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|Title:||Modelling and development of sub-nanosecond inertial fusion diagnostics|
|Authors:||Rubery, Michael Steven|
|Presented at:||University of Leicester|
|Abstract:||This thesis discusses the modelling and development of the Cherenkov detectors fielded at the National Ignition (NIF) and Omega facilities to measure observables important for improving understanding of inertial confinement fusion (ICF). It begins with an overview of ICF together with an introduction to the relevant laser facilities, theory and detectors. The Geometry and Tracking Version 4 (GEANT4), Monte Carlo Neutron Program (MCNP) and ACCEPT Monte Carlo codes were benchmarked and then validated experimentally at the high-intensity source facility using two Cherenkov detectors. GEANT4 was subsequently used for calculations of temporal response and light production from the Cherenkov detectors; thus allowing GRH's +-50 ps uncertainty to be achieved and improved measurements of the DT γ/n strength (4+-2 +-10-5) and DT γ spectral shape to be made. Building on this, the novel Prompt Areal Density Diagnostic (PADD1) was also designed to enable measurements of remaining shell at peak fusion reactivity. Limitations of the existing Cherenkov detectors are then introduced, specifically the photomultiplier tube (PMT) which limits bandwidth to 88 ps. Following an investigation into alternative technologies, Chemical Vapour Deposition (CVD) diamond emerged as a possible dynode candidate due to high secondary electron emission (> 20), significantly better than lead glass (1-3) used in micro-channel plate (MCP) PMTs. A CVD diamond transmission dynode < 100 nm thick could be incorporated into a PMT analogous to an MCP. Despite diamond's potential there are parameters, such as boron doping, surface termination and crystallinity which impact yield and require optimisation through experiment and simulation. A study of secondary electron modelling theory and limitations was thus performed, and an approach utilising an experimentally-derived dielectric function incorporated into the GEANT4 toolkit. This low-energy extension combined with measurements of diamond's emission characteristics will be used in the future to facilitate diamond's integration into a PMT.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Physics and Astronomy|
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