Theses and Dissertations from UMD
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Item Characteristics of Plasma Solitons Produced by Small Orbital Debris(2020) Truitt, Alexis; Hartzell, Christine; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sub-centimeter orbital debris is currently undetectable using ground-based radar and optical methods. However, pits in Space Shuttle windows produced by paint chips demonstrate that small debris can cause serious damage to spacecraft. Recent analytical, computational and experimental work has shown that charged objects moving quickly through a plasma will cause the formation of plasma density solitary waves, or solitons. Due to their exposure to the solar wind plasma environment, even the smallest space debris will be charged. Depending on the debris size, charge and velocity, debris may produce plasma solitons that propagate along the debris velocity vector and could be detected with existing sensor technology. Plasma soliton detection would be the first collision-free method of mapping the small debris population. The first major contribution of this thesis is the identification of orbital locations where solitons will be produced, as a function of debris size and speed. Using the Chan & Kerkhoven pseudospectral method, we apply the Forced Korteweg-de Vries equation to describe the amplitude, width, and production frequency of solitons that may be produced by mm-cm scale orbital debris, as a function of the debris' size, velocity, and location (altitude, latitude, longitude) about Earth. Analytical solutions result in solitons that propagate forever without damping, assuming a uniform plasma environment. However, Earth's space plasma is complex, with processes that could cause the solitons to dampen. Damped solitons will have a limit to the distance they will travel before becoming undetectable. For our second major contribution, we calculated the propagation distance of solitons in the presence of damping processes. We applied the Damped Forced Korteweg-de Vries equation to calculate the damping rate of the solitons, and estimate the resulting soliton propagation distance. We demonstrate that Landau damping dominates over collisional damping for these solitons. It is necessary to understand the damping of solitons in order to assess the feasibility of on-orbit debris detection. In our first contribution, we demonstrate that one dimensional simulations are sufficient to model the orbital debris solitons that propagate along the debris velocity vector. However, in order to fully understand the soliton signatures in a 3D spatial environment, it is necessary to extend the Damped Forced Korteweg-de Vries model to three spatial dimensions. For our final major contribution, we apply the Damped Forced Kadomtsev-Petviashvili Equation, which is a natural extension for waves described by the Damped Forced Korteweg-de Vries equation. Transverse solitonic perturbations extend across the width of the debris, with predictable amplitudes and speeds that can be approximated by the one dimensional Damped Forced Korteweg-de Vries equation at the transverse soliton location. The transverse perturbations form soliton rings that advance ahead of the debris in the three dimensional simulations, allowing for additional opportunity for detection. With the current absence of a dedicated, calibrated, on-orbit debris detection sensor, plasma soliton detection would be the first collision-free method of mapping the small debris population. The characteristics of plasma solitons described here are necessary to evaluate the feasibility of orbital debris detection via soliton detection with future debris detection systems.Item Ionospheric Turbulence Near the Upper Hybrid Layer: Theory and Experiment(2016) Najmi, Amir Christopher; Papadopoulos, Konstantinos; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The thesis presents experimental results, simulations, and theory on turbulence excited in magnetized plasmas near the ionosphere’s upper hybrid layer. The results include: The first experimental observations of super small striations (SSS) excited by the High-Frequency Auroral Research Project (HAARP) The first detection of high-frequency (HF) waves from the HAARP transmitter over a distance of 16x10^3 km The first simulations indicating that upper hybrid (UH) turbulence excites electron Bernstein waves associated with all nearby gyroharmonics Simulation results that indicate that the resulting bulk electron heating near the upper hybrid (UH) resonance is caused primarily by electron Bernstein waves parametrically excited near the first gyroharmonic. On the experimental side we present two sets of experiments performed at the HAARP heating facility in Alaska. In the first set of experiments, we present the first detection of super-small (cm scale) striations (SSS) at the HAARP facility. We detected density structures smaller than 30 cm for the first time through a combination of satellite and ground based measurements. In the second set of experiments, we present the results of a novel diagnostic implemented by the Ukrainian Antarctic Station (UAS) in Verdansky. The technique allowed the detection of the HAARP signal at a distance of nearly 16 Mm, and established that the HAARP signal was injected into the ionospheric waveguide by direct scattering off of dekameter-scale density structures induced by the heater. On the theoretical side, we present results of Vlasov simulations near the upper hybrid layer. These results are consistent with the bulk heating required by previous work on the theory of the formation of descending artificial ionospheric layers (DIALs), and with the new observations of DIALs at HAARP’s upgraded effective radiated power (ERP). The simulations that frequency sweeps, and demonstrate that the heating changes from a bulk heating between gyroharmonics, to a tail acceleration as the pump frequency is swept through the fourth gyroharmonic. These simulations