The neutron time-of-flight (NTOF) detectors at the National Ignition Facility (NIF) make the highest resolution measurement of the neutron energy spectrum from NIF implosions. This spectral information provides insight into the fuel assembly at bang time of the implosion. The workhorse detectors are a suite of three detectors that are fielded at ~20m from the target. These detectors have been used since late 2012 to measure traditional fusion variables such as neutron yield, ion temperature and fuel areal density. The high quality, high signal-to-background data of the newly-implemented detectors have enabled measurement of portions of the neutron spectrum that were previously challenging or impossible; remaining ablator areal density, D(n,n) and T(n,n) backscatter edges, hot spot velocity, and high-energy reaction-in-flight neutrons are measured routinely. Thermal components of the spectrum (=100keV) have yet to be measured due to the lack of sensitivity of the detectors to those neutrons, but we plan to field a low energy neutron spectrometer to facilitate these measurements. The low energy portion of the neutron spectrum will be critical in understanding cross section measurements in a NIF target capsule.

Neutron spectrometry using neutron time-of-flight detectors at the National Ignition Facility

248th National Meeting (2014)

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