High-yield magnetic recoil neutron spectrometer on the National Ignition Facility for operation up to 60 MJ

Recent progress at the National Ignition Facility (NIF), with neutron yields of order 1 × 10^17, places new constraints on diagnostics used to characterize implosion performance. The Magnetic Recoil neutron Spectrometer (MRS), which is routinely used to measure yield, ion temperature (Tion), and down-scatter ratio (dsr), has been adapted to allow measurements of dsr up to 5 × 10^17, and yield and Tion up to 2 × 10^18 in the near term with new data processing techniques and conversion foil solutions. This paper presents a solution for extending MRS operation up to a yield of 2 × 10^19 (60 MJ) by moving the spectrometer outside of the NIF shield wall. This will not only enhance the upper yield limit by 10× but also improve signal-to-background by 5×.