Streaked extreme ultraviolet imaging of the motion of low-Z foam buffered indirectly driven intermediate and high-Z payloads

Results of experiments conducted at the Central Laser Facility (Rutherford Appleton Laboratory), illustrating the efficacy of utilizing a combination of transonic and subsonic ablation to increase the impulse delivered to an indirectly driven payload, are reported. Extreme ultraviolet imaging has been utilized to map the trajectory of the rear surface of an accelerating payload driven by a hohlraum with a peak energy-density-equivalent radiation temperature of around 130 eV. Payloads comprising an approximately 30-mu m-thick solid-density plastic foil doped with chlorine, both with and without a gold flashing on the driver-facing surface, were accelerated by a combination of subsonic x-ray ablation of the rear surface of the payload and either subsonic, transonic, or supersonic ablation in a hohlraum facing low-density foam layer in intimate contact with the payload. Two different thicknesses of foam layer were incorporated in the experiment - 150 and 200 mu m - in addition to a range of different foam densities from 30 to 100 mg/cc. It was observed that the maximum impulse was delivered in the case where the ablation wave propagation was approximately transonic in the foam layer. In such cases the impulse delivered to the payload was significantly greater than that achieved by direct (subsonic) ablation of the payload.