Time-resolved absorption in cryogenic and room-temperature direct-drive implosions

Time-dependent and time-integrated absorption fractions are inferred from scattered-light measurements in room-temperature and cryogenic direct-drive-implosion experiments on OMEGA. The measurements agree reasonably well with hydrodynamic simulations that include nonlocal electron-heat transport. Discrepancies in the time-resolved scattered-light spectra between simulations and experiments remain for complex laser pulse shapes, indicating beam-to-beam energy transfer and commensurate coupling losses. Time-resolved scattered-light spectra near omega/2 and 3 omega/2 as well as time-resolved hard-x-ray measurements indicate the presence of a strongly driven two-plasmon-decay (TPD) instability at high intensities that may influence the observed laser light absorption. Experiments indicate that energetic electron production due to the TPD instability can be mitigated with high-Z-doped plastic shells. (c) 2008 American Institute of Physics.