Design of the removable shrouds for inertial-confinement-fusion cryotargets

The ablation of the laser-entrance hole (LEH) windows in the cryogenic target by a laser pulse would create plasma to prevent the subsequent laser from traversing through it into the hohlraums in inertial-confinement fusion (ICF) cryotarget experiments. The maximum areal density of absorbents on this window must be below 1 x 10-5 g/cm2 to meet the physical demand. A set of removable shrouds has been designed to prevent residual gasses in the cryogenic target system from condensing on the LEH windows in the cryotarget in combination with an open pumping and directional-condensation technology. The condensation rates of residual gas on the LEH windows of the cryotarget under different vacuum pressures were calculated to confirm the validity of the designed shrouds. A quartz crystal microbalance was used to evaluate the overall performance of the shrouds, which shows that the condensation rate can be limited below 8.7 x 10-8 g/(cm2 center dot h) at 15 K when the vacuum pressure in the cryogenic target system is 3.9 x 10-4 Pa. The removable shrouds have been successfully applied to laser ICF cryotarget experiments.