Early-time measurements of laser-plasma conditions in OMEGA-upgrade ICF targets. Final report, April 1, 1998--January 31, 1999

All of the experimental results from OMEGA shots described here are from CY-1998 experiments under an (extended) FY-98 grant. This research involves fielding at LLE their two flat-field euv spectrographs in the 30--250 angstrom range, mainly utilizing on one o them a gated stripline microchannel plate as a time-resolved detector, with photographic recording. The experimental layout for the 1998 experiments is shown. During the week beginning May 3, 1998, the authors obtained 24 data shots over 4 days, and fielded both the time-gated extreme ultraviolet (euv) spectrograph mounted external to the target chamber, as well as their newly-constructed TIM-mounted euv spectrograph mounted closer to the target with time-integrated photographic recording on a trial basis. They also had available the LLE/LLNL streak x-ray spectrograph and x-ray imaging cameras. In this series, the first two shots appeared from the x-ray streak spectra to be normal in the sense that the spectral line emissions from the two coatings sequenced beginning with magnesium followed by aluminum as the coatings were vaporized. Unfortunately, on the following shots in this campaign it became increasingly apparent that conditions had changed radically, and later analyses showed that x-ray spectra lines from the deep aluminum undercoating appeared initially along with weak magnesium lines, indicating a premature vaporization of the magnesium heavier top layer. The second campaign in 1998 occurred during the week beginning October 18, 1998 and consisted of 21 data shots over two extended (12-hour) days following setup. For this series the authors again used their externally-mounted euv spectrography with time resolution and the x-ray streak spectrograph and imaging cameras. Much to their relief, it was immediately evident from the x-ray streak spectra obtained that significant ablation of the magnesium coatings by a (presumed) prepulse was not present, as it had been in the May campaign