Browsing by Author "Yalin, Azer P., committee member"
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Item Open Access A high-speed mass spectrometer for characterizing flash desorbed species in pulsed power applications(Colorado State University. Libraries, 2022) Ossareh, Susan J., author; Williams, John D., advisor; Yalin, Azer P., committee member; Roberts, Jacob L., committee memberSandia National Laboratories operates the largest pulsed power facility in the world that hosts the Z machine that is utilized for research in fusion, energy, and national security. It can simulate extreme environments in these research areas in a single "shot" or "pulse of power," where large capacitor banks are rapidly discharged simultaneously, sending power to the center of the machine where a load is compressed into a z-pinch. A shot on the Z machine occurs in 150ns with peak currents on the order of 26 mega-amperes. However, there is a power flow obstacle that limits its ability to reach these extreme conditions. Approximately 1-3 MA of current is lost per shot. This could be partially attributed to chemisorbed contaminants on the cathode and anode stack in the center section of the machine being liberated in a flash desorption process, forming a conductive plasma between the anode and cathode electrodes that causes current to bypass the load and limits the power flow into the load. This project is focused on the design and development of a high-speed mass spectrometer to make measurements of the gasses evolved from the electrodes that are heated to 1000°C in 100 nanoseconds. The measurements from this diagnostic would allow for more accurate predictive modeling of current loss for Next Generation Pulsed Power Drivers, such as the Z machine. Since a probe does not exist commercially, the project requires the development of new mass spectrometry technology, however a pre-existing probe was used to begin the design process. This probe is known as the Energy and Velocity Analyzer for Distributions of Electric Rockets (EVADER) probe, which combines an electrostatic analyzer and a Wien velocity filter. Within this study, two different plasma sources were used separately to simulate the plasma generated in the Z machine, and steady state measurements were made of the ions produced while working towards taking transient measurements. The design and development efforts described in this thesis were guided by: (1) using the EVADER to collect steady state data in its original configuration as a basis of comparison, (2) then replacing an ammeter in the experimental system with a transimpedance amplifier (TIA) circuit to speed up the data sampling rate over that of the ammeter, (3) incorporate a micro-channel plate within the probe to amplify the current feed to the TIA and enable even faster data sampling rates, and (4) design a high speed electric shutter to quickly turn "on" and "off" ion flow to the probe to enable measurement of the temporal response of the probe with the transimpedance amplifier and micro-channel plate elements. The end goal of the project is to improve transient performance of a probe from 10s of seconds to 10s of micro-seconds in a stepwise manner to support pulsed power research.Item Open Access A new measurement of the 2S1/2-8D5/2 transition in atomic hydrogen(Colorado State University. Libraries, 2021) Brandt, Adam D., author; Yost, Dylan C., advisor; Yalin, Azer P., committee member; Roberts, Jacob L., committee member; Field, Stuart B., committee memberHigh-precision spectroscopy of simple atoms provides input data that can be used to extract fundamental constants and to test Standard Model theory. Hydrogen, the simplest element, has played a historically significant role in the development of fundamental theory and, more recently, provides important data for the proton radius puzzle. In this thesis, we will describe a new measurement of the 2S1/2-8D5/2 transition on a cryogenic hydrogen beam. We will overview the measurement scheme and experimental apparatus, then present analysis and systematic characterization important to the spectroscopy. Finally, we will present our preliminary determination of the proton radius and the Rydberg constant using our value for the 2S1/2-8D5/2 combined with the previously measured 1S-2S transition.Item Open Access An experimental investigation of heaterless hollow cathode ignition(Colorado State University. Libraries, 2020) Ham, Ryan K., author; Williams, John D., advisor; Yalin, Azer P., committee member; Marconi, Mario C., committee member; Tomasel, Fernando G., committee memberA hollow cathode is a specially designed plasma source that is capable of driving a large electron emission current throughout the course of a remarkably long lifetime. Given these characteristics, hollow cathodes are commonly used as electron sources in state-of-the-art plasma thrusters. Modern advancements in small-satellite technology have led to an increased demand for low-power electric propulsion systems. Given the high thrust-to-power ratio and flight-proven heritage of Hall-effect thrusters, efforts are currently being made to downsize these thrusters to a considerably small scale. By forgoing the use of a heater, heaterless hollow cathodes provide several advantages that are best realized in miniaturized Hall-effect thrusters. Unfortunately, the lack of a cathode heater gives rise to nontrivial complications in the process of igniting a plasma discharge, along with reason to believe that life-limiting cathode erosion could occur during ignition. These concerns have resulted in a lack of confidence that heaterless hollow cathode technology can endure the rigors of spaceflight qualification. In this research, heaterless hollow cathode ignition behavior was characterized. In doing so, it was found that repeatable and reliable instant start ignition behavior can be achieved when using