Counter-Propagating Laser Produced Radiative Shocks at the Orion Laser Facility
Résumé
The Orion high-power laser facility at AWE Aldermaston, UK, was used to produce hyper-sonic (M>>1) radiative shocks in a variety of noble gases. These experiments aimed to study the radiative precursor, a heat and ionization wave preceding the shock front and, for the first time, the dynamics of colliding, counter propagating radiative shocks. Laser ablation of a piston, at intensities of ~6x1014 W/cm2, drove counterpropagating shocks, with velocities between 60 km/s and 120 km/s, into a gas cell, filled to pressures between 0.1 bar and 1.0 bar. Targets were 4mm long octagonal gas cells, produced by SciTech Precision, with a diameter of 8mm to remove the effect of wall shocks. X-ray backlighting and optical self-emission streak Imaging were used to image the shock front and collision dynamics. Multi-frame and streaked interferometry were used to image the radiative precursor and determine its electron density. These experiments compared the shock and collision dynamics in different gases (e.g. Ne, Ar, Kr, Xe), maintaining a constant mass density in order to keep the hydrodynamics in the shock consistent while varying the strength of the radiative precursor losses. In some cases the shocks exhibited features suggesting the formation of hydrodynamic or radiative instabilities. The experimental data is in good agreement with 2-D numerical radiative-hydrodynamic simulations and provides a new benchmark for codes to be tested against. Project supported by Orions Academic Access Programme (through AWE and CLF), and in part by the Royal Society, and by EPSRC through a DTA Scholarship and by Labex PLAS@PAR (ANR-11-IDEX-0004-02). The authors would like to acknowledge the help and support from the staff at AWE Aldermaston.