Producing Cryogenic Deuterium Targets for Experiments on OMEGA

The OMEGA cryogenic target handling system provides deuterium-filled cryogenic targets for direct-drive implosion experiments. The targets are 0.9 mm in diameter with a 3-m-thick outer plastic ablator and an inner ice layer that ranges from 80 to 100 m thick. The smoothest ice layer possessed an average root-mean-square (rms) roughness of 1.2 m, although values ranging from 2 to 4 m are more typical. Implosion experiments achieved a maximum yield of 2.11 × 10¹¹ primary neutrons (70% of the clean one-dimensional yield) with an average areal density of 50 mg/cm² with a 1-ns square, high-adiabat ( = 25) laser pulse. Lower yields (1 × 10¹⁰ primary neutrons) and higher areal densities (88 mg/cm²) were obtained using a lower-adiabat ( = 4) laser pulse. Better performance is expected once smoother ice layers (better than 2-m average rms roughness) are positioned within 10 m of where the laser beams are pointed. Currently, the offset between the target's location and where the laser beams are pointing at the moment of implosion is 14 to 60 m.