Producing Cryogenic Deuterium Targets for Experiments on OMEGA

AbstractThe 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-μm-thick outer plastic ablator and an inner ice layer that ranges from 80 to 100 μm thick. The smoothest ice layer possessed an average root-mean-square (rms) roughness of 1.2 μm, although values ranging from 2 to 4 μm are more typical. Implosion experiments achieved a maximum yield of 2.11 × 1011primary neutrons (70% of the clean one-dimensional yield) with an average areal density of 50 mg/cm2with a 1-ns square, high-adiabat (α = 25) laser pulse. Lower yields (1 × 1010primary neutrons) and higher areal densities (88 mg/cm2) were obtained using a lower-adiabat (α = 4) laser pulse. Better performance is expected once smoother ice layers (better than 2-μm average rms roughness) are positioned within 10 μm 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 μm.