Measurements of shock velocity nonuniformities imprinted by the Nike laser*

With broad bandwidth and induced spatial incoherence (ISI) beam smoothing, the Nike KrF laser delivers most uniform illumination on targets among all existing high-energy lasers for inertial confinement fusion research. This gives particular interest to the laser-imprint levels that Nike actually provides, anticipating higher and more uniform ablation pressures in targets. We are building a high resolution 2D-VISAR^a on the Nike facility as a sensitive optical diagnostic for the laser imprint studies. Using a short pulse probe laser, the 2D-VISAR takes snapshots of 2-dimensional velocity fields at shock fronts. The velocity perturbations in the snapshot images will be used to evaluate the laser imprinting and its effect on target performance. We plan initial 2D-VISAR measurements on planar CH targets irradiated by various numbers of Nike main beams (1-44) to investigate multibeam irradiation effect on imprinting. This poster will present summary of the configuration of the 2D-VISAR with other target diagnostics including the line-VISAR and the 5^th harmonic grid image refractometer (Nike-GIR), and results of the initial measurements of imprint at Nike.

^a P.M. Celliers, et al, Rev. Sci. Instrum. 81, 035101 (2010).