Abstract
The gamma reaction history (GRH) diagnostic is a multichannel, time-resolved, energy-thresholded gamma-ray spectrometer that provides a high-bandwidth, direct-measurement of fusion reaction history in inertial confinement fusion implosion experiments. 16.75 MeV deuterium+tritium (DT) fusion gamma-rays, with a branching ratio of the order of 10(-5)gamma/(14 MeV n), are detected to determine fundamental burn parameters, such as nuclear bang time and burn width, critical to achieving ignition at the National Ignition Facility. During the tritium/hydrogen/deuterium ignition tuning campaign, an additional gamma-ray line at 19.8 MeV, produced by hydrogen+tritium fusion with a branching ratio of unity, will increase the available gamma-ray signal and may allow measurement of reacting fuel composition or ion temperature. Ablator areal density measurements with the GRH are also made possible by detection of 4.43 MeV gamma-rays produced by inelastic scatter of DT fusion neutrons on C-12 nuclei in the ablating plastic capsule material. (C) 2010 American Institute of Physics. [doi:10.1063/1.3495770]