Experimental Investigation of the Thermal Upset and Recovery of the National Ignition Facility's Optics Module
The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is being constructed as the latest in a series of high-power laser facilities to study inertial confinement fusion. In particular, the NIF will generate and amplify 192 laser beams and focus them onto a fusion fuel capsule the size of a BB. The energy deposited by the laser beams will raise the core temperature of the target to 100,OOO,OOO C, which will ignite the fusion fuel and produce a fusion energy output that is several times greater than the energy input. The ability to generate, condition, and focus 192 laser beams onto a target the size of a BB, requires precision optical hardware and instrumentation. One of the most critical pieces of optical hardware within the NIF is the Optics Module (OM), a mechanical apparatus which is responsible for optical focusing and frequency conversion of the laser beam to optimize the energy deposition at the fusion target. The OM contains two potassium dihydrogen phosphate (KDP), frequency conversion crystals and a focusing lens. The functionality of the KDP crystals is extremely temperature sensitive. Small temperature changes on the order of 0.1 C can significantly alter the performance of these components. Consequently, to maximize NIF system availability and minimize beam conditioning problems, accurate temperature control of the OM optical components was deemed a necessity. In this study, an experimental OM prototype, containing mock frequency conversion crystals and a focusing lens, was used determine the thermal stability provided by a prototype water temperature control system. More importantly, the OM prototype was used to identify and characterize potential thermal upsets and corresponding recovery times of the KDP crystals. The results of this study indicate that the water temperature control system is adequate in maintaining uniform steady-state temperatures within the OM. Vacuum pump-down and venting of the OM generated significant temperature changes in the optical components. However, the corresponding recovery times of the optical components were found to be less than three hours, well within the seven hour limit posed by NW operations. Simulated laser shots also were found to create thermal upsets within the OM's optical components over a range of heat deposition rates. However, the recovery times of these thermal upsets were found to be less than one hour. Finally, the use of non-contact infrared thermocouples was demonstrated as an effective means to track the temperature of the OM's optics.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 9456
- Report Number(s):
- LA-13609-MS; TRN: US0103129
- Resource Relation:
- Other Information: PBD: 1 May 1999
- Country of Publication:
- United States
- Language:
- English
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