Browsing by Author "Yalin, Azer P., advisor"
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Item Open Access A direct-reading particle sizer (DRPS) with elemental composition analysis(Colorado State University. Libraries, 2023) Sipich, James Robert, author; Yalin, Azer P., advisor; Volckens, John, committee member; L'Orange, Christian, committee member; Carter, Ellison, committee memberThere is a lack of aerosol measurement technology capable of quantifying, in real-time, the size, concentration, and composition of large inhalable particles with an aerodynamic diameter larger than 20 µm. Aerosols of this size penetrate the upper respiratory system upon inhalation and present surface contamination hazards upon settling. The ability to obtain information on the composition of airborne particles is necessary to identify and control risks from exposure to potentially toxic materials, especially in the workplace. The objective of this work was to validate the performance of a prototype Direct-Reading Particle Sizer (DRPS) that counts and sizes particles via time-of-flight light scattering and determines single-particle elemental composition via Laser-Induced Breakdown Spectroscopy (LIBS). Counting, sizing, and spectral measurement efficiency were evaluated using test aerosols of multiple materials with diameters between 25 and 125 µm. Particle sizing results showed good agreement with optical microscopy images. The relationship between the median aerodynamic diameters measured by the DRPS time-of-flight and optical microscopy was linear (Deming regression slope of 0.998) and strongly correlated (r2 > 0.999). The mean absolute difference between the median aerodynamic diameters measured by the instrument by time-of-flight and microscopy over all 8 test aerosol types was 0.9 µm with a mean difference in interquartile range of 1.9 µm. The prototype sensor uses an optical triggering system and pulsed Nd:YAG laser to generate a microplasma and ablate falling particles. Particle composition is determined based on collected emission spectra using a real-time material classification algorithm. The accuracy of the composition determinations was validated with a set of 1480 experimental spectra from four different aerosol test materials. We have studied the effects of varying detection thresholds and find operating conditions with good agreement to truth values (F1 score ≥ 0.9). Details of the analysis method, including subtracting the spectral contribution from the air plasma, are discussed. The time-of-flight aerodynamic diameter measurement and LIBS elemental analysis capabilities demonstrated by the DRPS provide a system capable of both counting, sizing, and identifying the composition of large inhalable particles.Item Open Access Cavity enhanced instruments for detection of hydrogen chloride and aerosol optical extinction(Colorado State University. Libraries, 2013) Franka, Isaiah S., author; Yalin, Azer P., advisor; Kreidenweis, Sonia M., committee member; Marchese, Anthony J., committee memberThis thesis concerns the development of cavity enhanced instruments for atmospheric science studies. Hydrochloric acid (HCl) is an important reservoir species for active halogens which are thought to participate in cycles that deplete ozone. In order to understand these halogens and their effect on ozone depletion, a cavity ring-down spectroscopy (CRDS) based instrument was developed for ultra-sensitive HCl concentration measurements. The instrument has a (1σ) limit of detection of 10 pptv in 5 min and has high specificity to HCl. Aerosols are a fundamental contribution to Earth's radiation budget and represent one of the largest unconstrained unknowns in estimating climate change. The effect of aerosols on climate and air quality is closely tied to their spectral properties as well as particle chemical composition, size, and shape. Aerosol extinction coefficient (sum of light attenuation by scattering and absorption coefficients) is an important optical property for determining aerosol radiative forcing. A broadband cavity enhanced absorption spectroscopy (CEAS) laser-based instrument for measurement of aerosol extinction has been created with a minimum detectable extinction coefficient of 8x10-8 cm-1 for 10-ms collection time. This thesis details the development and validation of these cavity enhanced spectroscopy based instruments.Item Open Access Cavity enhanced Thomson scattering for plasma diagnostics(Colorado State University. Libraries, 2019) Friss, Adam J., author; Yalin, Azer P., advisor; Marchese, Anthony J., committee member; Polk, James E., committee member; Williams, John D., committee member; Yost, Dylan C., committee memberMeasurements of electron number density (nₑ) and electron energy distribution function (EEDF) are of great importance to the study of weakly ionized plasmas, such as those used in laser preionization, semiconductor processing and fabrication, electric propulsion devices, and atmospheric pressure plasmas. Currently, these parameters can be measured by physical probes, e.g. Langmuir probes, or with the use of non-intrusive Laser Thomson Scattering (LTS). While physical probe measurements have been an indispensable