Ogden Sterling Jones

High-density carbon ablator ignition path with low-density gas-filled rugby hohlraum

A recent low gas-fill density (0.6 mg/cc 4He) cylindrical hohlraum experiment on the National Ignition Facility has shown high laser-coupling efficiency (>96%), reduced phenomenological laser drive corrections, and improved high-density carbon capsule implosion symmetry [Jones et al., Bull. Am. Phys. Soc. 59(15), 66 (2014)]. In this Letter, an ignition design using a large rugby-shaped hohlraum [Amendt et al., Phys. Plasmas 21, 112703 (2014)] for high energetics efficiency and symmetry control with the same low gas-fill density (0.6 mg/cc 4He) is developed as a potentially robust platform for demonstrating thermonuclear burn. The companion high-density carbon capsule for this hohlraum design is driven by an adiabat-shaped [Betti et al., Phys. Plasmas 9, 2277 (2002)] 4-shock drive profile for robust high gain (>10) 1-D ignition performance and large margin to 2-D perturbation growth.

Influence of Cocktail Material Parameters on Indirect Drive Holhraum Performance

Summary form only given. Indirect drive performance for inertial confinement fusion depends to a large degree on the ability to mitigate wall losses in the hohlraum. One approach to do this is based on the use of hohlraum wall materials with overlapping absorption bands to absorb and re-emit the radiation that otherwise would be lost. Albedos for various combinations of these materials, so-called cocktails, have been calculated and a mixture of U, Dy and Au has been determined to be the best candidate. However, these calculations are based on published values of heat capacity and opacity and do not take into account possible material oxidation. In order to obtain accurate material data and to test the influence of oxygen two experimental campaigns were designed for the Omega laser facility in Rochester. The first experiment uses a laser energy of 7 kJ to heat a halfraum to a radiation temperature of 250 eV. The backwall of the half hohlraum consists of a split foil arrangement of two different materials and the re-emission characteristics and the burn through time of the foils are measured using framing and streak cameras. Using foils of each material and a combination of both materials allows us to determine heat capacity and opacity for each material. The 2nd campaign uses 20 kJ of laser energy to drive Au and cocktail hohlraums. Cocktail materials with varying oxygen content are tested and the difference in soft X-ray drive is measured using a soft X-ray spectrometer (DANTE). Experimental results will be presented testing our understanding of high-Z cocktail radiation properties