Nuclear Fusion Reaction Kinetics and Ignition Processes in Z Pinches

This thesis presents work on two topics related to nuclear fusion in plasmas. The first topic is the energy spectrum of products of fusion reactions in plasmas, called the production spectrum. The second is an investigation of the fusion reaction processes in high energy density Z pinch plasmas and the feasibility of ignition of such plasmas. A method is presented for the derivation of production spectra for plasmas with various distributions of ion velocities. The method is exact, requiring the solution of a 5 dimensional integral and is suitable for both isotropic and anisotropic distributions. It is shown that many of the integrals can be solved analytically. The solutions are used to study the spectra of neutron energies produced by deuterium-deuterium and deuterium-tritium reactions. It is found that for maxwellian distributions of ions the neutron spectrum is asymmetric with a longer high energy tail when compared with gaussian approximations of the spectrum. Deuterium and deuterium-tritium Z pinch plasmas are studied computationally using a hybrid code in which the fuel is modelled as a magnetohydrodynamic (MHD) fluid and fast ions are modelled as discrete particle-in-cell (PIC) particles. Using a Z pinch model in which the magnetic and thermal pressures are in equilibrium it is found that significant energy gain can be achieved for currents greater than 50MA. Deuterium gas puff experiments with a 15MA current are also analysed computationally in order to determine the reaction mechanism. The results of MHD simulations in 3 dimensions are post-processed with a PIC code to model reactions occurring due to the acceleration of deuterium ions by large electric fields. It is found that reactions due to this beam-target mechanism represent a small fraction (0.0001) of the number of thermonuclear reactions

Back-traced Garbage Collection

This disclosure describes back-traced garbage collection in a computer. A back-traced garbage collector searches backwards from an object in an object graph, until a root node is encountered, or until there are no further objects to search. If a root node is not encountered, the searched objects are unreachable and are deleted. The garbage collector can run incrementally, process portions of the object graph, and determine reachability of individual objects without examining the entire object graph. The garbage collector has low latency. The garbage collector is tunable, for example, in response to program characteristics and performance requirements

Rotating Leaks in the Stadium Billiard

The open stadium billiard has a survival probability, $P(t)$, that depends on the rate of escape of particles through the leak. It is known that the decay of $P(t)$ is exponential early in time while for long times the decay follows a power law. In this work we investigate an open stadium billiard in which the leak is free to rotate around the boundary of the stadium at a constant velocity, $\omega$. It is found that $P(t)$ is very sensitive to $\omega$. For certain $\omega$ values $P(t)$ is purely exponential while for other values the power law behaviour at long times persists. We identify three ranges of $\omega$ values corresponding to three different responses of $P(t)$. It is shown that these variations in $P(t)$ are due to the interaction of the moving leak with Marginally Unstable Periodic Orbits (MUPOs)

The effects of magnetic field topology on secondary neutron spectra in magnetized liner inertial fusion

The Magnetized Liner Inertial Fusion (MagLIF) concept involves the compression of a magnetized fuel such that the stagnated fuel contains a magnetic field that can suppress heat flow losses and confine α particles. Magnetic confinement of α particles reduces the fuel ρR required for ignition. Recent work [1,2] has demonstrated that the magnitude of the magnetic field in deuterium fuel can be inferred from the yields and spectra of secondary DT neutrons. In this work we investigate the potential for using the shape of the secondary neutron spectra to diagnose the magnetic field topology in the stagnated fuel. Three different field topologies that could possibly occur in MagLIF experiments are studied: (1) a cylindrical fuel column containing axial and azimuthal magnetic field components, (2) a fuel column which is pinched at the ends to form a magnetic mirror and (3) a fuel column that has a helical tube shape with magnetic field lines following the helical path of the tube’s axis. Each topology is motivated by observations from experimental or simulated MagLIF data. For each topology we use a multi-physics model to investigate the shapes of the secondary neutron spectra emitted from a steady-state stagnated fuel column. It is found that the azimuthal and helical topologies are more suitable than the mirror topology for reproducing an asymmetry in the axial spectra that was observed in experiments. Gorgon MHD simulations of the MagLIF implosion in 1D are also carried out. These show that sufficient azimuthal magnetic field can penetrate from the liner into the fuel to qualitatively reproduce the observed spectral asymmetry

