A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
Browse
20 results
Search Results
Item MEASURING AND MODELING ELECTROMAGNETIC FORCES THAT INFLUENCE GRANULAR BEHAVIOR(2024) Pett, Charles Thomas; Hartzell, Christine M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)On the surfaces of small, airless planetary bodies, forces other than gravity, such as cohesive, magnetic and electrostatic forces, may dominate the behavior of regolith. Yet, the magnitude of these forces remains uncertain, as well as the link between grain-scale and bulk-scale physics. In this work, techniques for measuring and modeling electromagnetic forces that influence granular behavior are developed. We discuss an experimental method for measuring interparticle cohesion by breaking cohesive bonds between grains with electrostatic forces. The centroid positions of the lofted grains at the moment of detachment are imaged in order to numerically calculate initial accelerations to solve for cohesion. We propose the design of a payload that would be deployed on the Moon or an asteroid and use an electrically biased plate to induce electrostatic dust lofting and measure interparticle cohesion in situ. We would call the system \textbf{Small--FORCES} because it would be able to image \textbf{Small} \textbf{F}orces \textbf{O}ptically \textbf{R}esolved for \textbf{C}ohesion \textbf{E}stimation via \textbf{E}lectrostatic \textbf{S}eparation. We numerically integrate Poisson's equation and develop a model for the potential distribution of a photoelectron sheath as a function of distance from surfaces. We use this model to gauge the extent to which the solar wind will perturb the Small-FORCES electric field that is used to loft charged regolith inside the sheath and obtain suitable trajectories for imaging lofted regolith that will be used to measure cohesion. We then derive a formula to quantify the maximum region of our system's electric field that we predict can be shielded from the ambient solar wind, which depends on system dimensions and applied voltage. In another experiment, we investigated the affect of magnetic cohesion on the avalanching behavior of magnetic grains. We will introduce an instrument and novel method for characterizing the bulk magnetic susceptibility of granular mixtures by submerging an inductor coil in a bed of metallic beads. In prior works, the magnetic force on grains was calculated based on the magnetic susceptibility of a single grain, but our coil uniquely quantifies effects from void spaces and demagnetization in the bulk. Compared to both a commercial Terraplus Inc. KT-10 meter and theoretical approximations, we report similar trends in susceptibility values measured as a function of mass of ferromagnetic material per volume. We conclude the talk with a discussion on a conductive model we developed to simulate surfaces other than dielectrics in the solar wind. We use a 2D grid-free treecode to enable complex surface geometries that would be computationally intensive for traditional PIC codes. Instead of using the capacitance matrix method to calculate the induced surface charge magnitudes, we discretized the conductor surface into point charges and allow them to have Coulomb interactions with the external plasma particles. The linear system used to explicitly solve for the induced surface charge magnitudes couples the interaction between surface charges and plasma particles self-consistently via the conductive boundary condition. The model has been validated thus far with image charge theory.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 LOW TEMPERATURE PLASMA-METAL INTERACTIONS: PLASMA-CATALYSIS AND ELECTRON BEAM-INDUCED METAL ETCHING(2024) Li, Yudong; Oehrlein, Gottlieb G; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Low-temperature plasma can generate different types of chemically reactive species at gas temperatures far below what is required to form such species from thermal excitation. Interactions between these reactive plasma-generated species and material surfaces have great potential for various applications, such as semiconductor etching or gas conversion. Synergistic effects, where the production rate with two inputs is greater than the sum of the consequences of each individually, have been demonstrated by combining the plasma with other energy inputs such as heat or kinetic energy from ions or electrons. Understanding the mechanisms by which these species interact with relevant surfaces is vital for the future development of plasma processing, chemistry and physics. In this work, we focus on the interaction of long-lived plasma species, particularly neutrals, with metal. A remote plasma-surface configuration was applied, where the plasma itself does not directly contact the surface. Two examples of plasma-metal interactions will be discussed, one taking place at atmospheric and the other at low pressure. The first case is plasma-assisted catalytic oxidation of methane (CH4) using a nickel (Ni) catalyst at atmospheric pressure, implemented by combining a remote plasma jet. The interrelation of real-time measurements of reaction products and surface adsorbates and plasma diagnostics allowed the identification of atomic oxygen as the key plasma-generated species that drives the synergistic plasma-catalytic reaction. The in-situ characterizations of the surface and gas phase reactions