tool of the plasma physics community, they affect plasma source operation and result in unwanted plasma perturbation. LTS measurements are appealing due to the non-perturbing nature of the technique, but suffer from low signal levels and optical interference, making application to low-density plasma systems very challenging. This dissertation describes the development of a novel cavity enhanced Thomson scattering (CETS) diagnostic that enables sensitive, non-perturbing measurements of plasma properties. The technique is based upon frequency locking a high-power, narrow-linewidth continuous wave (CW) laser source to a high-finesse optical cavity to build-up intra-cavity power to a level where it can serve as an interrogation laser source. In this way, intra-cavity powers as high as ~12 kW have been generated from a ~5 W laser source and sensitive measurements on a plasma source and gas samples placed within the optical cavity were performed. Despite the CETS technique being widely applicable to a variety of plasma sources, this work focused on the measurement of electric propulsion devices, such as hollow cathodes and Hall effect thrusters. These devices are used as in-space propulsion systems on satellites and scientific probes and may be used as the primary in-space propulsion systems for exploration of the Moon, Mars, and beyond. This work describes the development of the CETS diagnostic including the cavity locking approach, creation of a gas and plasma scattering model, and the development of both a low- and high-power experimental instrument. CETS is demonstrated by performing rotational Raman and Rayleigh scattering measurements on a variety of gases and by performing Thomson scattering measurements in the plume of a hollow cathode. The cathode measurement campaign was conducted over a range of operating conditions, and electron densities and temperatures in the range of ~10¹² cm⁻³ and ~3 eV were measured. Finally, a mobile fiber coupled version of the CETS setup designed for use in large vacuum facilities is presented, and Thomson scattering measurements made with the mobile instrument in the plume of a hollow cathode are discussed.Item Open Access Characterization of plasma conductivity by laser Thomson scattering in a high-voltage laser-triggered switch(Colorado State University. Libraries, 2023) Gottfried, Jacob A., author; Yalin, Azer P., advisor; Dumitrache, Ciprian, committee member; Rocca, Jorge, committee memberHigh-voltage laser-triggered switches (HV-LTSs) are used in pulsed-power applications where low jitter and high current are required. The switches allow operation in the mega-ampere, megavolt regime while maintaining low insertion losses. Low inductance HV-LTS designs have shown discrepancies between modeled and experimental behavior, reinvigorating interest in the physics of HV-LTS operation. Detailed spatially- and temporally- resolved measurements of plasma properties within the switches could contribute to validating and advancing numeric models of these systems by checking the assumptions used in their derivation. To date, there is minimal experimental data detailing the evolution of plasma properties during switch operation. This work investigates HV-LTS plasma channel conductivity (the assumption within current models drawing the most critique) during the rising edge of the current pulse through both derivative (V-Dot) electrical probes and electron temperature measurements via laser Thomson scattering. A HV-LTS testbed utilizing an aqueous (variable impedance) resistive load was designed to produce experimental conditions found in larger pulsed power applications. This work describes the design of the load and experimental results under a variety of load conditions and operating voltages of 5 - 6 kV. The results indicate the electron temperature increases during the rising edge of the current pulse, suggesting that the plasma conductivity is temporally evolving. Further, electrical measurements show an increase in plasma conductivity during the rising edge of the current pulse. Evidence from both optical and electrical measurements calls into question the assumption of a temporally constant plasma conductivity as both the optical and electrical diagnostics show a temporally increasing plasma conductivity during the rising edge of the current pulse.Item Open Access Continuous-wave cavity ring down spectroscopy sensor for Hall thruster erosion measurement(Colorado State University. Libraries, 2011) Tao, Lei, author; Yalin, Azer P., advisor; Marchese, Anthony J., committee member; Menoni, Carmen S., committee member; Williams, John D., committee memberHall thruster and other Electric propulsion (EP) devices have become appealing alternatives to traditional chemical propulsion thrusters for space applications due to this high specific impulse (Isp), which allows high fuel efficiency. However, the uncertainty of the lifetime for Hall thruster hinders its development in future applications requiring a long operational time (several thousands of hours). Sputter erosion of boron nitride (BN) acceleration channel wall is principal lifetime limitation for Hall thrusters. The sputtered particles can redeposit