Direct-drive, hollow-shell implosion studies on the 60-beam, UV OMEGA laser system

Direct-drive implosion experiments have been performed on the University of Rochester’s 60-beam, 30 kJ, UV (351 nm) OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system to investigate the conditions at maximum compression of polymer–shell targets with zero- or low-pressure (⩽3 atm) gas fills. By using deuterium-bearing shells (CD), the imploded-core conditions have been diagnosed with both x-ray and neutron spectral measurements. The core electron temperature (kTe) and shell areal density (ρRshell) are determined from the emergent x-ray spectrum, while independent inferences of ρRshell are obtained from the measured primary (DD) and secondary (DT) neutron yields. Target performance was investigated for a range of beam-smoothing conditions [none to 0.25 THz-bandwidth smoothing by spectral dispersion along two dimensions (2-D SSD)] and a set of pulse shapes (1 ns square pulse to a 2.5 ns pulse with a 1:40 foot-to-main-pulse power ratio). The results have conclusively demonstrated the ability to compress targets to shell areal densities in the range of ∼60 to 130 mg/cm2.