reveal the possible key reaction pathways for the plasma-catalysis reactions. We also observed the activation of the catalyst resulting from long-lasting catalyst surface modification induced by plasma species interaction. The second case is the damage-free etching of refractory metals, ruthenium (Ru) and tantalum (Ta), at low pressure. This was implemented by combining a remote plasma source (RPS) with an electron beam (EB) source. We investigated the effects of CF4 and Cl2 additions to Ar/O2 RPS effluents and we find that Ar/O2 with Cl2 addition induces the highest Ru etch rate (ER) and best removal selectivity over Ta. The surface chemistry characterization by spatially-resolved XPS reveals the possible mechanism of the electrons and neutrals induced materials etching. We also proposed a model that considers the fundamental aspects of the etching reaction and successfully predicts the major features of the electron and neutral induced etching reactions.Item PLASMA-BASED ATOMIC SCALE ETCHING APPROACHES USING EITHER ION OR ELECTRON BEAM ACTIVATION(2022) Lin, Kang-Yi; Oehrlein, Gottlieb; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma dry etching has been extensively employed in semiconductor manufacturing processes for anisotropic pattern transfer. With device miniaturization, the conventional approach utilizing continuous wave plasma etching does not meet the requirement for sub-nanometer processing nodes, including profile control and atomic-scale etching selectivity. Additionally, the direct plasma exposure of a substrate raises the concern of plasma damage and undesired material removal. We describe improvements of plasma-based etching techniques and identified novel ways for enabling material removal. We have systematically studied different precursor chemistries for atomic layer etching on etching selectivity of SiO2 to Si3N4 and SiO2 to Si and obtained an understanding of the surface chemistry evolution. Compared to the conventional approach that mixes fluorocarbon and hydrogen precursors, selected hydrofluorocarbon can deliver optimal plasma chemistry that produces a reduced F/C film in the deposition step and realizes atomic-scale etching selectivity. We also report a new approach for establishing etching selectivity of HfO2 over Si by integrating substrate-selective deposition into an atomic layer etching sequence. The optimal precursor chemistry can selectively deposit on the Si surface as a passivation layer and convert HfO2 to metal-organic compounds for desorption. Finally, we designed and built a system that consists of an electron flood gun and a remote plasma source to demonstrate the concept of a new etching approach by exploiting electron-neutral synergistic effects. This configuration achieves precisely controlled SiO2 or Si3N4 etching by co-introducing an electron beam and Ar/CF4/O2 remote plasma. This approach also addresses the issue of limited precursor chemistries in electron beam-induced etching.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 Effects of Water Plasma Chemistry on Helicon Thruster Performance(2019) Petro, Elaine Marie; Sedwick, Raymond J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The focus of this work is on the operation of a helicon thruster with water as the propellant. The characteristics of a water plasma are investigated and used to develop an analytical thrust efficiency model for the system. The efficiency of a helicon thruster operating with water vapor is compared to the efficiency with traditional noble gas propellants. Next, the predicted efficiency range is compared with other state-of-the-art electric propulsion devices. The addition of an ‘electrodeless’ ion cyclotron heating stage is investigated as a means of increasing thrust efficiency. The thrust efficiency model is extended to assess the parameter space for which the addition of ion cyclotron heating improves performance. Additionally, a particle-based trajectory model is developed to study antenna sizing, phasing effects, and energy conversion. Finally, the effects of second-order reactions on plasma composition and acceleration efficiency are explored using particle balance and particle-in-cell methods.Item Plasma-Surface Interaction at Atmospheric Pressure: from Mechanisms with Model Polymers to Applications for Sterilization(2018) Luan, Pingshan; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cold temperature atmospheric pressure plasma (APP) produces many types of chemically reactive species and is capable of modifying materials at atmospheric pressure. Studying plasma-surface interaction (PSI) at such pressure has been challenging due to the small mean-free-path (< 100 nm) which prohibits the conventional method of using independently controlled beams of ions/neutrals to isolate the role of each species. In this dissertation, we developed an alternative approach of studying PSI at atmospheric pressure using well-controlled source-ambient-sample systems and comprehensive surface/gas phase characterization techniques. In this new approach, we emphasize the controlled generation of reactive species from the plasma source, the regulated transportation of reactive species to the target surfaces, as well as the simplified material structure subjected to plasma treatment. To isolate and identify the role of certain reactive species on materials, a plasma source