NIF’s front end consists of three individually tunable oscillators that are mapped to different cones. Inner 23.5o quads receive one wavelength, the 30o quads receive the second wavelength, and all outer cone (44.5o and 50o) quads receive the third wavelength. 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.
The user requests a Dl 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 Dl 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 CMT) by the user.
Table 4-2. Current wavelength tuning ranges for the three oscillators on NIF.