Symmetric inertial confinement fusion capsule implosions in a high-yield-scale double-Z-pinch-driven hohlraum on Z

Detailed radiation-hydrodynamics calculations indicate that the dual-63-MA Z-pinch high-yield (HY) 220-eV inertial confinement fusion concept [Phys. Plasmas 6, 2129 (1999)] may release 400 MJ of fusion yield, if pulse shaping, capsule preheat, and x-radiation drive uniformity can be acceptably controlled. Radiation symmetry is under detailed investigation in an advanced, 70-eV HY-scale scoping hohlraum [Phys. Rev. Lett. 88, 215004 (2002)] driven by the single 20-MA power feed of Sandia National Laboratories' Z accelerator. The time-averaged polar radiation asymmetry, <ΔI>/I, is inferred from direct distortion measurements of an imploding capsule's limb-darkened ('backlit') shell, via 6.7 keV point projection x-ray imaging. Thus far, <ΔI>/I has been measured at the 3.0±1.4 (%) level, on the best shots, in hohlraums (cylindrical) with length/radius ratios L/R of 1.61 and 1.69, either side of a L/R=1.66 predicted optimum for a zeroed P2 Legendre mode. Simulations suggest that when scaled to 220 eV with zeroed odd Legendre modes, relevant to the best fraction of shots on a dual power-feed HY accelerator, the increased hohlraum wall albedo would reduce the field asymmetry to the 0.9% level; thus approaching the uniformity requirements of high-yield ignition. Future studies at L/R=1.66 will include refinements in experimental methods and image analysis techniques (denoising), and the measured symmetry is anticipated to improve further