is selected with its operating conditions carefully tuned for the delivery of such species to target surface. Plasma-induced effects on model polymers and biomolecules were characterized and then quantitatively correlated to the gas phase species. Due to the multi-phase nature of PSI, many characterization techniques, including that of plasma/gas phases such as optical emission spectroscopy (OES), Fourier transform infrared spectroscopy (FTIR) and UV absorption, and that of material surfaces such as X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR) FTIR and Ellipsometry were adopted. Using this approach, we were able to evaluate the effect of both short- and long-lived reactive neutrals on many types of surface moieties. For example, we find that atomic O and OH radicals are able to cause fast material removal but moderate oxidation on the etched surface. We also find that O3 can participate in the chemical modification of aromatic rings, i.e. cleavage and their conversion into ether, ester carbonyls and surface organic nitrate groups, both on surface and in the polymer bulk. We also find evidence for (1) the competition between etching and surface modification processes when a high density of short-lived reactive species is involved, and (2) three polymer transformation stages when large fluxes of long-lived reactive species are interacting with styrene-based polymers. Lastly, we extended our work to explore the potential application of APP reactors for disinfecting raw foods and evaluated bacterial inactivation mechanisms.Item COLD ATMOSPHERIC PRESSURE PLASMA SURFACE INTERACTIONS WITH POLYMER AND CATALYST MATERIALS(2018) Knoll, Andrew Jay; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cold atmospheric pressure plasma (CAP) is an excellent source of reactive species because they are able to produce these species cheaply, in a variety of configurations, and in a way that can be distributed easily but there needs to be more understanding of how they specifically interact with surfaces. The goals of this dissertation are to understand what the critical reactive species reaching a surface are for particular applications. As a first step we find that a plasma in direct electrical contact with a polymer material shows high etching rate and non-uniform treatment whereas a remote regime treatment can lead to a relatively uniform treatment over the exposed to plasma area. The interaction of vacuum ultraviolet (VUV) light with polymer surfaces was found to be critical under conditions where local oxygen is displaced by noble gas flow. This VUV flux is also dependent on plasma source type, being highest for high voltage sources using noble gas flow. For a surface microdischarge (SMD) source we find high activation energy compared with atomic oxygen etching suggesting less reactive species reaching the surface are causing surface modification. However, for an atmospheric pressure plasma jet (APPJ) source we find that the activation energy changes over treatment distance, decreasing below the value expected for atomic oxygen as the jet gets closer to the surface. Additionally we find evidence of directional etching for the close distances which becomes less directional for further distance treatments suggesting we have a contribution from high energy species at closer distances despite there being no visible contact between the plasma plume and the polymer surface. Nickel catalyst materials interacting with plasma can be enhanced to show increased breakdown of methane and production of different product species such as CO compared to just the catalyst. This catalyst material also shows carbon deposition by CO and COO- groups by plasma treatment, though increased plasma power and temperature can then remove these groups as well.Item Simulation and Optimization of the Continuous Electrode Inertial Electrostatic Confinement Fusor(2017) Chap, Andrew Mark; Sedwick, Raymond J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A concept for generating nuclear fusion power and converting the kinetic energy of aneutronic fusion products into electric energy is proposed, and simulations are developed to design and evaluate this concept. The presented concept is a spherical fusor consisting of linear ion acceleration channels that intersect in the sphere center, where the converging ions form a high-energy, high-density fusion core. The geometry is that of a truncated icosahedron, with each face corresponding to one end of an ion beam channel. Walls between the channels span radially from the outer fusion fuel ionization source to an inner radius delimiting the fusion core region. Voltage control is imposed along these walls to accelerate and focus the recirculating ions. The net acceleration on each side of the channel is in the direction of the center, so that the ions recirculate along the channel paths. Permanent magnets with radial polarization inside the walls help to further constrain the ion beams while also magnetizing electrons for the purpose of neutralizing the fusion core region. The natural modulation of the ion beams along with a proposed phase-locked active voltage control results in the coalescence of the ions into ``bunches'', and thus the device operates in a pulsed mode. The use of proton-boron-11 (p-11B) fuel is studied due to its terrestrial abundance and the high portion of its energy output