The NIF laser is routinely operated at or slightly above the damage threshold limits in order to extract the maximum performance. This operating mode often results in damage to the FOA optics, which are exposed to the highest powers and fluences. We manage and mitigate the optical damage in multiple steps. The FOA optics on all 192 beams are inspected after high fluence shots using FODI. If a damage site is detected on an optical component, it is logged and included in the performance model for the laser. It is also monitored with subsequent FODI inspections for growth. The growth of a damage site is arrested by blocking a small amount of the beam (~2 cm diameter disc) centered on the damage site location using the PSS on NIF. The number of such blocked sites is limited to such that the energy loss is less than 5% per beam. Periodically, we exchange the damaged FOA components (crystals, WFLs, and grating debris shields) with fresh ones. The optical damage sites are mitigated in an offline facility and the mitigated optics are placed back into service (recycled) by installing them on NIF beamlines. We also continue to develop processes that produce more damage-resistant optics so they can be in the beamline for a larger number of shots.
A damage risk assessment is calculated for each proposed experiment on NIF. The sequencing of experiments is arranged such that the damage to the optics and growth rate of damaged sites from the shots is optimally matched to the damage mitigation and refurbishment rate. Current mitigation and recycling facility capacity is able to support over 400 experiments per year on NIF.
