Polar flux symmetry in Z-pinch-driven hohlraums using a self-backlit foam ball diagnostic

Summary form only given. In Z-pinch experiments on the Z accelerator, we are evaluating the feasibility of using a radiation-driven vacuum secondary hohlraum for indirect-drive ICF. To develop a system with the potential to scale to ignition and high yield, we must demonstrate a high degree of radiation flux symmetry at the capsule position. In initial experiments with single-sided illumination of the secondary, we have used a 5.0-mm-diameter low density foam ball imaged by a gated X-ray framing pinhole camera looking through a 6.5-mm tamped aperture to diagnose the large time-dependent asymmetry in polar radiation flux. For peak hohlraum radiation temperatures in the range of 70 100 eV, foams of about 50 mg/cc will support a transonic radiation front propagating with a sharp total transmission edge (combined foam self-emission and transmitted hohlraum wall backlight). The transmission edge can be tracked for comparison with radiation-hydrodynamics and 3D radiosity simulations.