are in good agreement with experiments. We also incorporate test particle simulations that isolate the effects of specific wave modes on heating, and we find important contributions from both electron Bernstein waves and upper hybrid waves, the former of which have not yet been detected by experiments, and have not been previously explored as a driver of heating. In presenting these results, we analyzed data from HAARP diagnostics and assisted in planning the second round of experiments. We integrated the data into a picture of experiments that demonstrated the detection of SSS, hysteresis effects in simulated electromagnetic emission (SEE) features, and the direct scattering of the HF pump into the ionospheric waveguide. We performed simulations and analyzed simulation data to build the understanding of collisionless heating near the upper hybrid layer, and we used these simulations to show that bulk electron heating at the upper hybrid layer is possible, which is required by current theories of DAIL formation. We wrote a test particle simulation to isolate the effects of electron Bernstein waves and upper hybrid layers on collisionless heating, and integrated this code to work with both the output of Vlasov simulations and the input for simulations of DAIL formation.Item 3D Ionospheric Effects on HF Propagation and Heating(2015) Zawdie, Katherine A.; Papadopoulos, Konstantinos; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The thesis uses a three-dimensional, first-principles model of the ionosphere in combination with High Frequency (HF) raytracing model to address key topics related to the physics of HF propagation and artificial ionospheric heating. In particular: 1. Explores the effect of the ubiquitous electron density gradients caused by Medium Scale Traveling Ionospheric Disturbances (MSTIDs) on high-angle of incidence HF radio wave propagation. Previous studies neglected the all-important presence of horizontal gradients in both the cross- and down-range directions, which refract the HF waves, significantly changing their path through the ionosphere. The physics-based ionosphere model SAMI3/ESF is used to generate a self-consistently evolving MSTID that allows for the examination of the spatio-temporal progression of the HF radio waves in the ionosphere. 2. Tests the potential and determines engineering requirements for ground- based high power HF heaters to trigger and control the evolution of Equatorial Spread F (ESF). Interference from ESF on radio wave propagation through the ionosphere remains a critical issue on HF systems reliability. Artificial HF heating has been shown to create plasma density cavities in the ionosphere similar to those that may trigger ESF bubbles. The work explores whether HF heating may trigger or control ESF bubbles. 3. Uses the combined ionosphere and HF raytracing models to create the first self-consistent HF Heating model. This model is utilized to simulate results from an Arecibo experiment and to provide understanding of the physical mechanism behind observed phenomena. The insights gained provide engineering guidance for new artificial heaters that are being built for use in low to middle latitude regions. In accomplishing the above topics: (i) I generated a model MSTID using the SAMI3/ESF code, and used a raytrace model to examine the effects of the MSTID gradients on radio wave propagation observables; (ii) I implemented a three- dimensional HF heating model in SAMI3/ESF and used the model to determine whether HF heating could artificially generate an ESF bubble; (iii) I created the first self-consistent model for artificial HF heating using the SAMI3/ESF ionosphere model and the MoJo raytrace model and ran a series of simulations that successfully modeled the results of early artificial heating experiments at Arecibo.Item Neutral Gas and Plasma Interactions in the Polar Cusp(2012) Olson, David K.; Moore, Thomas E.; Coplan, Michael A.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)When the solar wind interacts with the Earth's magnetosphere, both energy and matter can be transferred across the magnetopause boundary. This transfer gives rise to numerous phenomena, including ion outflow and neutral upwelling in the polar cusps. These processes are caused by a transfer of energy to the ionospheric plasma and neutral gas through various mechanisms. The heated plasma or gas expands, increasing the density of the atmosphere at high altitudes by as much as a factor of two, and injecting ionospheric plasma into and even outside of the magnetosphere. These two phenomena are examined in two ways: A novel high energy (0.1--10 keV) spectrograph for ionospheric cusp ions was designed as part of the Rocket Experiment for Neutral Upwelling (RENU), a sounding rocket campaign carried out at the northern polar cusp to observe the electrodynamic properties of the cusp during a neutral upwelling event. This instrument is called the KeV Ion Magnetic Spectrograph (KIMS). Ion outflow in the ionosphere has shown evidence of correlation with both Poynting flux and soft electron precipitation in the cusp. The heat input from these energy sources might also affect neutral gas in the ionosphere, contributing to upwelling phenomena seen at the dayside cusp. Using data from the Fast Auroral Snapshot Explorer (FAST) and the Challenging Minisatellite Payload (CHAMP) satellites, correlations of electromagnetic and particle energy inputs are examined with both ion outflow and neutral upwelling in the cusp. The added ability to process large quantities of data quickly and reference the data between separate satellites in this statistical survey gives clues to the consistency of the observed correlations with ion outflow over time and to the relative importance of these energy sources in the neutral upwelling phenomenon. It also provides the ability to understand these connections in a broad spectrum of conditions of the Sun and solar wind as well as in the Earth's magnetosphere.