causing a critical contamination effect. There is an urgent need for improved experimental tools to understand the BN sputter erosion process and lifetime assessment for Hall thrusters. The present research applies continuous wave cavity ring down Spectroscopy (CW-CRDS) as a diagnostic tools to study the sputter erosion process for Hall thrusters. Two CW-CRDS erosion sensors have been developed for in situ monitoring of sputtered manganese (Mn) and BN. As a stepping stone towards BN detection, a Mn erosion sensor was first developed. This sensor is based upon detection of Mn atoms via an absorption line from ground state at a wavelength of 403.076 nm. Measurements of sputtered Mn atom number density and its hyperfine structure are presented. Additionally, end-point detection has been done for a multilayer target, which can be potentially applied to the industrial sputtering systems. The same system has also been applied for detecting eroded atoms from the acceleration channel wall in an anode layer type Hall thruster. The results show the validity of the CW-CRDS erosion sensor for Hall thruster lifetime estimation. A BN erosion sensor has also been developed for the detection of sputtered boron atoms from Hall thrusters by probing atomic absorption lines of boron (250 nm) with CW-CRDS. A photonic crystal fiber was used to couple the ultraviolet laser light to the cavity within the vacuum chamber. The experimental detection limits and signal-to-noise values show potential for Hall thruster BN erosion studies. Finally, the velocity distributions of sputtered boron atoms at different ion energies were measured with laser induced fluorescence (LIF). These velocity distribution are necessary for interpretation of signals from the BN erosion sensor.Item Open Access Development of a Hall thruster test facility(Colorado State University. Libraries, 2012) Leach, Randolph W., author; Yalin, Azer P., advisor; Williams, John D., committee member; Menoni, Carmen S., committee memberThe present thesis details the development of a Hall thruster test facility for low power (<600 W) thrusters. The facility is based on a vacuum chamber, two standard cryogenic pumps and one modified cryogenic pump. The modified cryogenic pump is outfitted with custom built internal components, which are referred to as a cryosail. Estimation as well as measurement of pumping speeds of the two cryogenic pumps and cryosail were conducted resulting in an overall measured pumping speed of 10,500 L/s for Xenon. The ultimate base pressure of the system was 4x10-8 Torr. A SPT-70 Hall thruster was operated at various conditions and set points to include fine tuning the current to the magnets to find efficient thruster operation. Ion current densities at points downstream of the thruster's exit plane were examined by a Faraday probe. Although operation at nominal thruster operating conditions was not achieved, likely due to a problem with magnetic coils, the thruster operation did allow preliminary measurements by Cavity Ring-Down Spectroscopy of sputtered Boron originating from the thruster channel wall.Item Open Access Development of a high-voltage laser triggered switch facility including initial optical and electrical diagnostics(Colorado State University. Libraries, 2019) Rose, Charles E., author; Yalin, Azer P., advisor; Menoni, Carmen S., committee member; Yourdkhani, Mostafa, committee memberPulsed power programs have been part of the United States strategic plan to address the nation's energy and defense needs since the 1960s. With escalating energy demand, one of the greatest challenges of our time is to develop clean and reliable energy sources with controlled fusion being an exciting and favorable candidate. Developing this technology has been an arduous and taxing effort with a breakthrough (supposedly) coming just around the corner for decades. Arguably, one of the leading testbeds for fusion research is Sandia National Laboratories (SNL) Z machine which is part of SNL's pulsed power program. The Z machine can create fusion-like conditions and allows the global research community to investigate pathways forward to a viable fusion reactor. Integral to developing future pulsed power technology and the next Z-pinch style machines, high voltage spark gap switches are an active research area and the focus of this thesis.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 Development of mobile open-path cavity ring-down spectrometer for measurement of trace atmospheric methane gas(Colorado State University. Libraries, 2018) McHale, Laura, author; Yalin, Azer P., advisor; Marchese, Anthony, committee member; Olsen, Daniel, committee member; Pierce, Jeffrey, committee memberUse in recent decades of methane as a 'clean' alternative to coal and gasoline has seen a rapid increase in natural gas extraction in the United States. Although combustion of methane produces less CO2 than traditional fuels, it is a powerful greenhouse gas with a 20 year Global Warming Potential (GWP20) that is 84x that reported for CO2 in the latest IPCC report; therefore, the promise of natural gas as a clean fuel can only by realized if emissions of uncombusted gas are sufficiently low. To address