Direct-Drive Implosion Experiments with Enhanced Beam Balance on the OMEGA Laser

Direct-drive implosions (e.g., 1-THz SSD) on OMEGA are now regularly performed with enhanced single-beam uniformity. To date, the beam power balance has been determined from a set of pickoffs, which are cross-calibrated to full beam calorimeters, and a device that measures the beam transport to the target chamber center (standard beam balance). A new technique has been implemented that determines the beam's peak intensities on a full-power target shot by simultaneously measuring the x-ray flux produced by all 60 beams seen separated on a 4-mm-diam, Au-coated spherical target. Up to nine x-ray pinhole camera images are electronically recorded per shot from which variations in peak intensities are determined, taking into account view angle and x-ray conversion efficiency. The observed variations are then used to correct the beam energies to produce a more uniform irradiation (enhanced beam balance). Results of implosion experiments with enhanced beam balance and comparisons to experiments with standard beam balance will be presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.