title: NIF-scale re-emission sphere measurements of early-time Tr = 100 eV hohlraum symmetry (invited).
abstract: The indirect-drive National Ignition Campaign (NIC) proposes to set the first 2 ns 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 200 ps temporal, 50-100 microm spatial, and 30% spectral resolution. The sphere is driven by 70% NIC-scale vacuum Au hohlraums heated to Tr=100 eV using two cones per side laser beam illumination. The experiments have demonstrated the required accuracies of <3%P(2)/P(0) and <3%P(4)/P(0) Legendre mode flux asymmetry at both 900 and 1200 eV re-emission photon energies. The re-emission patterns at 900 and 1200 eV are also consistent with each other and their relative dependence on radiation temperature. We measured the P(2)/P(0) and P(4)/P(0) dependence to laser cone power ratio. View factor calculations are in agreement with the experimentally measured radiation flux and re-emit images when assuming 55% inner beam and 100 % outer beam coupling into x rays at the hohlraum wall.
authors.affiliation: Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA.
authors.forename: E L
authors.initials: EL
authors.lastname: Dewald
authors.forename: C
authors.initials: C
authors.lastname: Thomas
authors.forename: J
authors.initials: J
authors.lastname: Milovich
authors.forename: J
authors.initials: J
authors.lastname: Edwards
authors.forename: C
authors.initials: C
authors.lastname: Sorce
authors.forename: R
authors.initials: R
authors.lastname: Kirkwood
authors.forename: D
authors.initials: D
authors.lastname: Meeker
authors.forename: O
authors.initials: O
authors.lastname: Jones
authors.forename: N
authors.initials: N
authors.lastname: Izumi
authors.forename: O L
authors.initials: OL
authors.lastname: Landen