that is in the form of charged particles. The direct energy converter section envelopes the entire fusion device, so that each fusion fuel channel extends outward into a fusion product deceleration region. Because the fusion device operates in a pulsed mode, the fusion products will enter the energy conversion region in a pulsed manner, which is ideal for deceleration using a standing-wave direct energy converter. The charged fusion products pass through a series of mostly-transparent electrodes that are connected to one another in an oscillating circuit, timed so that the charged fusion products continuously experience an electric field opposite to the direction of their velocity. In this way the kinetic energy of the fusion products is transferred into the resonant circuit, which may then be connected to a resistive load to provide alternating-current energy at the frequency of the pulsed ion beams. Preliminary calculations show that a one-meter fusor of the proposed design would not be able to achieve the density required for a competitive power output due to limits imposed by Coulomb collisions and space charge. Scaling laws suggest that a smaller fusor could circumvent these limitations and achieve a reasonable power output per unit volume. However, ion loss mechanisms, though mitigated by fusor design, scale unfavorably with decreasing size. Therefore, highly effective methods for mitigation of ion losses are necessary. This research seeks to evaluate the effectiveness of the proposed methods through simulation and optimization. A two-dimensional axisymmetric particle-in-cell ion-only simulation was developed and parallelized for execution on a graphics processing unit. With fast computation times, this simulation serves as a test bed for investigating long-timescale thermalization effects as well as providing a performance output as a cost function for optimization of the electrode positions and voltage control. An N-body ion-only simulation was developed for a fully 3D investigation of the ion dynamics in an purely electrostatic device. This simulation uses the individual time-step method, borrowed from astrophysical simulations, to accurately model close encounters between particles by slowing down the time-step only for those particles undergoing sudden high acceleration. A two-dimensional hybrid simulation that treats electrons as a fluid and ions as particles was developed to investigate the effect of ions on an electrostatically and magnetically confined electron population. Electrons are solved for at each time-step using a steady-state iterative solver. A one-dimensional semi-analytic simulation of the direct energy conversion section was developed to optimize electrode spacing to maximize energy conversion efficiency. A two-dimensional axisymmetric particle-in-cell simulation coupled with a resonant circuit simulation was developed for modeling the direct energy conversion of fusion products into electric energy. In addition to the aforementioned simulations, a significant contribution of this thesis is the creation of a new model for simulating Coulomb collisions in a non-thermal plasma that is necessary to account for both the low-angle scattering that leads to thermalization as well as high-angle scattering that leads to ion departure from beam paths, and includes the continuous transition between these two scattering modes. The current implementation has proven problematic with regard to achieving sufficiently high core densities for fusion power generation. Major modifications of the current approach to address the space charge issues, both with regard to the electron core population and the ion population outside of the core would be necessary.Item PARTICLE CHARGING EFFECTS ON PIV MEASUREMENTS OF PLASMA ACTUATORS(2017) Masati, Arber; Sedwick, Raymond; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma actuators gained popularity during the change of the millennium for their ability to induce airflow and reattach stalled flow. Since then, investigations have been conducted to characterize their performance and extend their applications. Plasma actuators can be used to increase lift, decrease drag, and increase the efficiency of wind turbines. Phase locked ensemble averaging particle image velocimetry (PIV) is used to determine the induced velocity field and characterize actuator behavior and performance. However, very few studies account for particle charging from dusty plasma theory. Particle charging theories for high pressure plasmas predict a mostly linear trend between charge and particle size, with smaller particles charging less. In this work, PIV experiments were conducted with monodisperse nanoparticles for sizes ranging between 300 nm and 1250 nm. Results showed that smaller particles follow the flow more closely. PIV uncertainty quantification was performed for ensemble averaging processing. A weighted linear fit was applied to each vector and extrapolated to the 0 nm particle speed, which is taken as the true air speed. Stokes drag force fields were calculated using the known velocity difference, and using a force balance calculation the electrostatic force acting on the particles was calculated. The electrostatic force near the actuator electrode was always acting upstream, implying that particles can attain either negative or positive charge, depending on the phase.