this problem, there is a need for both regional (basin wide) measurements of methane emissions to determine global levels, as well as localized measurements to allow identification and reduction of emissions ("leaks") from specific equipment. The goal of this research is to develop a mobile open-path cavity ring-down spectroscopy (CRDS) sensor for localized measurements of atmospheric methane. While designed with the oil and gas industry in mind, the technology also has application to study emissions from agricultural operations and those from other sectors. This thesis presents development from proof-of-concept open-path sensor through two mobile iterations. CRDS can provide fast, non-intrusive, sensitive measurements; but in contrast to available instruments, the focus is on open-path operation (no flow-cell and pump) to provide opportunities for significant weight, size and power reductions to increase the mobility of the technique (<4 kg, <25 W). Challenges of open-path operation, such as fitting broadened spectral peaks, preserving mirror cleanliness and techniques for removing signal noise due to aerosol particles are addressed. The sensor is based on widely available and mature engineering near-infrared (NIR) opto-electronic components that have been developed for the telecom industry. Sensor validation with known methane concentrations show that the open-path sensor is capable of measuring atmospheric concentrations in the range of ~1.8-20+ ppmv at a rate of 1-3 Hz. Sensitivity studies using Allan variance techniques show sensitivity of < 20 ppbv in 1 – adequate for practical leak detection of small plumes <1 ppmv. Comparisons against a commercially available closed path sensor in mobile deployments are presented, along with mobile measurements from natural gas facilities in Platteville, CO and Washington County, PA. Finally, integration of the sensor onto a UAS platform for airborne measurements of methane and ammonia from agricultural applications is discussed.Item Open Access Fabrication of omniphobic and superomniphobic surfaces(Colorado State University. Libraries, 2017) Pendurthi, Anudeep, author; Kota, Arun K., advisor; Yalin, Azer P., advisor; Kipper, Matt J., committee memberSuperomniphobic surfaces (i.e., surfaces that are extremely repellent to both high surface tension liquids like water and low surface tension liquid like oils and alcohols) can be fabricated through a combination of surface chemistry that imparts low solid surface energy and a re-entrant surface texture. Recently, surface texturing with lasers has received significant attention because laser texturing is scalable, solvent-free, and can produce a monolithic texture (i.e., a texture that is an integral part of the surface unlike a coating that is deposited on the underlying substrate) on virtually any material. In this work, we fabricated nanostructured omniphobic and superomniphobic surfaces with stainless steel 430, stainless steel 316, stainless steel 304, titanium, aluminum and glass surfaces using a simple, inexpensive and commercially available CO2 laser engraver. Further, we demonstrated that the nanostructured omniphobic and superomniphobic surfaces fabricated using our laser texturing technique can be used to design patterned surfaces, surfaces with discrete domains of the desired wettability and on-surface microfluidic devices. Systematic experiments were conducted to evaluate the importance of various laser parameters to fabricate these omniphobic and superomniphobic surfaces. Also, the performance of these surfaces under adverse acidic and basic conditions was evaluated systematically. In addition to surface texturing with lasers, in this work, we also report a simple and versatile method to fabricate superomniphobic glass microfiber paper by growing silicone nanofilaments using trichloromethylsilane (TCMS).Item Open Access Laser diagnostic method for plasma sheath potential mapping(Colorado State University. Libraries, 2016) Walsh, Sean P., author; Yalin, Azer P., advisor; Williams, John D., committee member; Rocca, Jorge G., committee memberElectric propulsion systems are gaining popularity in the aerospace field as a viable option for long term positioning and thrusting applications. In particular, Hall thrusters have shown promise as the primary propulsion engine for space probes during interplanetary journeys. However, the interaction between propellant xenon ions and the ceramic channel wall continues to remain a complex issue. The most significant source of power loss in Hall thrusters is due to electron and ion currents through the sheath to the channel wall. A sheath is a region of high electric field that separates a plasma from a wall or surface in contact. Plasma electrons with enough energy to penetrate the sheath may result emission of a secondary electron from the wall. With significant secondary electron emission (SEE), the sheath voltage is reduced and so too is the electron retarding electric field. Therefore, a lower sheath voltage further increases the particle loss to the wall of a Hall thruster and leads to plasma cooling and lower efficiency. To further understand sheath dynamics, laser-induced fluorescence is