Plasma Expansion and Fine-Scale Instabilities in Hohlraum-Relevant Conditions

Experiments at the Omega EP laser facility investigate the expansion and instability dynamics of hohlraum-relevant plasmas. Filaments, formed by instabilities, can develop around laser spots, in conditions where both thermal and kinetic mechanisms contribute [1]. Previous work [2-4] has identified larger-scale filamentary features using proton radiography and our recent data provides additional information on density perturbations, revealing finer-scale structures. We use high-intensity lasers to drive expanding copper plasma bubbles into a low-pressure helium gas and diagnose the plasma using shadowgraphy and interferometry. These measurements reveal sharp interfaces and fine-scale filamentation structures with characteristic scales of 10–100 μm near the target surface.

We track the expansion of the plasma bubble and compare it to simulations performed with GORGON [5] and HYDRA [6]. While the overall shape of the bubble is well reproduced by both codes, the time-dependent expansion rate shows significant discrepancies. These results place new experimental constraints on magnetic field generation, thermal transport, and instability growth in laser-driven plasmas, with implications for hohlraum modeling in inertial confinement fusion.