<p> High-energy electron beams, with electron kinetic energies (&sim;1 MeV) much greater than the surrounding plasma temperature (&lt;1 keV), are a common feature in Z-pinch pulsed power experiments. Their existence is indicated by non-thermal spectral signatures, such as high-energy Bremsstrahlung photons from the anode hardware and characteristic X-ray emission not representative of the pinch "hot-spot" temperatures. Despite their regular occurrence, the properties of these beams (kinetic energy, current) are not well known.</p><p> This dissertation describes an experimental study of X-pinch generated high-intensity electron beams, performed on the 1 MA pulsed power generator at the Nevada Terawatt Facility, and the feasibility of a novel method for inferring the total kinetic energy in the beam, through time-resolved measurements of the beam-induced shock that propagates through the anode.</p>

<p> Ionizing radiation poses a significant challenge for human and robotic space missions. Practical luminescent sensors will depend heavily upon research investigating the resistance of these materials to ionizing radiation and the ability to anneal or self-heal the damage caused by such radiation. In 1951, Birks and Black experimentally showed that the luminescent efficiency of anthracene bombarded by alpha particles varies with total fluence. From 1990 to the present, we found that the Birks and Black relation describes the reduction in light emission yield for every tested luminescent material except lead phosphate glass due to proton irradiation. These results indicate that radiation produced quenching centers compete with emission for absorbed energy. The purpose of this thesis is to present new results from related luminescent materials by exposing them to a 1-3 MeV proton beam. Particular emphasis will be placed on recent measurements made with bright luminescent materials, such as zinc sulfide doped with manganese (ZnS:Mn), europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA), an magnesium tetrakis dibenzoylmethide triethylammonium (MgD4TEA). This research can be used to help determine if luminescent materials can be used as a real-time sensor to detect ionizing radiation.</p>

<p> Neutrons produced deuterium Z-pinch plasmas are widely acknowledged to be a consequence of highly accelerated deuterons undergoing nuclear fusion with relatively stationary deuterons. The acceleration is thought to occur in intense fields created in the MHD instabilities that punctuate the plasma column. Interestingly, the energies of the accelerated ions exceed the applied voltage across the electrode gap. We use the 1 MA Zebra pulsed-power generator at the Nevada Terawatt Facility (NTF) to explore this poorly understood fast neutron production mechanism by creating deuterium Z-pinches in three distinct types of target loads. The loads are a cylindrical shell of deuterium gas, the far less explored deuterided palladium wire arrays, and a deuterium-carbon ablated laser plume target, which is unique to the NTF. </p><p> The pinch dynamics vary considerably in these three targets and provide the opportunity to explore the ion acceleration mechanism. We infer the characteristics of the accelerating fields from a wide range of diagnostic data including the neutron yield, energy spectrum and angular distribution, and the properties of the matching electron beams that are accelerated in the same field, and the energetic X-rays they produce on stopping. The plasma and the instabilities were recorded on several high-speed imaging diagnostics along with time-integrated soft (&lt;10 keV) X-ray pinhole images. The three load types produced total neutron yields in the 10⁸&ndash;10¹⁰ n/pulse range. The synchronization we observe between the ion and electron beams and the development of instabilities leads us to conrm the acceleration hypothesis. We also present the characteristics of the fields and ion beams in these varied pinches.</p>

This dissertation presents experiments that studied two gravity driven granular channel flows. The first experiment used magnetic resonance imaging to measure the density and displacement distributions of poppy seeds flowing in a rough walled channel. Time-averaged measurements of normalized velocity and density showed little flow speed dependence. Instantaneous measurements, however, showed marked velocity dependence in the displacement distributions. There was evidence of aperiodic starting and stopping at lower flow speeds and the onset of density waves on a continuous flow at higher speeds. The second experiment measured forces in all three spatial directions at the boundary of a flow of steel balls. The relationship between the normal and the tangential forces were examined statistically and compared to the Coulomb friction model. For both large and small forces, the tangential and normal forces are unrelated, as there appears to be a strong tendency for the tangential force to maintain a value that will bear the weight the weight of the particles in flow.

The means by which magnetic reconnection in Earth's space environment is observed is limited by current instrument technology and timing of satellite orbits. Imaging capabilities from a spacecraft platform are still developing, and in-situ measurements are confined to the spacecraft's orbit. The goal of this dissertation is to provide and apply methods by which the spatial extent of magnetic reconnection at Earth's magnetopause can be quantified. An accepted single value, or range of spatial extents of magnetopause reconnection has eluded the scientific community for over half a century. This dissertation provides two methods by which the spatial extent can be sampled. First, with the development of a CubeSat, the Cusp Plasma Imaging Detector (CuPID). CuPID is built with a wide field-of-view soft X-ray telescope to image the photons resulting from solar wind charge exchange between atmospheric neutrals and high charge-state solar wind ions. During magnetic reconnection at the magnetopause, solar wind ions are routed along field lines to Earth's cusps in the polar regions. In the magnetospheric cusps, these solar wind ions can penetrate deeper into Earth's neutral atmosphere, producing an observable signal for a low Earth orbiting satellite. The design of the CuPID mission and the calibrations of CuPID's instruments are presented. CuPID was launched in September 2021, but did not respond to commanding from the ground. Efforts to modify and improve the ground station led to the discovery of a probable root cause of failure with CuPID's flight radio. A second method of observing magnetic reconnection utilizes in-situ measurements of plasma populations and magnetic fields. The THEMIS mission, orbiting five satellites continuously since 2007, traverse the magnetopause nearly every orbit when their orbital apogee is on the dayside. When two spacecraft cross the magnetopause simultaneously and both observe features of magnetic reconnection, the spatial extent of reconnection is constrained by their spacing. Using statistics from 174 events of spacecraft conjunctions at the magnetopause, the spatial extent of reconnection as observed by THEMIS is on average 3,148 km. This study also investigates the processes by which magnetic reconnection is constrained, including plasma beta gradient drifts and position on the magnetopause flanks.

