Hypervelocity shrapnel damage assessment in NIF target chamber

In the National Ignition Facility (NIF) target chamber, hypervelocity shrap nel 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 cham ber. This shrapnel may pose a hazard for optics debris shields and chamber wall materials. This paper presents the results of a computational and expe rimental effort to develop a predictive methodology for assessing hypervelo city 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 t o span a velocity range from a few hundred m/s to tens of km/s. Damage algo rithms were developed based on prior dimensional analyses and hydrocode cra tering computations, hypervelocity data from the hypervelocity impact commu nity, and laboratory impact data at a few hundred m/s. The predictions of t he algorithms agreed well with the damage observed in the Lawrence Livermor e 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. (C) 1999 Elsevier S cience Ltd. All rights reserved.