Browsing by Author "Yost, Dylan, committee member"
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Item Open Access Development of a methane cavity ring-down spectrometer for deployment on ground and aerial based vehicles(Colorado State University. Libraries, 2020) Martinez, Benjamin, Jr., author; Yalin, Azer P., advisor; Yost, Dylan, committee member; Windom, Bret, committee memberRecent findings show that the oil and natural gas industry is responsible for a large portion of total anthropogenic methane (CH4) emissions. These findings have driven the need for suitable methane detection and quantification methods. Methane emissions on the scale that the oil and gas industry produce (13 Tg[CH4]/year) can cause environmental effects comparable to that of CO2 due to methane's high global warming potential. The present thesis focuses on continued developments and improvements to a laser-based methane sensor that uses the open-path cavity ring-down spectroscopy (CRDS) technique. The sensor is intended for continuous mobile monitoring of methane emissions from the oil and gas industry by deployment on ground and aerial based vehicles. Sensor performance in a range of environmental conditions is characterized and shows the feasibility of deploying the sensor in real world applications. Indoor accuracy tests were done utilizing a closed-path system and verified through comparison with a commercial analyzer. Sensor measurements compared to the commercial analyzer showed good 1:1 agreement. Allan variance studies within laboratory measurements demonstrated the sensor's high sensitivity of ~10 ppb. A heater system was designed and implemented for overall improvement in low temperature conditions. The heater system successfully improved the thermal range of the sensor to temperatures as low as 0°C. Environmental tests also showed the sensor's reliability in harsh winter conditions over a ~70-day period of continuous measurement. The sensor's methane plume detection ability and sensitivity in simulated controlled releases through vehicle deployment is demonstrated and good 1:1 agreement was found comparing against a commercial analyzer in the field. Controlled release experiments demonstrated CH4 measurements more than 400 meters away from the source at an emission rate of 0.5 g[CH4]/s. A retro-fitted closed-path cell was constructed and tested in field campaigns to reduce noise due to Mie scattering. Additional field testing with simulated controlled releases were performed to test a modified, light-weight (4.1 kg) sensor mounted on two unmanned aerial vehicle platforms. Detection of various plumes in the UAV configuration was shown to be feasible with the current mounting method. Sensitivity in UAV flights were as low as 17 ppb which demonstrated the robust opto-mechanical capabilities of the sensor.Item Open Access Diagnostics and characterization of direct injection of liquified petroleum gas for development of spray models at engine-like conditions(Colorado State University. Libraries, 2023) Sharma, Manav, author; Windom, Bret, advisor; Yalin, Azer, committee member; Yost, Dylan, committee memberResearch within the realm of internal combustion (IC) engines is concentrated on enhancing fuel efficiency and curbing tailpipe emissions, particularly CO2 and regulated pollutants. Promising solutions encompass the utilization of direct injection (DI) and alternative fuels, with liquefied petroleum gas (LPG) standing out as a notable candidate. LPG presents a pragmatic and economical option for fueling the heavy-duty transportation sector in the United States. However, widespread adoption hinges on achieving energy conversion efficiencies in LPG engines comparable to those in diesel engine platforms. The overarching goal of this research is to address fundamental limitations to achieving or surpassing near-diesel efficiencies in heavy-duty on-road liquefied petroleum gas engines. Owing to substantial differences in physical properties compared to traditional fuels, an enhanced understanding and modeling of LPG sprays become imperative. This work conducts an experimental and numerical analysis of direct-injected propane and iso-octane, serving as surrogates for LPG and gasoline, respectively, under diverse engine-like conditions. The overall objective is to establish a baseline for the fuel delivery system required in future high-efficiency DI-LPG heavy-duty engines. Propane, emulating LPG, undergoes injection across various engine-like conditions, encompassing early and late injections, as well as boosted engines, using a range of direct injectors available in both research and commercial domains. Optical diagnostics, including high-speed schlieren and planar Mie scattering imaging, were performed to study the spray penetration, liquid and vapor phase regions, and mixing of propane and to characterize bulk and the plume-specific spray behavior of propane. The study also investigates the influence of injector geometry on spray performance. Iso-octane was used as a surrogate for gasoline, and propane was used to compare LPG's behavior with more conventional DI fuel. The experimental results and high-fidelity internal