Development and use of advanced nuclear diagnostics and neural networks to diagnose 3D morphology and power balance in inertial fusion implosions at OMEGA and NIF

Abstract

Inertial confinement fusion (ICF) is one of several ways to perform nuclear fusion in the laboratory, and is thus appealing as a potential future energy source. Achieving high gain at ICF facilities like the National Ignition Facility (NIF) and OMEGA requires new ways of measuring implosion conditions such as the shape of the shell at minimum-volume and the power balance in the hot-spot. This dissertation describes several novel instruments and analysis techniques to measure these. First is a method to combine information from existing diagnostics that probe asymmetries, such as the neutron imaging system, the real-time neutron activation detectors, and the neutron time-of-flight spectrometers. Our technique uses a forward-fit to a simplified physics model to produce a single self-consistent 3D picture of the implosion. Markov chain Monte Carlo is used to provide robust uncertainty quantification. Second is a knock-on deuteron imager to measure deuterons elastically scattered out of the shell by fusion neutrons. This diagnostic would enable a full 3D reconstruction of both the hot-spot and shell geometry. Analysis procedures were developed for this diagnostic, and commissioning experiments were carried out to validate the procedures and associated hardware, providing improved capabilities for imaging OMEGA implosions. Third is a time-resolved neutron spectrometer called MRSt which would record a time-resolved neutron spectrum. Extensive modelling of the MRSt’s response and analysis procedures has been carried out, with which it has been predicted that the system as designed will meet the top-level physics requirements needed for novel insights. A path forward for implementing this spectrometer has been identified. These projects represent significant advancements in our abilities to diagnose ICF implosions, which will improve our understanding of degradations and failure modes in ICF implosions and lead to higher gain overall. This will hopefully one day enable nuclear fusion energy as a clean energy source.