a high propellant mass flow rate. To provide this flow condition without placing a large burden on a propellant feed system, a novel gas flow mechanism was developed and characterized. To investigate whether instant start ignition causes cathode erosion, a series of tests were performed in which heaterless hollow cathodes were subjected to a large number of ignition cycles. Microscopy revealed no indication of cathodic arc activity, and no other evidence of life-limiting erosion were observed. The instant start ignition process appears to be a viable approach to heaterless hollow cathode ignition, and we believe it provides a means for heaterless hollow cathode technology to be integrated into spaceflight propulsion systems.Item Open Access Applying model-based systems engineering in search of quality by design(Colorado State University. Libraries, 2022) Miller, Andrew R., author; Herber, Daniel R., advisor; Bradley, Thomas, committee member; Miller, Erika, committee member; Simske, Steve, committee member; Yalin, Azer P., committee memberModel-Based System Engineering (MBSE) and Model-Based Engineering (MBE) techniques have been successfully introduced into the design process of many different types of systems. The application of these techniques can be reflected in the modeling of requirements, functions, behavior, and many other aspects. The modeled design provides a digital representation of a system and the supporting development data architecture and functional requirements associated with that architecture through modeling system aspects. Various levels of the system and the corresponding data architecture fidelity can be represented within MBSE environment tools. Typically, the level of fidelity is driven by crucial systems engineering constraints such as cost, schedule, performance, and quality. Systems engineering uses many methods to develop system and data architecture to provide a representative system that meets costs within schedule with sufficient quality while maintaining the customer performance needs. The most complex and elusive constraints on systems engineering are defining system requirements focusing on quality, given a certain set of system level requirements, which is the likelihood that those requirements will be correctly and accurately found in the final system design. The focus of this research will investigate specifically the Department of Defense Architecture Framework (DoDAF) in use today to establish and then assess the relationship between the system, data architecture, and requirements in terms of Quality By Design (QbD). QbD was first coined in 1992, Quality by Design: The New Steps for Planning Quality into Goods and Services [1]. This research investigates and proposes a means to: contextualize high-level quality terms within the MBSE functional area, provide an outline for a conceptual but functional quality framework as it pertains to the MBSE DoDAF, provides tailored quality metrics with improved definitions, and then tests this improved quality framework by assessing two corresponding case studies analysis evaluations within the MBSE functional area to interrogate model architectures and assess quality of system design. Developed in the early 2000s, the Department of Defense Architecture Framework (DoDAF) is still in use today, and its system description methodologies continue to impact subsequent system description approaches [2]. Two case studies were analyzed to show proposed QbD evaluation to analyze DoDAF CONOP architecture quality. The first case study addresses the analysis of DoDAF CONOP of the National Aeronautics and Space Administration (NASA) Joint Polar Satellite System (JPSS) ground system for National Oceanic and Atmospheric Administration (NOAA) satellite system with particular focus on the Stored Mission Data (SMD) mission thread. The second case study addresses the analysis of DoDAF CONOP of the Search and Rescue (SAR) navel rescue operation network System of Systems (SoS) with particular focus on the Command and Control signaling mission thread. The case studies help to demonstrate a new DoDAF Quality Conceptual Framework (DQCF) as a means to investigate quality of DoDAF architecture in depth to include the application of DoDAF standard, the UML/SysML standards, requirement architecture instantiation, as well as modularity to understand architecture reusability and complexity. By providing a renewed focus on a quality-based systems engineering process when applying the DoDAF, improved trust in the system and data architecture of the completed models can be achieved. The results of the case study analyses reveal how a quality-focused systems engineering process can be used during development to provide a product design that better meets the customer's intent and ultimately provides the potential for the best quality product.Item Open Access Combustion phenomena in biomass gasifier cookstoves(Colorado State University. Libraries, 2016) Tryner, Jessica, author; Marchese, Anthony J., advisor; Willson, Bryan, committee member; Yalin, Azer P., committee member; Peel, Jennifer, committee memberApproximately 2.8 billion people (~40% of the global population) rely on solid fuels, such as wood, charcoal, agricultural residues, and coal, for cooking. Exposure to emissions resulting from incomplete combustion of solid fuels leads to many adverse health impacts. These health impacts have motivated the development of solid-fuel cookstoves that reduce user exposure to carbon monoxide (CO) and fine particulate matter (PM2.5). In recent years, rating systems and emission rate targets for solid-fuel cookstove performance have been proposed. The aspirational targets included in these systems (e.g., Tier 4 in the ISO IWA tiers) have encouraged the development of cookstoves that reduce emissions of CO and PM2.5 by more than 50% and 95%, respectively, compared to a