employed to provide a non-invasive, in situ, and spatially resolved technique for measuring xenon ion velocity. By scanning the laser wavelength over an electronic transition of singly ionized xenon and collecting the resulting fluorescence, one can determine the ion velocity from the Doppler shifted absorption. Knowing the velocity at multiple points in the sheath, it can be converted to a relative electric potential profile which can reveal a lot about the plasma-wall interaction and the severity of SEE. The challenge of adequately measuring sheath potential profiles is optimizing the experiment to maximize the signal-to-noise ratio. A strong signal with low noise, enables high resolution measurements and increases the depth of measurement in the sheath, where the signal strength is lowest. Many improvements were made to reduce the background luminosity, increase the fluorescence intensity and collection efficiency, and optimize the signal processing equipment. Doing so has allowed for a spatial resolution of 60 microns and a maximum depth of measurement of ~2 mm depending on conditions. Sheaths surrounding common Hall thruster ceramics at various plasma conditions were measured in an attempt to determine the effect of SEE and a numerical analysis of the plasma-wall interactions was conducted to further understand the phenomena and compare against obtained data.Item Open Access Laser diagnostic methods for plasma sheath potential mapping and electric field measurement(Colorado State University. Libraries, 2013) Rath, Jordan L., author; Yalin, Azer P., advisor; Williams, John D., committee member; Rocca, Jorge G., committee memberThis thesis presents the development of two laser diagnostic approaches for electric field measurements in plasmas and gases. Hall effect thrusters, and other electric propulsion devices, have limited lifetimes due to the erosion of components by ion bombardment of surfaces. A better understanding of the electric field structure in the plasma sheaths near these surfaces would enable researchers to improve thruster designs for extended lifetime and higher efficiency. The present work includes the development of a laser induced fluorescence technique employing a diode laser at 835 nm to measure spatially resolved xenon ion velocity distribution functions (IVDFs) near plasma-surface interfaces (sheaths), from which electric field and spatially-resolved potentials can be determined. The optical setup and demonstrative measurements in a low-density multi-pole plasma source are presented. Also included in this thesis is development of a cavity-enhanced polarimetry technique for electric field measurements in gases via the optical Kerr effect. The high finesse optical cavity allows sensitive measurement of the electric field induced birefringence, improving upon the detection limits of past work using related multi-pass techniques. Experimental results are presented for carbon dioxide, nitrogen, oxygen and air along with comparisons to model predictions based on published Kerr constants.Item Open Access Measurement of ammonia emission from agricultural sites using open-path cavity ring-down spectroscopy and wavelength modulation spectroscopy based analyzers(Colorado State University. Libraries, 2018) Shadman, Soran, author; Yalin, Azer P., advisor; Marchese, Anthony J., committee member; Olsen, Daniel B., committee member; Ham, Jay, committee memberAgricultural activities and animal feedlot operations are the primary sources of emitted ammonia into the atmosphere. In the US, 4 Tg of ammonia is emitted every year into the atmosphere which ~%75 of that is due to these major sources. Ammonia is the third most abundant nitrogen containing species in the atmosphere and it has important impacts on atmospheric chemistry, health, and the environment. It is a precursor to the formation of aerosols and its deposition in pristine and aquatic systems leads to changes in ecosystem properties. Quantifying the dry deposition rate of ammonia in the first few kilometers of feedlots is crucial for better understanding the impacts of livestock and agricultural operations on environment. Therefore, fast, precise, and portable sensors are needed to quantify ammonia emission from its major sources. Absorption spectroscopy is a reliable technique by which compact and sensitive sensors can be developed for ammonia (and other gaseous species) detection. An open-path absorption spectroscopy based sensor allows ambient air to flow directly through its measurement region which leads to high-sensitivity and fast-response measurements. In this study, two open-path absorption based ammonia sensors using two techniques are developed: cavity ring-down spectroscopy (CRDS) and wavelength modulation spectroscopy (WMS). The CRDS and WMS based sensors show the sensitivity of ~1.5 ppb (at 1 second) and ~4 ppb (at 1 second), respectively. In both sensors, a quantum cascade laser (QCL) is utilized as the light source to cover the strongest absorption feature of ammonia in the mid-infrared (MIR) spectral region. It is the first demonstration of an open-path CRDS based sensor working in mid-infrared MIR, to our knowledge. The WMS based sensor developed