Uniform liquid-fuel layer produced in a cryogenic inertial fusion target by a time-dependent thermal gradient

Targets for inertial confinement fusion are cooled by cryogenic helium gas jets in an environment of room-temperature thermal radiation in an effort to obtain uniform condensed deuterium--tritium (DT) layers. A time-dependent thermal gradient obtained by ohmic heating of the upper nozzle is found to produce a transient state of uniformity in liquid DT just above its freezing point. A replaceable assembly of nozzles with heaters and thermometers is designed to be implemented in the target chamber of the OMEGA laser. Targets are held between the nozzles by spider webs which are attached to an independently positioned fixture. A flow of He of 6x10-5 g/s is sufficient to obtain the uniform DT layer, producing a background pressure in a test chamber of 0.5 mTorr. Targets are characterized interferometrically in two orthogonal views. Interferograms are compared with computed templates to determine the thickness and uniformity of the condensed layer