Hypervelocity shrapnel damage assessment in the nif target chamber

Abstract

Summary In the National Ignition Facility (NIF) target chamber, hypervelocity shrapnel may be produced as the result of neutron and x-ray deposition in target and diagnostic support rods, photon shields, and other objects in the chamber. This shrapnel may pose a hazard for optics debris shields and chamber wall materials. This paper presents the results of a computational and experimental effort to develop a predictive methodology for assessing hypervelocity shrapnel damage. The methodology begins with computations of the size and velocity distributions for the shrapnel, which is typically computed to consist of sizes ranging from submicron to a few hundred micrometers and to span a velocity range from a few hundred m/s to tens of km/s. Damage algorithms were developed based on prior dimensional analyses and hydrocode cratering computations, hypervelocity data from the hypervelocity impact community, and laboratory impact data at a few hundred m/s. The predictions of the algorithms agreed well with the damage observed in the Lawrence Livermore National Laboratory NOVA and the French Commissariat a l'Energie Atomique PHEBUS laser facilities. The algorithms were then used to calculate damage maps in the NIF chamber for typical source conditions.