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

A very smooth highly reflective coating on inertial fusion energy (IFE) targets is essential for direct-drive ignition. A gold/palladium (Au/Pd) alloy is sputter coated onto the surface of an IFE target. This provides a larger outward momentum of the material ablated by the ignition laser and improves the energy released 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 to be very durable and that any handling techniques, such as transferring from the layering system to the injector, must be gentle. The coatings were initially tested by physically impacting two targets together to simulate motion in a fluidized bed and 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, a titanium sublayer was coated between the plastic shell and the Au/Pd coating to strengthen the adhesion between the inner and outer layers. The initial results of the multilayered 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.