Cryogenic-laser-fusion target implosion studies performed with the OMEGA uv-laser system

A series of direct-drive laser-fusion implosion experiments was performed on cryogenically cooled, DT-filled glass microballoons with the OMEGA 24-beam uv (351-nm) laser system. The targets consisted of glass microballoons having radii of 100 to 150 {μ}m, wall thicknesses of 3 to 7 {μ}m, filled with DT gas at pressures of 75 to 100 atm. The targets were cooled to below the freezing point of DT, in situ, by a cryogenic target system. The targets were irradiated by approximately 1 to 1.2 kJ of uv light in 650-ps Gaussian pulses. The on-target irradiation uniformity was enhanced for these experiments by the use of distributed phase plates, which brought the estimated irradiation nonuniformities to {~}12% (σᵣₘₛ). Target performance was diagnosed by an array of x-ray, plasma, and nuclear instruments. The measured target performance showed {~}70% absorption, thermonuclear yields of 10⁶ to 10⁸ neutrons, and final fuel areal densities of 20 to 40 mg/cm² for the optimum targets examined in these experiments. Fuel densities at the time of thermonuclear neutron production, inferred from direct measurements of the fuel areal density, were in the range of 20 to 50 g/cm³ (100 to 200 times the density of liquid DT) for the optimum targets.