in this study is low power (~25 W) and relatively lightweight (~4 kg). The low power consumption and compact size enables the sensor to be deployed on a commercialized unmanned aerial system (UAS) for aerial measurements. The combination of this sensor and another compact CRDS based methane sensor is used for simultaneous measurements of ammonia and methane (ground based and aerial). Methane is another important species emitted from the feedlots with a long lifetime (~10 years). It is nonreactive and thus not lost by dry deposition. Therefore, methane concentration is only influenced by dispersion while the ammonia concentration is affected by both deposition and dispersion. The dry deposition of ammonia nearby the concentrated animal feeding operations (CAFOs), as one of the major sources of ammonia, can be determined by measuring the decrease in the [NH3]/[CH4] ratio downwind.Item Open Access Modeling methane emissions from US natural gas operations: national gathering station emission factor development and facility/regional-scale top-down to bottom-up reconciliations(Colorado State University. Libraries, 2017) Vaughn, Timothy L., author; Marchese, Anthony J., advisor; Yalin, Azer P., advisor; Olsen, Daniel B., committee member; Opsomer, Jean D., committee memberUnited States natural gas dry production increased by 47% between 2005 and 2015 due to the widespread use of horizontal drilling and hydraulic fracturing to extract gas from shale and other tight formations. Natural gas production and consumption is projected to continue to increase for the foreseeable future. In 2016, the natural gas supply chain delivered 29% of the energy used in the U.S., and natural gas surpassed coal as the leading electricity generating source for the first time in U.S. history. When combusted, natural gas produces less CO2 per unit energy released compared to coal or petroleum. However, uncombusted methane (the primary component of natural gas) has a global warming potential 30 times higher than CO2 on a 100 year time horizon (including oxidation to CO2, but excluding climate-carbon feedbacks). Therefore, the net greenhouse gas impacts resulting from displacement of coal and petroleum by natural gas depend on the emission rate of uncombusted natural gas. Short term climate benefits resulting from coal substitution, for example, are lost if the net rate of methane (CH4) emission from the natural gas supply chain exceeds 3—4% . Three studies were conducted to quantify CH4 emissions from the natural gas industry. In particular, these studies focused on quantifying emissions from the gathering and processing sector and reconciling emissions estimates developed using top-down (tracer flux and aircraft) vs. bottom-up (on-site component-level) measurement approaches. In the first study, facility-level CH4 emissions measurements were made at 114 natural gas gathering facilities and 16 processing plants in 13 U.S. states during a 20-week field campaign conducted from October 2013 through April 2014. Measurement results were combined with facility counts obtained from state air permit databases and national inventories in a Monte Carlo simulation to estimate CH4 emissions from U.S. natural gas gathering and processing operations. Annual CH4 emissions from normal operations at gathering facilities totaled 1699 Gg (95% CI=1539—1863 Gg), while normal operations at processing plants totaled 505 Gg (95% CI=459—548 Gg). CH4 emissions from abnormal operations at gathering facilities were estimated in a separate Monte Carlo simulation based on field observations and a sub-set of field measurements. These emissions totaled 169 Gg (+426%/-96%). In the second study, coordinated dual-tracer, aircraft-based, and direct component-level measurements were made at midstream natural gas gathering and boosting stations in the Fayetteville shale in Arkansas, USA. On-site component-level measurements were combined with engineering estimates to generate comprehensive facility-level CH4 emission rate estimates ("study on-site estimates (SOE)") comparable to tracer and aircraft measurements. Concurrent measurements at 14 normally-operating facilities showed a strong correlation between tracer and SOE, but indicated that tracer measurements estimated lower emissions (regression of tracer to SOE=0.91 (95% CI=0.83—0.99, R2=0.89). Tracer and SOE 95% confidence intervals overlapped at 11/14 facilities. Contemporaneous measurements at six facilities suggested that aircraft measurements estimated higher emissions than SOE. Aircraft and study on-site estimate 95% confidence intervals overlapped at 3/6 facilities. In the third study, a detailed spatiotemporal inventory model was developed and used to reconcile top down and bottom-up CH4 emission estimates from natural gas infrastructure and other sources in the Fayetteville shale on two consecutive days. On Thursday October 1, 2015 13:00—15:00 CDT top-down aircraft mass balance flights estimated 28.7 (20.1—37.3 Mg/h 95% CI) from the study area, while the bottom-up ground level area estimate predicted 23.9 (20.9—27.3 Mg/h 95% CI). On Friday October 2, 2015 14:30—16:30 CDT top-down estimated 36.7 (21.3—52.1 Mg/h 95% CI), while bottom-up