Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Signal Processing and Forward Modeling of Space Debris Detection via Plasma Solitons(2024) DesJardin, Ian; Hartzell, Christine M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The nonlinear interaction of objects in low Earth orbit with the space plasma environment has been hypothesized to cause precursor soliton plasma waves. These plasma-object interactions may lead to unique engineering applications, especially the detection of hazardous sub-centimeter orbital debris that is undetectable by conventional methods. This nonlinear perturbation is currently modeled by the forced Korteweg - de Vries (fKdV) equation. This thesis aims to understand and characterize these waves through simulation beyond the fKdV model while progressing space-based and ground detection schemes. Ultimately this technique may play an important role in the problem of detecting small space debris. Three aspects of this detection scheme are developed. This includes two unconventional methods of detecting solitons. First the inverse scattering transform (IST), a mathematical spectral technique for decomposing a time series, is shown to automatically detect solitons from data. A numerical experiment using the fKdV model is performed to demonstrate this ability. The IST is suitable as an in situ detection method. It could be the basis of a debris collision early warning system for spacecraft. Second, the existing technique of ionospheric sensing using Global Navigation Satellite System (GNSS) is extended to detecting spacecraft plasma wakes. Traditionally, it is used for global scale space weather monitoring. An experiment is carried out using a known target, the International Space Station, on existing GNSS receivers that measure the ionospheric irregularity associated with the spacecraft. This experiment shows that there is a modification to the total electron content (TEC) when the ISS flies through the radio line-of-sight. Using models that are compared to the experiment, a multi-point sensor is proposed that would resolve the diffraction pattern from these plasma structures. This work uses multi-fluid plasma simulation to refine the fKdV model of soliton generation from debris. In particular, we find that the range of ion acoustic Mach numbers that are conducive to precursor soliton generation is larger than predicted by the fKdV equation. A new theory that matches the multi-fluid simulation results is derived using pressure balances to predict the supercritical Mach number. This new theoretical understanding of the critical Mach numbers predicts a wider range of orbits that will create precursor solitons than in previous studies. In addition, several new details of precursor solitons are discovered and characterized with multi-fluid simulation. This includes changes in the amplitude scaling of the periodicity of soliton generation (the "intersoliton interval"). Importantly, corrections to the first order results of the fKdV equation which couple fluid velocity, density, and electrostatic potential are identified. A theory that explains this in the small amplitude limit is derived. For debris detection, this effect impacts how the soliton is detected. The same soliton will manifest different amplitudes in each plasma species, contrary to the result of the fKdV equation. Thus, a model error in inferring debris properties from solitons has been discovered.Item AN INVESTIGATION OF THE OBSERVABILITY OF PLASMA SOLITONS GENERATED BY CUBESATS USING INCOHERENT SCATTER RADAR ARRAYS(2023) Wilson, Connor MacNaughton; Hartzell, Christine M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Conventional ground-based observation methods, such as tracking radars, are unable to reliably detect and track subcentimeter orbital debris. This debris poses a risk to crewed and robotic spacecraft as it is capable of penetrating structures and damaging instruments. Tracking this debris reliably would allow for improved mitigation maneuvers to reduce mission risk. Based on recent publications, an alternate detection method could involve sensing plasma density solitary waves. These waves, henceforth “solitons,” are predicted to be produced by the interaction of the electrical charge on the lethal nontrackable debris with the local ionospheric plasma. This body of work seeks to test the feasibility of detecting the predicted soliton generated by defunct 1U CubeSats because they are already tracked using conventional methods and are predicted to produce solitons. Ground-based observers, such as incoherent scatter radars operated by the European Incoherent Scatter Scientific Association, may be able to detect the presence of solitons created by a CubeSat traveling through the ionosphere. This may be accomplished by observing the variation in electron density of the measurements near the time when the CubeSat passes through the radar beam. Testing this hypothesis initially involves several 1U CubeSats that are propagated from their last time of observation until they overfly an incoherent scatter radar site during its operating cycle. In this observation window, the hypothesized soliton is modeled for each target of opportunity. The modeled solitons will travel with the CubeSats and are effectively pinned to them. These pinned solitons are compared with electron density measurements from the radar station. The variance in the measurements makes it unlikely to confirm an observation without a filter, but the apparently uncorrelated variance of the plasma density measurements is on the same order of magnitude as the one-dimensional soliton disturbances induced by the CubeSat. Based on this, a one-dimensional linear Kalman filter is implemented to look for positively correlated deviations of the electron density estimates when the debris