On-axis Hohlraum Radiography associated with N-Waves in Stellar Atmospheres.

The propagation of weak shocks in a stellar atmosphere, in conjunction with the high x-ray flux cannot be well-described using weak-shock theory. Experiments performed at the LLE OMEGA laser attempt to study shock dynamics similar radiation conditions. Point-projection radiography was performed along the axis of a 160eV hohlraum, illuminating the structures formed by the ablation of a 0.2mm annular slot in a solid Ta disc. Diagnosed whilst laser-driven, the platform also enables quantitative measurements of x-ray flow through high-Z foam slot. Backlit images of the radiatively-driven slot show complex `bubble-like' features at the intersection of ablation fronts. Despite the 3D aspects of the experiment, 2D simulations, using the radiation-hydrodynamics code are an excellent qualitative match to the data, demonstrating that structures result from a high pressure spike that forms from the colliding ablation fronts driving a blast wave-like expansion into the dense stagnation region.