nozzle-flow simulations were then used to define best practices in computational fluid dynamics (CFD) Lagrangian spray models. Optical imaging revealed that, unlike iso-octane, propane's spray propagation was fed by its flash boiling, spray collapse, and a high degree of vaporization, resulting in a direct proportionality of propane's penetration length to temperature. These unique attributes categorize propane as an unconventional spray, necessitating corrections to injection and breakup models to replicate under-expanded jet dynamics and emulate flash boiling-driven spray development across various research and commercial injectors.Item Embargo Molecular dynamics simulation studies and experimental measurements of radiofrequency heating for strongly coupled and extremely magnetized ultracold neutral plasmas(Colorado State University. Libraries, 2023) Jiang, Puchang, author; Roberts, Jacob L., advisor; Yost, Dylan, committee member; Lee, Siu Au, committee member; Yalin, Azer, committee memberUltracold neutral plasmas(UNPs) are good experimental platforms for fundamental plasma physics studies because of their experimentally adjustable parameters, accessible timescales, ability to enter the strong coupling parameter regime, and easy access to large degrees of electron magnetization. The work in this thesis contains both simulation and experimental studies of UNPs. One simulation project describes a new UNP heating mechanism discovered using Molecular Dynamics simulations: DC electric field heating. This DC electric field heating mechanism occurs when a DC electric field is present when the plasma is formed. sets a lower limit of how cold UNP electron temperatures can be reached experimentally. A second simulation project investigates a many-body physics effect on collisional damping in UNPs and a breakdown in standard plasma theory treatments when the plasma is approaching the strongly coupled regime. This breakdown arises due to the increasing significance of three- or many-body electron-ion interactions influencing the plasma transport properties and particle collisions. My simulations find evidence for this being the case. Experimental studies of UNP electron-ion collision physics during the application of high-frequency RF electric fields to the UNP were conducted, and measurements of the RF-induced electron heating rate from the weak magnetized regime to extremely magnetized regime were performed. The results obtained are in qualitative agreement with the theory prediction but there's quantitative disagreement. Possibilities for resolving this disagreement are presented.Item Open Access Near-resonant and resonant light in ultracold gases(Colorado State University. Libraries, 2020) Gilbert, Jonathan, author; Roberts, Jacob, advisor; Yost, Dylan, committee member; Bradley, Mark, committee member; Marconi, Mario, committee memberThis dissertation describes experiments and calculations involving light manipulation of atoms and light propagation in ultracold gases. There are three major sections to this dissertation. Each section presents a research topic connected to the main subject of near-resonant and resonant light in ultracold gases. First, this dissertation details the theoretical description and experimental implementation of a novel cooling technique for ultracold atoms trapped in a confining potential. Manipulating the internal states of atoms by applying near-resonant laser pulses at specified times leads to high energy atoms being preferentially selected and then slowed to achieve cooling. We call the technique "spatially truncated optical pumping (STOP) cooling." Advantages of the technique include its straightforward adaptability into experiments already using a magneto-optical trap; its applicability to any species that can be laser cooled and trapped in a confining potential; it does not depend on highly specific transitions for cooling; it does not depend on number loss for cooling. We present experimental results from applying the technique to an ultracold gas of 87Rb. We also present theoretical predictions of expected cooling rates, along with possible improvements to our apparatus that could lead to further cooling. Next, this dissertation details numerical calculations of near-resonant light propagation through a highly absorptive elongated ultracold gas. The confined gas modeled by these calculations are representative of gases commonly found in ultracold atom experiments. The spatial density distribution and spatial extent of these gases leads to a substantial gradient in the index of refraction. In addition, these gases can have a smaller spatial extent than that of the cross section of a laser beam that illuminates them. We present calculations that show the index variation in these systems can lead to frequency-dependent focusing or defocusing of incident near-resonant light. In some cases, focusing results in light intensities inside of the gas that are over an order of magnitude higher than the incident value. Additionally, we show that refraction and diffraction of the light results in non-intuitive patterns forming in the directions perpendicular to the light