NIF’s front end consists of four individually tunable oscillators that are mapped to different cones. Each of the inner 23.5º, 30º, 44.5º, and 50º quads receive independent wavelengths, with a total of four potentially different wavelengths. The installation of the three oscillators and the specific mapping of their wavelengths to the inner and outer cones is driven by the need to control and mitigate the laser-plasma instabilities in the ignition hohlraums.2 Figures 4-6 and 4-7 show the ranges of wavelengths available and their locations used.
The user requests a Δλ wavelength separation between the inner and outer cones of beams that is required to meet the physics goals of the experiment. The potential backscatter risk due to laser–plasma interactions is reviewed by the backscatter working group, and if the request is safe for the facility, it is accepted for the shot. The absolute wavelengths consistent with the approved Δλ are then determined by the facility in order to minimize the overall number of changes and impact to the schedule. These final wavelengths are then configured in the shot setup (i.e., in SST) by the user.
2P. Michel et al., “A three wavelength scheme to optimize hohlraum coupling on the National Ignition Facility,” Physical Review E 83 046409 (2011), available at: https://ereports-ext.llnl.gov/pdf/460646.pdf.
