Collapsing radiative shock experiments on the Omega Laser.

Abstract

Radiative shocks are notoriously difficult to produce in a laboratory setting, due to the extreme demands of the production of relatively high temperatures over sufficient extent for radiation and matter to interact. This dissertation describes a fundamental radiation hydrodynamics experiment, using a low-<italic> Z</italic> piston to drive a strong shock through low density gas, creating a driven, radiatively collapsed shock. Using 10 beams of the 60-beam Omega Laser facility at the University of Rochester, a low-<italic>Z</italic> disk is irradiated with an intensity of approximately 5 x 10<super>14</super> W/cm<super>2</super> in a 1 ns square pulse over a 1 mm spot size. The laser disturbance first shocks then accelerates the disk via laser ablation pressure, achieving velocities well over 200 km/sec. This accelerated piston drives a shock into gas, usually xenon. The strong shock heats the gas to several hundred eV, which then radiates away a significant amount of energy, leading the shocked plasma to collapse to very high compression. This experiment is compared to astrophysical systems with similar optical depth profiles. Radiative shocks are common in astrophysical settings, where it is easy to generate fast shocks in low-density media. This experiment has applications to laser-driven dynamic hohlraums, which would take advantage of the radiative shock as a smooth implosion source while still reaping the benefits of a converging geometry.