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Exploration of possible improvements to the n-ToF diagnostics at the National Ignition Facility
Mahl, Adam Creveling
Mahl, Adam Creveling
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2017
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This M.S. thesis describes work related to a neutron time of flight (n-ToF) diagnostics at the National Ignition Facilitiy (NIF). The neutrons produced via deuterium-tritium (D-T) fusion reactions (14.1 MeV) in a laser imploded fuel capsule, emerge with an energy distribution reflecting both the fuel temperature and density. The density information is contained in the flux of “downscattered” neutrons (approximately 10-12 MeV) which arrive approximately 100 nsec after the main pulse at the n-ToF detectors' location. As the downscattered flux is much smaller (2-4 orders of magnitude, depending on shot conditions) than the 14.1 MeV flux, the information can be obscured in either (down) scattered neutron background at the detector location, or scintillation afterglow from the fast plastic (or liquid) scintillator detectors employed. This work uses simulation to explore the possibility of designing an advanced neutron beam collimator to reduce neutron scatter (2010-2011), as well as details an experiment performed at the Los Alamos Neutron Science Center (LANSCE) to explore if an optically filtered BaF2 crystal scintillator could become an alternative to the currently employed organic scintillators (2012).
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