The goal of the European laser fusion project, is to build an engineering facility for repetitive laser operation (HiPER 4a) and later a fusion reactor (HiPER 4b). A key aspect for laser fusion energy is the final optics. At the moment, it is based on silica transmission lenses located 8 m away from the chamber center. Lens lifetime depends on the irradiation conditions. We have used a 48 MJ shock ignition target for calculations. We have studied the thermo-mechanical effects of ions and X-rays on the lenses. Ions lead to lens melting and must therefore be mitigated. On the other hand, X-rays (~1% of the energy) does not produce either a significant temperature rise or detrimental stresses. Finally, we calculated the neutron flux and gamma dose rate on the lenses. Next, based on a simple model we studied the formation of color centers in the sample, which lead to optical absorption. Calculations show that simultaneous neutron and gamma irradiation does not significantly increase the optical absorption during the expected lifetime of the HiPER 4a facility. Under severe conditions (HiPER 4b), operation above 800 K or lens refreshing by thermal annealing treatments seem to assure adequate behavior.

Date Published: 18 February 2011
PDF: 12 pages
Proc. SPIE 7916, High Power Lasers for Fusion Research, 79160S (18 February 2011); doi: 10.1117/12.876163

Published in SPIE Proceedings Vol. 7916:
High Power Lasers for Fusion Research
Abdul A. S. Awwal; A. Mike Dunne; Hiroshi Azechi; Brian E. Kruschwitz, Editor(s)