# Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors

## TL;DR

This study uses high-power laser experiments to generate counter-propagating radiative shocks in noble gases, enabling detailed analysis of shock dynamics, radiative precursors, and validation of numerical models relevant to astrophysical phenomena.

## Contribution

It introduces a new experimental setup for counter-propagating radiative shocks, allowing for 3-D effects and comparison with astrophysical shocks, with validation through simulations.

## Key findings

- Shocks propagated at approximately 80 km/s with strong radiative cooling.
- Radiative precursors extended further in higher atomic number gases.
- Good agreement between experimental data and radiative-hydrodynamic simulations.

## Abstract

We present results from new experiments to study the dynamics of radiative shocks, reverse shocks and radiative precursors. Laser ablation of a solid piston by the Orion high-power laser at AWE Aldermaston UK was used to drive radiative shocks into a gas cell initially pressurised between $0.1$ and $1.0 \ bar$ with different noble gases. Shocks propagated at {$80 \pm 10 \ km/s$} and experienced strong radiative cooling resulting in post-shock compressions of { $\times 25 \pm 2$}. A combination of X-ray backlighting, optical self-emission streak imaging and interferometry (multi-frame and streak imaging) were used to simultaneously study both the shock front and the radiative precursor. These experiments present a new configuration to produce counter-propagating radiative shocks, allowing for the study of reverse shocks and providing a unique platform for numerical validation. In addition, the radiative shocks were able to expand freely into a large gas volume without being confined by the walls of the gas cell. This allows for 3-D effects of the shocks to be studied which, in principle, could lead to a more direct comparison to astrophysical phenomena. By maintaining a constant mass density between different gas fills the shocks evolved with similar hydrodynamics but the radiative precursor was found to extend significantly further in higher atomic number gases ($\sim$$4$ times further in xenon than neon). Finally, 1-D and 2-D radiative-hydrodynamic simulations are presented showing good agreement with the experimental data.