NIF-scale re-emission sphere measurements of early-time Tr=100 eV hohlraum symmetry (invited)

The indirect-drive National Ignition Campaign (NIC) proposes to set the first 2ns of hohlraum radiation symmetry by observing the instantaneous soft x-ray re-emission pattern from a high-Z sphere in place of the ignition capsule. To assess this technique under NIC conditions, we used the Omega Laser Facility to image the re-emission of Bi coated spheres with 200ps temporal, 50–100μm spatial, and 30% spectral resolution. The sphere is driven by 70% NIC-scale vacuum Au hohlraums heated to Tr=100eV using two cones per side laser beam illumination. The experiments have demonstrated the required accuracies of <3%P2∕P0 and <3%P4∕P0 Legendre mode flux asymmetry at both 900 and 1200eV re-emission photon energies. The re-emission patterns at 900 and 1200eV are also consistent with each other and their relative dependence on radiation temperature. We measured the P2∕P0 and P4∕P0 dependence to laser cone power ratio. View factor calculations are in agreement with the experimentally measured radiation flux and re-emi...