Debris and Shrapnel
A variety of targets are fielded on NIF, from thin foils to large hohlraums with x-ray and unconverted light shields. These targets are subjected to a wide range of laser conditions. The laser interaction with the target ablates some of the target material to create plasma and debris, and for some conditions, shrapnel is generated. The debris and shrapnel may impact the debris shields, potentially causing damage that can grow on subsequent laser shots. In addition, diagnostics that experience large x-ray fluences, plus the target positioner and the first wall material in the target chamber, may all become sources of debris and shrapnel.
Simulation tools have been developed and benchmarked against facility data to predict the impact of specific targets on the NIF target chamber. Whenever an experimental campaign calls for a target design with a new feature, the Debris and Shrapnel Working Group performs a risk assessment and experimental modeling is performed to understand debris and shrapnel generation. Present guidance for target design is that the target should not produce more than 5–10 mg of shrapnel per shot and 300 mg of other particulates.