Modeling Temperature and Pressure Gradients During Cooling of Thin-Walled Cryogenic Targets

118 LLE Review, Volume 94 Introduction High-quality targets must be provided to achieve successful results from OMEGA cryogenic experiments.1 One type of target is a thin-walled polymer capsule with a fuel layer of solid deuterium (D2) or deuterium/tritium (DT) ice, approximately 100 mm thick, uniformly distributed on the inner wall of the capsule.2 To create the fuel layer, the capsule is placed in a room-temperature pressure vessel and slowly pressurized, filling the capsule by permeation through the polymer wall.3 The capsule is slowly cooled to the critical point (~38.3 K for D2) to first liquefy the gas, and then further cooled to freeze it. The mass of ice is made uniform through layering techniques.4 Because of the capsules’ fragile nature and the great amount of time required to fill them, the cooling process is a critical phase of operation for providing cryogenic targets.