Target-induced damage considerations in the design of ICF diagnostics (abstract)

We have recently performed an empirical study of issues associated with target-induced damage, with emphasis on the next-generation NIF target chamber. However, some conclusions are also applicable to present day experimental diagnostics. We will discuss three topics: (1) degradation of the diagnostic due to the buildup of unwanted materials; (2) physical damage to the diagnostic from target debris; and (3) the potential for the diagnostic to create debris, which can cause subsequent damage to chamber optics. In the first category, we have measured both target material (Au,Cu) and ablated diagnostic material (Ta, Pb) which has subsequently redeposited on x-ray filters, changing their opacity. We have also measured the deposition of Al, from x-ray ablation from a nearby mounting fixture, onto a fused silica optic. Damage to diagnostics on Nova, sufficient to result in their failure, tends to be restricted to that caused by nonvaporized debris from large copper shields, gas fill tubes, etc. However, NIF targets will have a significantly larger impulse associated with the expanding gold hohlraum. We have measured the impulse associated with Nova hohlraums, for benchmarking code calculations. We will briefly discuss the implications of the third category in the design of NIF diagnostics.copyright 1997 American Institute of Physics