Long-lifetime, low-contamination metal beam dumps for NIF spatial filters Page: 3 of 13
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Long-lifetime, low-contamination metal beam dumps
for NIF spatial filters
Mary A. Norton, Charles D. Boley, James E. Murray, Kurt Sinz, and Kurt Neeb
University of California, Lawrence Livermore National Laboratory
P.O. Box 808, L-479, Livermore, CA 94550
The management of back reflections and leakage through the Pockels cell and
polarizer switch in the National Ignition Facility (NIF) beamlines requires robust beam
dumps that can operate unattended for thousands of shots within the confines of the
vacuum spatial filters. Off-line experiments and modeling have been used to investigate the
use of metal for these beam dumps. We conclude that a stainless steel beam dump will
have sufficient lifetime and will safely absorb fluences in the required range, from 1 J/cm2
to 4 kJ/cm2, at 1 pm.
The NIF laser architecture must accommodate efficient trapping of unwanted
beams that have their origin in Pockels cell leakage and target and/or pinhole back-
reflections. Since the NIF architecture uses angle multiplexing to make multiple passes
through the final amplifiers, certain locations are appropriate for separation of unwanted
beams from the main laser beam. These are within the vacuum spatial filters at and near
the pinhole planes. Consequently, the fluences which the dumps must absorb are quite
large, beyond the damage threshold of optical materials. We have used off-line tests,
modeling results, and NOVA shots to develop a robust beam dump concept for NIF,
capable of operation at more than 4 kJ/cm2 and having a lifetime greater than 1000 shots.
The origin of the unwanted beams and the location of the required beam dumps
can be seen in the schematic of the NIF architecture shown in Figure 1. The main beam is
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Boley, C D; Murray, J E; Neeb, K; Norton, M A & Sinz, K. Long-lifetime, low-contamination metal beam dumps for NIF spatial filters, article, October 30, 1998; California. (digital.library.unt.edu/ark:/67531/metadc626858/m1/3/: accessed October 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.