First measurements of the absolute neutron spectrum using the Magnetic Recoil Spectrometer (MRS) at OMEGA

Abstract

A new type of neutron spectrometer, called a Magnetic Recoil Spectrometer (MRS) has been built and activated at OMEGA, and currently being developed at the National Ignition Facility (NIF), for measurements of the absolute neutron spectrum in the range 6 to 30 MeV, from which ρR, Ti and yield can be determined. From the down-scattered neutrons in the range 6–10 MeV, a ρR can be inferred. From the tertiary spectrum (≫20 MeV), a second determination of the ρR can be inferred for high-yield implosions, which can be compared directly to the down-scattered neutron inferred ρR. Having such self-consistency check could prove immensely important for NIF fizzles that are on the threshold to ignite. In addition, absolute yield and a highly resolved 14-MeV primary neutron spectrum can be measured. This allows for measurements of Ti and, possibly more interestingly, non-thermal features, deviations from a single temperature and the effect of alpha-particle heating that might give an insight into the nature of a failed ignition-capsule implosions. In this talk, the results from the first measurements of the absolute spectrum of the down-scattered and primary neutrons at OMEGA will be presented. In addition, as much of the R&D and instrument optimization of the MRS at OMEGA is directly applicable to the MRS at the NIF, a description of the MRS design and characterization on the NIF is discussed as well.