estimated 21.1 (18.4—24.2 Mg/h 95% CI). Production and gathering activities were the largest contributors to modeled CH4 emissions. In contrast to prior studies, comparisons on two consecutive days indicated overlapping confidence intervals between top-down aircraft estimates and bottom-up inventory-driven estimates. Operator participation and extensive activity data proved critical in understanding emissions as observed by aircraft. In particular, the agreement obtained was possible only because bottom-up models included the variability in production maintenance activities, which showed substantially higher emissions during daytime hours when aircraft-based measurements were performed. Results indicated that that poor activity estimates (counts and timing) for large episodic events likely drives divergence in CH4 emission estimates from production basins, and that even more precise activity data would be required to improve agreement between these two approaches.Item Open Access Novel laser ignition technique using dual-pulse pre-ionization(Colorado State University. Libraries, 2017) Dumitrache, Ciprian, author; Yalin, Azer P., advisor; Marchese, Anthony J., advisor; Gao, Xinfeng, committee member; Kirkpatrick, Allan T., committee member; Van Orden, Alan, committee memberRecent advances in the development of compact high power laser sources and fiber optic delivery of giant pulses have generated a renewed interest in laser ignition. The non-intrusive nature of laser ignition gives it a set of unique characteristics over the well-established capacitive discharge devices (or spark plugs) that are currently used as ignition sources in engines. Overall, the use of laser ignition has been shown to have a positive impact on engine operation leading to a reduction in NOx emission, fuel saving and an increased operational envelope of current engines. Conventionally, laser ignition is achieved by tightly focusing a high-power q-switched laser pulse until the optical intensity at the focus is high enough to breakdown the gas molecules. This leads to the formation of a spark that serves as the ignition source in engines. However, there are certain disadvantages associated with this ignition method. This ionization approach is energetically inefficient as the medium is transparent to the laser radiation until the laser intensity is high enough to cause gas breakdown. As a consequence, very high energies are required for ignition (about an order of magnitude higher energy than capacitive plugs at stoichiometric conditions). Additionally, the fluid flow induced during the plasma recombination generates high vorticity leading to high rates of flame stretching. In this work, we are addressing some of the aforementioned disadvantages of laser ignition by developing a novel approach based on a dual-pulse pre-ionization scheme. The new technique works by decoupling the effect of the two ionization mechanisms governing plasma formation: multiphoton ionization (MPI) and electron avalanche ionization (EAI). An UV nanosecond pulse (λ=266 nm) is used to generate initial ionization through MPI. This is followed by an overlapped NIR nanosecond pulse (λ=1064 nm) that adds energy into the pre-ionized mixture into a controlled manner until the gas temperature is suitable for combustion (T=2000-3000 K). This technique is demonstrated by attempting ignition of various mixtures of propane-air and it is shown to have distinct advantages when compared to the classical approach: lower ignition energy for given stoichiometry than conventional laser ignition (~20% lower), extension of the lean limit (~15% leaner) and improvement in combustion efficiency. Moreover, it is demonstrated that careful alignment of the two pulses influences the fluid dynamics of the early flame kernel growth. This finding has a number of implications for practical uses as it demonstrates that the flame kernel dynamics can be tailored using various combinations of laser pulses and opens the door for implementing such a technique to applications such as: flame holding and flame stabilization in high speed flow combustors (such as ramjet and scramjet engines), reducing flame stretching in highly turbulent combustion devices and increasing combustion efficiency for stationary natural gas engines. As such, the work presented in this dissertation should be of interest to a broad audience including those interested in combustion research, engine operation, chemically reacting flows, plasma dynamics and laser diagnostics.Item Open Access Preliminary development and testing of an open-path hydrocarbon sensor for oil and gas facility monitoring(Colorado State University. Libraries, 2019) Farris, Betsy M., author; Yalin, Azer P., advisor; Fischer, Emily V., committee member; Jathar, Shantanu H., committee memberWe developed an open-path laser absorption sensor for detection of unspeciated hydrocarbons for oil and gas production facility fence line monitoring. Such sensors can aid in maintaining air quality standards by quantifying greenhouse gas emissions and detecting emissions that cause adverse health effects. Our initial design employs a single-path detection system, though future implementations may