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

Abstract
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 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.