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Proceedings Paper

Constraints on target chamber first wall and target designs that will enable NIF debris shields to survive
Author(s): Alan K. Burnham; Michel Gerassimenko; J. M. Scott; Jeff F. Latkowski; Pamela K. Whitman; Francois Y. Genin; Wilthea Hibbard; P. F. Peterson; R. E. Tokheim; D. R. Curran
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Paper Abstract

The NIF target chamber interior materials and target designs themselves have to be compatible with survival of the final- optics debris shields. To meet the planned maintenance and refinishing rate, the contamination of the debris shields cannot exceed about 1 nm equivalent thickness per shot of total material. This implies that he target mass must be limited to no more than 1 gram and the ablated mass released to the chamber from all other components must not exceed 3 grams. In addition, the targets themselves must either completely vaporize or send any minor amounts of shrapnel towards the chamber waist to prevent excessive catering of the debris shields. The constraints on the first-wall debris will remobilize at a rate fast enough to require cleaning every 3 weeks, about three times more frequent than possible with planned robotics. Furthermore, a comparison of ablatants from B4C and stainless-steel louvers suggest that remobilization of target debris by x-rays will be greater than that of the base material in both cases, thereby reducing the performance advantage of clean B4C over much cheaper stainless steel. Neutronics calculations indicate that activation of thin Ni-free stainless steel is not a significant source of maintenance personnel radiation dose. Consequently, the most attractive first wall design consists of stainless-steel louvers. Evaluation of various unconverted-light beam dump designs indicates that stainless steel louvers generate no more debris than other matrices, so one single design can serve as both first wall and beam dumps, eliminating beam steering restrictions caused by size and location of the beam dumps. One reservation is that the allowable contamination rate of the debris shield is not yet completely understood. Consequently, it is likely that either a protruding beam tube, a rapid post-shot gas purge of the final optics assembly, or thin polymeric pre-shield will be required to prevent low-velocity contamination from reaching the debris shield.

Paper Details

Date Published: 23 July 1999
PDF: 10 pages
Proc. SPIE 3492, Third International Conference on Solid State Lasers for Application to Inertial Confinement Fusion, (23 July 1999); doi: 10.1117/12.354187
Show Author Affiliations
Alan K. Burnham, Lawrence Livermore National Lab. (United States)
Michel Gerassimenko, Lawrence Livermore National Lab. (United States)
J. M. Scott, Univ. of California/Berkeley (United States)
Jeff F. Latkowski, Lawrence Livermore National Lab. (United States)
Pamela K. Whitman, Lawrence Livermore National Lab. (United States)
Francois Y. Genin, Lawrence Livermore National Lab. (United States)
Wilthea Hibbard, Lawrence Livermore National Lab. (United States)
P. F. Peterson, Univ. of California/Berkeley (United States)
R. E. Tokheim, SRI International (United States)
D. R. Curran, SRI International (United States)

Published in SPIE Proceedings Vol. 3492:
Third International Conference on Solid State Lasers for Application to Inertial Confinement Fusion
W. Howard Lowdermilk, Editor(s)

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