atomic number.

Experimental evidence of hydrogen compression via plasma expansion measurement.

Abstract

We investigate the dynamics of convergent shock compression in the solid wire targets irradiated by an ultra-fast relativistic laser pulse. Our Particle-in-Cell (PIC) simulations and coupled hydrodynamic simulations reveal that the compression process is initiated by both magnetic pressure and surface ablation associated with a strong transient surface return current with the density in the order of 1e17 A/m^2 and a lifetime of 100 fs. The results show that the dominant compression mechanism is governed by the plasma $\beta$, i.e., the ratio of the thermal pressure to magnetic pressure. For small radii and low atomic number Z wire targets, the magnetic pressure is the dominant shock compression mechanism. As the target radius and atomic number Z increase, the surface ablation pressure is the main mechanism to generate convergent shocks based on the scaling law. Furthermore, the indirect experimental indication of the shocked hydrogen compression is provided by measuring the evolution of plasma expansion diameter via optical shadowgraphy. This work could offer a novel platform to generate extremely high pressures exceeding Gbar to study high-pressure physics using femtosecond J-level laser pulses, offering an alternative to the nanosecond kJ laser pulse-initiated and pulse power Z-pinch compression methods.