In this research we study the mixing of viscous fluids in a model flow, the eccentric cylinder system. The flow between eccentric rotating cylinders is used because an analytic expression for the stream function exists and we have fabricated an apparatus to experimentally generate the flow. We use the flow to determine the extent to which several computational methods are able to predict the experimental mixing in the flow. We have found that Poincare sections give a good indication of the maximum extent of mixing in the experiments but they give no information on the rate of mixing. The locations of elliptic periodic points give an indication of where 'islands' of regular behavior will occur in the flow. The manifolds of the hyperbolic periodic point with the largest eigenvalue give a template of the striation pattern which forms in the experiments. Finally, stretching plots appear to match the experiments quite well. We have found that co-rotation of the cylinders leads to mixing over a larger region of the flow domain than the equivalent counter-rotating motion of the cylinders. Driving the cylinders with different waveforms appears to produce little or no difference in the mixing. The Melnikov method has been adapted to adjust the waveforms such that the resultant mixing is in even closer agreement. In addition, we have determined that the points which stretch the most start on the stable manifold of a hyperbolic periodic point and end up on the unstable manifold. This results in the stretching plots assuming the shape of the manifolds and consequently matching the striation patterns of the experiments. Finally, we have determined that the methods of analysis presented here can be applied to flows where only a discretized representation of the velocity field exists. This means that our methods of analysis will be effective even when the flow field must be determined numerically.

The equilibrium statistical behavior of phase flows on surfaces of complicated topology is studied. Both classical tools developed in the theory of Riemann surfaces and numerical methods associated with discrete mathematics (graph theory) are applied to the characterization of the equilibrium statistical behavior of systems with U(1) symmetry on two-dimensional manifolds. The relation between a surface's topology and physical parameters such as the superfluid density, vortex core shape and boundary effects is investigated. The effect of quantization is traced through the characterization of states via the Hodge decomposition and in the partition function. It is shown that for surfaces of an appropriate shape a new type of Kosterlitz-Thouless transition is possible. This situation is novel because quantized vortices are required only for ergodicity and the disordering of the superfluid/normal phase transition is by fluctuations in the nonsingular harmonic flows.

<p> Geometric integrators yield high-fidelity numerical results by retaining conservation laws in the time advance. A particularly powerful class of geometric integrators is symplectic integrators, which are widely used in orbital mechanics and accelerator physics. An important application presently lacking symplectic integrators is the guiding center motion of magnetized particles represented by non-canonical coordinates. Because guiding center trajectories are foundational to many simulations of magnetically confined plasmas, geometric guiding center algorithms have high potential for impact. The motivation is compounded by the need to simulate long-pulse fusion devices, including ITER, and opportunities in high performance computing, including the use of petascale resources and beyond. </p><p> This dissertation uses a systematic procedure for constructing geometric integrators &mdash; known as variational integration &mdash; to deliver new algorithms for guiding center trajectories and other plasma-relevant dynamical systems. These variational integrators are non-trivial because the Lagrangians of interest are degenerate - the Euler-Lagrange equations are first-order differential equations and the Legendre transform is not invertible. The first contribution of this dissertation is that variational integrators for degenerate Lagrangian systems are typically <i>multistep methods.</i> Multistep methods admit parasitic mode instabilities that can ruin the numerical results. These instabilities motivate the second major contribution: degenerate variational integrators. By replicating the degeneracy of the continuous system, degenerate variational integrators avoid parasitic mode instabilities. The new methods are therefore robust geometric integrators for degenerate Lagrangian systems. </p><p> These developments in variational integration theory culminate in one-step degenerate variational integrators for non-canonical magnetic field line flow and guiding center dynamics. The guiding center integrator assumes coordinates such that one component of the magnetic field is zero; it is shown how to construct such coordinates for nested magnetic surface configurations. Additionally, collisional drag effects are incorporated in the variational guiding center algorithm for the first time, allowing simulation of energetic particle thermalization. Advantages relative to existing canonical-symplectic and non-geometric algorithms are numerically demonstrated. All algorithms have been implemented as part of a modern, parallel, ODE-solving library, suitable for use in high-performance simulations.</p>

Because the universe is primarily composed of plasma, the interaction of plasmas and magnetic fields is of great importance for astrophysics. In this dissertation, we investigate three magnetic instabilities and examine their possible effects on astrophysical objects. First, we model solar coronal structures as Double Beltrami states, which are the lowest energy equilibria of Hall magnetohydrodynamics. We find that these states can undergo a catastrophe with characteristics similar to those of a solar eruption, such as a flare or coronal mass ejection. We then investigate magnetic reconnection and particle acceleration in moderately magnetized relativistic pair plasmas with three-dimensional particle-in-cell simulations of a kinetic-scale current sheet. We find that in three dimensions the tearing instability produces a network of interconnected and interacting magnetic flux ropes. In its nonlinear evolution, the current sheet evolves toward a three-dimensional, disordered state in which the resulting flux rope segments contain magnetic substructure on kinetic scales and sites of temporally and spatially intermittent dissipation. We find that reconnection produces significant particle acceleration, primarily due to the electric field in the X-line regions between flux ropes; the resulting particle energy spectrum can extend to high Lorentz factors. We find that the highest energy particles are moderately beamed within. / text

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