A Method for Characterizing and Improving the Damage Resistance of the Outer Metallic Coatings on Inertial Fusion Energy Targets

Abstract

A very smooth, highly-reflective coating on IFE (Inertial Fusion Energy) targets is essential for direct-drive ignition. An Au/Pd (gold-palladium alloy) is sputter coated onto the surface of an IFE target to improve the energy release from the target compression and thermonuclear reaction. It is also necessary to reflect the black body infrared radiation experienced while traveling into the chamber and preserve the delicate frozen deuterium and tritium ice inside. The coating must remain intact, without any ?pinhole? defects, which requires it be very durable and any handling techniques, such as transfer from the layering system to the injector, be gentle. The coatings were initially tested by physically impacting two targets together to simulate motion in a fluidized bed where most of the damage is estimated to occur. The coatings were also tested in tension to better understand the adhesion of the coating. Variations in the coating parameters were explored and optimized to produce a low-stress, smooth coating of Au/Pd, which was found to have better resistance to damage than the current coatings. Additionally, several novel methods for improving the coating's resistance to damage were investigated. One example is coating a sub-layer between the plastic shell and the Au/Pd coating using titanium as the bond enhancer. The initial results of the multi- layered coating performed more than twice as well as the best standard Au/Pd coating previously tested. This shows promise for the use of an interlayer to promote better bonding of the outer metallic reflective coating to the plastic shell.