propagation. Lastly, this dissertation details the theoretical treatment and experimental measurements of the time-dependent absorption and phase response of an ultracold gas that is suddenly illuminated by near-resonant light. These studies focus on dynamics occurring over timescales on the order of an atomic excited state lifetime. Because the atoms cannot respond instantaneously to the applied light, both the absorption response and phase response require time to develop, with the phase response being slower than the absorption response. Related polarization effects such as Faraday rotation are due to phase shifts imparted by the gas, and therefore these effects also require time to develop. We detail our experimental measurements of the time-dependent development of Faraday rotation in an ultracold gas of 85Rb and compare the results to predictions using a theoretical approach based on solving optical Bloch equations. We identify how parameters such as the applied magnetic field strength and optical thickness of the gas influence the response timescales of the gas.Item Open Access Precision measurements on a single trapped beryllium ion(Colorado State University. Libraries, 2024) Fairbank, David M., author; Brewer, Samuel M., advisor; Yost, Dylan, committee member; Sanner, Christian, committee member; Van Orden, Alan, committee memberPrecision laser spectroscopy of transitions in simple atoms can be used as a stringent test of many-body quantum electrodynamics (QED) calculations, or to extract subtle information about internal nuclear structure. 9Be+ is a three electron ion which has been the focus of study in ion trap and high energy beam experiments dating back several decades. We present the first measurements of the D-lines in 9Be+ using a single trapped ion, which reduced the experimental uncertainty of both the D1 and D2 transitions by an order of magnitude. A framework for characterization of systematic shifts due to effects like photon recoil and quantum interference in ion trap-based measurements of strong transitions is presented. From the D2 lineshape data, a 2P excited state lifetime was extracted with reduced uncertainty and better agreement with theory, compared to previous work. The first experimental measurement of the unresolved 2P3/2 hyperfine splittings is reported, which helped to uncover a sign error in the theoretical prediction of the 2P3/2 electric quadrupole hyperfine constant. This measurement required development of techniques to selectively isolate and measure the unresolved components, utilizing the exceptional state preparation and control available for trapped ions. The 1.25 GHz 2S1/2 ground state hyperfine splitting was measured with a relative uncertainty of 1.6×10−11 using microwave Ramsey spectroscopy and is in good agreement with previous measurements made in Penning traps at NIST. The technique can be extended to the rare isotope 7Be+, for which the current hyperfine constant uncertainty is four orders of magnitude larger. This planned measurement could enable extraction of an improved value of the 7Be nuclear Zemach radius. D-line measurements on the rare isotopes 7,10Be+ are also planned using the techniques developed for 9Be+. A comparison of the fine structure splitting across the isotope chain can be used to extract the relative nuclear charge radii or test the many-body QED contributions to theory in Li-like ions. A new ion trap was built and direct ablation loading of the ion trap from small 9BeCl2 salt deposits was demonstrated in preparation for loading the rare isotopes from evaporated aqueous solution.Item Open Access Two-photon absorption laser induced fluorescence (TALIF) of neutral xenon in a Hall Effect thruster plasma(Colorado State University. Libraries, 2021) Wegner, James Thaddeus, author; Yalin, Azer P., advisor; Williams, John, committee member; Yost, Dylan, committee memberThis work presents measurements of ground state neutral xenon in the plume of a 1.5 kW Hall Effect thruster (HET) using two-photon absorption laser induced fluorescence (TALIF). Neutral xenon particles in the thruster plasma play an important role in ionization processes, overall energy conversion, and life-limiting interactions with surrounding wall materials in the thruster. Therefore, a detailed understanding of the neutral particle dynamics within the plume is desired. The TALIF diagnostic technique allows for laser induced excitation of xenon from its ground state using commercially available laser systems at accessible ultraviolet wavelengths (~222 nm). The signal collected from fluorescence of the excited atoms can be used to determine the local neutral density. We present a demonstration of TALIF first in a barium oxide (BaO) hollow cathode plume at varying radial positions, then in an HET plume at varying axial positions using fiber coupled collection optics with a spatial resolution of 3.14 mm2. The detection limit of the TALIF measurement system 2.1 cm downstream of the thruster face was estimated to be 8 x 1017 m-3 as determined by comparison to a known reference signal. The ability to analyze ionization and thermal characteristics using these results is also discussed.