is passing through the radar beam; three out of the five test targets are positively correlated and a fourth is nearly correlated. Simulating the pinned solitons across a variation of times and altitudes indicates that there are better times of day and year to look for evidence of these solitons; the largest possible soliton for this data set is 140% the magnitude of the mean electron density. Further analysis of this best case scenario determines that it is unlikely any measurements could detect a deviation in electron density due to a soliton because of the size of the range gate and beam width relative to the signal size and strength. The range gate and beam width would need to be on the order of 1 meter as opposed to the 700 meter range gate in the test case. The sample rate would need to be less than 10 µs instead of 1 minute. Given this conclusion, the experimental evidence implies that there may be another factor causing the correlation algorithm to function as initially intended; perhaps the soliton is larger than predicted or the CubeSat itself is being detected in the measurement.Item ON THEORETICAL ANALYSES OF QUANTUM SYSTEMS: PHYSICS AND MACHINE LEARNING(2022) Guo, Shangjie; Spielman, Ian B; Taylor, Jacob M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Engineered quantum systems can help us learn more about fundamental physics topics and quantum technologies with real-world applications. However, building them could involve several challenging tasks, such as designing more noise-resistant quantum components in confined space, manipulating continuously-measured quantum systems without destroying coherence, and extracting information about quantum phenomena using machine learning (ML) tools. In this dissertation, we present three examples from the three aspects of studying the dynamics and characteristics of various quantum systems. First, we examine a circuit quantum acoustodynamic system consisting of a superconducting qubit, an acoustical waveguide, and a transducer that nonlocally couples both. As the sound signals travel $10^5$ times slower than the light and the coupler dimension extends beyond a few phonon emission wavelengths, we can model the system as a non-Markovian giant atom. With an explicit result, we show that a giant atom can exhibit suppressed relaxation within a free space and an effective vacuum coupling emerges between the qubit excitation and a confined acoustical wave packet. Second, we study closed-loop controls for open quantum systems using weakly-monitored Bose-Einstein condensates (BECs) as a platform. We formulate an analytical model to describe the dynamics of backaction-limited weak measurements and temporal-spatially resolved feedback imprinting. Furthermore, we design a backaction-heating-prevention feedback protocol that stabilizes the system in quasi-equilibrium. With these results, we introduce closed-loop control as a powerful instrument for engineering open quantum systems. At last, we establish an automated framework consisting of ML and physics-informed models for solitonic feature identification from experimental BEC image data. We develop classification and object detection algorithms based on convolutional neural networks. Our framework eliminates human inspections and enables studying soliton dynamics from numerous images. Moreover, we publish a labeled dataset of soliton images and an open-source Python package for implementing our framework.Item Study of Soliton Space Charge Waves in Intense Electron Beams(2013) Mo, Yichao; O'Shea, Patrick G; Kishek, Rami A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High brightness electron beams have wide applications in accelerator-driven light sources, X-ray, free-electron lasers (FELs), spallation neutron sources and intense proton drivers. Advanced accelerators demand superior beam quality for such intense beams, where the non-linear space charge force will introduce collective effects and limit the maximum beam current and quality. Near the cathode, all beams of interest begin as space-charge dominated beams. Density fluctuations can naturally occur and lead to space charge waves. Therefore, it is crucial to understand and control how these beam modulations develop in an intense beam. This dissertation addresses the longitudinal beam dynamics of large-amplitude perturbations on electron beams. I report on the first systematic characterization of solitons in electron beams. Solitons are localized persistent waves that behave like particles, preserving their properties (shape, velocity, etc.) over long distances and through collisions with other solitons. They have practical applications and are of interest to many disciplines such as condensed matter physics, plasma physics, beam physics, optics, biology and medicine. Whereas solitons in electron beams have been predicted on theoretical grounds decades ago in the form of longitudinal space charge waves, they were never experimentally observed until recently in the University of Maryland Electron Ring (UMER). By introducing a pulsed laser beam on a thermionic cathode, an electron beam with a narrow density perturbation from photoemission is generated. The perturbation then evolves into longitudinal space charge waves that propagate along the beam. For large-amplitude initial perturbations, a soliton wave train is observed. The soliton's properties are confirmed experimentally. The results are compared with cold fluid model in theory and the WARP particle-in-cell (PIC) code in simulation. Reasonable agreement is achieved. This reproducible nonlinear process provides an alternative for a tunable, coherent radiation sources without wigglers/undulators. The soliton pulse spacing is therefore investigated, which is found dependent on the pipe radius (g-factor) and beam plasma frequency.