Reducing deuterium-tritium ice roughness by electrical heating of the saturated vapor

High gain targets for inertial confinement fusion (ICF) contain a layer of deuterium-tritium (DT) ice which surrounds a volume of DT gas in thermal equilibrium with the solid. The roughness of the cryogenic fuel layer inside of ICF targets is one of the sources of imperfections which cause implosions to deviate from perfect one dimensional performance. Experiments at Lawrence Livermore National Laboratory have shown that applying a heat flux across the inner surface of a hydrogen layer such as that inside an ICF target reduces the intrinsic roughness of the surface. We have developed a technique to generate this heat flux by applying and electric field to the DT vapor in the center of these shells. This vapor has a small but significant conductivity due to ionization caused by beta decay of tritium in the vapor and the solid. We describe here experiments using a 1.15 GHz cavity to apply an electric field to frozen DT inside of a sapphire test cell. The cell and cavity geometry allows visual observation of the frozen layers

Characterization of D-T cryogenic layer formation in a Beryllium capsule using X-ray phase contrast imaging

Copper-doped beryllium capsules filled with cryogenic deuterium and tritium (D-T) fuel layers offer many technical and manufacturing advantages for Inertial Confinement Fusion. However, characterizing the frozen fuel layer in such targets is challenging since traditional x-ray radiographic techniques, which rely on absorption for image contrast, cannot provide sufficient contrast to image the low-Z D-T fuel layer in these targets. In this research, we employ x-ray phase contrast imaging (XPCI), which relies on gradients in the object's phase, to produce image contrast. We find that XPCI has sufficient sensitivity to characterize the D-T cryogenic layers in an ignition-scale Be(Cu) capsule. A Be(Cu) capsule is filled with liquid D-T via a small fill-tube, and is kept at a uniform temperature below the D-T triple point in a cryostat designed to produce spherical isotherms. A very uniform spherical D-T ice layer ($<$ 1.5 $\mu$m RMS roughness) is formed within the capsule after a few hours due to heating by beta-decay of the tritium. Studies performed for D-T layer uniformity show an increase in surface roughness as the temperature is lowered. We discuss the source and detector characteristics necessary to obtain high quality XPCI images of the D-T layer, wave-propagation modeling of the image formation process, and image analysis

Nuclear spin polarization of solid deuterium-tritium

It appears that parallel alignment of deuteron and triton magnetic moments increases the cross section of the nuclear reaction T(d,n) He/sup 4/ by 50%, thereby promising a laser driver of perhaps half the original energy. Both ''brute-force'' and dynamic nuclear polarization are considered, and the many potential problems of the latter are considered. High nuclear polarization by the dynamic technique requires a small nucleus-to-unpaired electron ratio, a long longitudinal nuclear relaxation time and a short longitudinal electron relaxation time. Normal D-T is shown to be inadequate, and enriched and possibly very pure molecular DT will be required. The key variable is the nuclear relaxation time, which can either depend on the interaction with rotationally excited impurity molecules or on paramagnetic defects formed by the tritium radiation. Radiation-induced DT decomposition and rotational catalysis will combat one another to affect the DT purity. The expected atom density and fractionation effects are considered. There exists one frequency at which both D and T atoms can be pumped

Status of cryogenic layering for NIF ignition targets

Recent advances in cryogenic layering include the development of a self-contained and self-filling hohlraum, application of phase contrast x-ray measurements for ice layer characterization, and an ice layer achieved with beta-layering which meets the NIF specification for surface roughness at 1.5 K below the triple point. In addition, recent results on target integration in a hohlraum show effective layer control using heaters on the hohlraum