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

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 ± 10 km/s and experienced strong radiative cooling resulting in post-shock compressions of ×25 ± 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 (∼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

Analysis of microscopic properties of radiative shock experiments performed at the Orion laser facility

“…In the experiments [27, 28] , optical and X-ray diagnostics were fielded to study the plasma in the transverse direction to the direction of propagation of the radiative shocks. Therefore, radiation emitted from either the shocked material or from the radiative precursor will have to pass through regions of the radiative precursor with different temperatures.…”

“…Furthermore, the simulations also show the shock front as a rippled layer (see Figures 1(b) and 1(c)). Both phenomena reflect the spatial variations in mass density due to the growth of hydrodynamic instabilities [28] . Due to the strongly radiative nature of these shocks, this could be thermal instabilities.…”

“…New experiments have been recently performed to investigate the collision and interaction of two counter-propagating piston-driven radiative shocks [26][27][28][29] and their radiative precursors. These experiments open new applications in 2 R. Rodríguez et al the area of laboratory astrophysics, such as the study of reflected and transmitted radiative shock and the interaction of a radiative shock with a denser medium in astrophysics scenarios, and were conducted at the Prague Asterix Laser System (PALS) [30] and Orion high-power laser [31] facilities.…”

Inverse Liner Z-Pinch: An Experimental Pulsed Power Platform for Studying Radiative Shocks

“…It is possible to produce radiative shocks in laboratory experiments using lasers focused onto a pin embedded in a gas [9], a cluster gas [10]- [12], or a piston attached to a gas cell [13]- [21]. Radiative shocks have also been produced on pulsed power generators using imploding liners with an internal gas fill [22]- [24].…”

Design and fabrication of gas cell targets for laboratory astrophysics experiments on the Orion high-power laser facility

“…One such development that has been delivered is the implementation of a gas-filled microtarget capability. This was developed in response to an AWE academic access experiment [2, 3] carried out by a consortium led by Imperial College London and drawing on knowledge from AWE, Imperial College London, Observatoire de Paris and RAL, a capability was introduced and then transferred to RAL for the user community access for CLF experiments.…”