use multiple paths for large-scale facility monitoring. The sensor uses a compact mid-infrared laser source in the spectral region of ~3.3 µm to measure absorption of several hydrocarbon species and is intended for open-paths of ~100 m to 1 km. Spectral simulations show that for typical conditions the hydrocarbons cause a transmission reduction of ~10% allowing for a robust measurement. The initial prototype system uses a helium-neon (He:Ne) laser at 3.391 µm for which signal contributions from methane and non-methane hydrocarbons are comparable. Closed-cell tests were performed with diluted methane (~150-250 ppm) to validate the transmission signals and showed good agreement with expected (calculated) values to within ~10%. The system employs a reference leg, with a 2nd detector (near the source), to normalize for laser power fluctuations. For improved signal-to-noise, particularly for detection of small concentrations and transmission changes, we employ phase-sensitive detection with a mechanical chopper and software based lock-in amplifier. This detection scheme, when employed in the field, allows measurement of transmission signals with stability <0.5% (based on coefficient of variation over 60 s). The portable field sensor system uses two refractive telescopes (2" diameter optics), a transmitter and receiver co-located on a mobile optical breadboard, and a reflector dictating the pathlength. We performed initial tests with pathlengths up to ~25 m (one way), though the design should allow paths in excess of 100 m. Methane was released for initial field tests at known flow rates near the center of the beam path. Transmission signals in agreement with expectations (given uncertainties in the wind and plume dispersion) were observed. The system should allow detection of leaks (emissions) for mass flows as low as ~0.1 g/s of methane (or equivalent optical signal from other species resulting in a 1% change in signal) for the case where the source is ~150 m from the beam path and under typical atmospheric conditions. Recommendations for future modifications are provided based on potential shortcomings identified by initial field testing. Initial field testing also proved that this technology could be a viable low-cost solution for hydrocarbon detection.Item Open Access Real-time erosion measurements of the HiVHAc and SPT-70 Hall thrusters via cavity ring-down spectroscopy(Colorado State University. Libraries, 2014) Lee, Brian Christopher, author; Lundeen, Stephen R., advisor; Yalin, Azer P., advisor; Roberts, Jacob L., committee member; Krueger, David A., committee member; Williams, John D., committee memberElectric propulsion has moved to the forefront of in-space propulsion in recent years. By making exceptionally efficient use of propellant, electric propulsion devices have significantly reduced the cost of some missions and enabled others, which had not previously been possible. Among these devices, Hall thrusters have shown particular promise. However, for many thrusters of interest, sputter erosion of the insulating channel remains a problem and continues to limit the thruster lifetime. Diagnostic tools to assess the absolute channel erosion rate rapidly remain limited. This thesis describes the use of ultraviolet cavity ring-down spectroscopy (CRDS) as a real-time diagnostic of sputtered boron atoms in the thruster plume. Cavity ring-down spectroscopy is an ultra-sensitive laser-absorption technique which is particularly apt at measuring trace species number densities in the gas phase. In this work, ground-state atomic boron, which was sputtered from the thruster channel, was measured near 250 nm. The interrogating laser was swept across the exit plane of a Hall thruster, providing spatially-resolved boron number density measurements. Additionally, laser-induced fluorescence was used to measure the velocity of sputtered boron along the thruster axis, which were the first measurements of its kind. The measured boron number density and velocity component together provided a total boron flux from the thruster, and therefore, a channel erosion rate. Channel erosion rates of the NASA HiVHAc and the SPT-70 Hall thrusters were measured using CRDS. Absolute erosion rates and trends with operating condition were investigated. Both thrusters were found to erode at rates proportional to the discharge power, which is consistent with the available literature. Profilometry was also used to measure the channel erosion rate of the SPT-70 thruster and revealed a factor of ~5 disagreement with estimates made by CRDS. Calcium fluoride (CaF2) prism retroreflectors were developed, for the first time, as a means to improve both the bandwidth and finesse of optical cavities in the ultraviolet region. The CRDS technique used in thruster erosion measurements employed multilayer dielectric mirrors, which have relatively poor performance in the ultraviolet region. Calcium fluoride prism retroreflectors show promise to outperform the best available dieletric mirrors at 250 nm as well as provide broadband cavity operation. The design, construction, and characterization of the CaF2 prisms is presented.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.