Physics & Astronomy ETDs

Publication Date

Spring 5-15-2020

Abstract

High energy density (HED) systems are some of the most extreme environments ever created by mankind. Systems with pressures greater than 1 MBar can only be created by a handful of devices on earth, often utilizing high intensity lasers or pulsed power machines. HED systems offer a view into an extreme form of matter only seen in stellar cores, supernovas and other powerful astrophysical systems. Creating HED systems on Earth offer the possibility, if the physics and technology can be matured, to one day create a fusion power plant. If a system is hot and dense enough, the fusion reaction can drive more fusion reactions through the alpha particle depositing its energy. There has been a generation goal of getting this fusion chain reaction to create high yield and gain, however, this regime, called ignition, has remained elusive. Diagnosing HED systems to understand the degradation preventing ignition presents a challenge. HED pockets are often short lived (nanoseconds or picoseconds) and concurrent with a release of a physical blast shock, nuclear particles, a strong electromagnetic pulse and a noisy radiation environment. Cherenkov detectors to measure energy thresholded, time resolved gamma rays is one such technique that can be applied to these systems to gain insight and understanding to the properties of HED systems. In this dissertation, the fundamentals and background of this diagnostic technique are applied in detail to three HED systems. Gas Cherenkov detectors are applied onto the National Ignition Facility's inertial confinement fusion ignition campaigns. Inertial confinement fusion uses high powered lasers to compress a capsule full of deuterium-tritium fuel surrounding by a carbon ablator shell, which is used to push the fuel into high densities and temperatures. A technique to isolate a 4.4 MeV carbon gamma ray is introduced and applied to understand the areal density and compression of the outside portion of the inertial confinement fusion pusher. The new data reveals that the outside portion of the pusher followed the expected hydrodynamic predicted trends, while the inner fuel portion of the pusher looks to be degraded and less compressible. This data suggests for specific degradation mechanisms acting on the capsule that preferentially degrade the fuel, such as ablator-ice mix. The time resolution of the gamma detector also gives information about the velocity of the carbon ablator during the fusion burn. Second, gamma ray measure mix studied field on the OMEGA laser system are shared, showing a complicated mix landscape for spherical implosions. Aerogel Cherenkov detectors are fielded on the Mercury pulsed power facility at the Naval Research Lab which creates an accelerated electron beam to create a strong bremsstrahlung x-ray source. The Aerogel Cherenkov detectors are able to characterize and measure time resolved signals of the x-ray pulse, vital information for the x-ray pulse to be feed into a radiography or photofission source. This dissertation presents a body of work that applies a diagnostic technique to an extreme experimental conditions, receives novel measurements and interprets their results.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Mark Gilmore

Second Committee Member

Hans Herrmann

Third Committee Member

Edl Schamiloglu

Fourth Committee Member

Yongho Kim

Fifth Committee Member

Douglas Fields

Language

English

Keywords

nuclear detectors, Cherenkov detectors, inertial confinement fusion, gamma ray detectors, national ignition facility

Document Type

Dissertation

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