Dynamics of ultrafast heated radiative plasmas driven by petawatt laser lights

TL;DR

This study investigates how relativistic petawatt laser pulses heat heavy metal plasmas, focusing on radiation cooling effects and their impact on plasma dynamics using particle-in-cell simulations.

Contribution

The paper provides a detailed simulation analysis of radiation cooling effects in ultrafast heated silver plasmas driven by petawatt lasers, highlighting the role of X-ray emissions in plasma energy dissipation.

Findings

Radiation cooling significantly affects plasma energy evolution.

X-ray emissions are comparable to laser power at certain intensities.

Formation of a collisional shock at the plasma surface.

Abstract

A relativistic petawatt laser light can heat heavy metals over keV temperature isochorically and ionize them almost fully. Copious hard X-rays are emitted from the high-Z hot plasma which acts as X-ray sources, while they work as a cooling process of the plasma. The cooling process can affect on the creation of high energy density plasma via the interaction, however, the details are unknown. The X-ray spectrum depends on the plasma temperature, so that it is worthwhile to investigate the radiation cooling effects. We here study the isochoric heating of a solid silver foil irradiated by relativistic laser lights with a help of particle-in-cell simulations including Coulomb collisions, ionizations, and radiation processes. We have conducted a parameter survey varying laser intensity, $10^{18-20}\,\rm{W/cm^2}$, to check the cooling effects while keeping the incident laser energy constant. The silver plasma heated mainly by the resistive heating dissipates its energy by keV X-ray emissions in a picosecond time scale. The radiation power from the silver foil is found to be comparable to the incident laser power when the laser intensity is less than $10^{19}\,{\rm W/cm^2}$ under the constant energy situation. The evolution of the plasma energy density inside the target is then suppressed, due to which a highly compressed collisional shock is formed at the target surface and propagates into the plasma. The radiation spectra of the keV silver plasma are also demonstrated.