High performance extendable instruction set computing

In this paper, a new architecture called the extendable instruction set computer (EISC) is introduced that addresses the issues of memory size and performance in embedded microprocessor systems. The architecture exhibits an efficient fixed length 16-bit instruction set with short length offset and immediate operands. The offset and immediate operands can be extended to 32 bits via the operation of an extension flag. The code density of the EISC instruction set and its memory transfer erformance is shown to be significantly higher than current architectures making it a suitable candidate for the next generation of embedded computer systems. The compact EISC instruction set introduces data dependencies that seemingly limit deep pipeline and superscalar implementations. This paper suggests a mechanism by which these dependencies might be removed in hardware

Rotating nuclei at extreme conditions: Cranked Relativistic Mean Field Description

The cranked relativistic mean field (CRMF) theory is applied for the description of superdeformed (SD) rotational bands observed in $^{153}$Ho. The question of the structure of the so-called SD band in $^{154}$Er is also addressed and a brief overview of applications of CRMF theory to the description of rotating nuclei at extreme conditions is presented.Comment: 4 pages, 1 PostScript figure, LaTex, uses 'espcrc1.sty', to be published in Proceedings of International Nuclear Physics Conference, Paris, 1998 which will appear in Nuclear Physic

CCTV as a crime prevention strategy: a review of the literature

CCTV is undoubtedly one of the most renowned weapons in the fight against crime. Funded by Allianz Ireland, Cork Chamber of Commerce and the Faculty of Law, University College, Cork, this research sought to examine the emergence of CCTV as a crime prevention strategy and the effectiveness it displays in this role. To do this, a literature review was undertaken to uncover the theoretical rationale underpinning the use of CCTV and explore the rise of surveillance as mechanism of social control. Numerous evaluations and studies, particularly from Britain, but also Ireland, were reviewed to investigate the impact of CCTV on crime, to assess the nature and value of those evaluations and consequently, to formulate a number of recommendations. It is hoped that this work will prove useful to those contemplating the future deployment of CCTV as a crime prevention strategy.CCJHR Research Projects, Centre for Criminal Justice & Human Rights (CCJHR), School of Law, University College Cor

Improving lives of children through occupational therapy vision evaluation and intervention

INTRODUCTION: Children in inpatient settings are in an unfamiliar environment that does not facilitate engagement in typical occupations. Children report multiple concerns with the hospital environment and experience including physical pain, loss of independence, loss of meaningful activities, lack of routine, and loss of control. Occupational therapists play a distinct role in improving the hospitalization experience for children by addressing these concerns. By improving the evaluation and treatment of visual deficits for children in inpatients settings, occupational therapists can increase children’s function and independence in meaningful activities and maximize psychological well-being. THEORETICAL PERSPECTIVE AND EVIDENCE: Self-determination theory posits that humans have three innate psychological needs – competence, autonomy, and relatedness. These needs are not being met for children in inpatient settings as shown by multiple qualitative studies, however occupational therapy can aid in meeting these needs through proper intervention. DESCRIPTION OF PROJECT: Resources were developed to improve the evaluation and treatment of visual deficits in children in inpatient settings including a vision screening tool, treatment protocol, referral protocol, and functional implications of visual deficits chart. METHODS: The vision screening tool and protocols were used on a small sample of patients (n=6) to identify and treat visual deficits. A survey was provided to occupational therapists to determine feasibility, usefulness, and effectiveness of the resources. CONCLUSION: The resources are useful and feasible for evaluating and treating visual deficits in children in the inpatient setting