baseline three-stone fire. In a top-lit up draft (TLUD) gasifier cookstove, solid biomass fuel is gasified and the resulting gaseous fuel is mixed with secondary air above the fuel bed to produce the flame that heats the cooking surface. Household biomass cookstoves that utilize gasifier designs have attracted interest due to their demonstrated ability to emit less CO and PM2.5 per unit of energy delivered to the cooking surface than other cookstove designs. Unfortunately, highly variable performance has also been observed among gasifier cookstoves, and some have been found to emit more CO and PM2.5 than a three-stone fire. Accordingly, three studies were conducted to: (1) identify the sources of the observed variability; (2) characterize the manner in which stove design, fuel properties, and operating mode influenced performance; (3) gain insight into how secondary air velocity affected fuel-air mixing and the flame dynamics in the secondary combustion zone; and (4) evaluate whether or not the reductions in emission rates that are sought could be achieved with the TLUD design. In the first study, five natural draft TLUD design configurations were tested with two fuels (corn cobs and Lodgepole pine pellets) to investigate the variability in performance that had been observed in previous studies. The results indicated that stove design, fuel type, and operator behavior all influenced emissions. Four of the five configurations exhibited lower emissions when fueled with Lodgepole pine pellets than when fueled with corn cobs. Furthermore, large transient increases in CO emission rates were observed when stoves were refueled during operation by adding fresh biomass on top of the hot char bed that was left behind after the previous batch of fuel had gasified. An energy balance model was also developed, using temperature data collected from thermocouples mounted on each configuration, to identify the factors that contributed the most to sub-unity efficiency. The results illustrated that up to 60% of the energy input to the stove as fuel could be left over as char at the end of the test, and whether or not the energy in this char was subtracted from the energy in the fuel consumed during the test when calculating the thermal efficiency of a given configuration had a large effect on the calculated efficiency value. The manner in which cookstove design, fuel properties, and operator behavior affected TLUD performance was investigated in more detail in a second study. Seventeen different stove geometries, 4 primary air flow rates, 4 secondary air flow rates, 5 secondary air temperatures, 4 fuel moisture contents, and 4 different sfuel types were tested in a modular test bed using a procedure specifically designed to capture the low emissions observed during normal operation and the high emissions observed during refueling and char burnout. The lowest high-power emissions measured during normal operation were 1.6 g/MJd-1 CO (90% confidence interval (CI) = 1.1-2.1) and 18 mg/MJd-1 PM2.5 (90% CI = 17-19). These values were well below the Tier 4 targets of 8 g/MJd-1 CO and 41 mg/MJd-1 PM2.5, but post-refueling emissions were always above the Tier 4 targets. Higher secondary air velocities resulted in lower emissions. Changes in fuel type influenced the composition of the producer gas entering the secondary combustion zone during normal operation and sometimes resulted in order of magnitude changes in PM2.5 emissions. Temperature measurements taken in the fuel bed indicated that the stove operated as an inverted downdraft gasifier during normal operation and as a conventional updraft gasifier after refueling. Overall, the results suggest that efforts aimed at reducing users' exposure to CO and PM2.5 emissions from solid fuel combustion need to take fuel type and operator behavior, in addition to stove design, into consideration. The third study was designed to investigate the effects of secondary air velocity on the fuel-air mixing process and flame dynamics in the secondary combustion zone by employing high-speed imaging techniques. Images of OH* chemiluminescence, acetone (which served as a fuel tracer) planar laser-induced fluorescence (PLIF), and OH PLIF were collected at multi-kHz repetition rates in a burner designed to generate a two-dimensional replica of the secondary combustion zone in a gasifier cookstove. This burner featured two opposed planar jets that formed an inverse non-premixed flame in which the air and fuel were in cross flow. Images were collected for various air and fuel velocities. Regular deflecting oscillation of the jets, which has been reported previously for isothermal, non-reacting, unconfined opposed planar jets, was observed in some cases but appeared to be suppressed by convection in the vertical direction and buoyancy effects in other cases. The acetone PLIF images revealed that a high air jet velocity resulted in more extensive mixing of the air and fuel below the height of air injection. As a result, the reaction zone was located further below the top of the burner in comparison to the low air velocity case. These results suggest that higher air jet velocities may lead to lower emissions from gasifier cookstoves as a result of better fuel-air mixing and a lower reaction front location that allows more time for CO and PM to be oxidized before reactions are quenched by the cold cooking surface; however, the literature suggests that unconfined opposed axisymmetric jets do not exhibit deflecting oscillation behavior and, as a result, there are limitations associated with the use of opposed planar jets as a model for the secondary air jets in a gasifier cookstove.Item Open Access Contributions of gas-phase plasma chemistry to surface modifications and gas-surface interactions: investigations of fluorocarbon rf plasmas(Colorado State University. Libraries, 2012) Cuddy, Michael F., author; Fisher, Ellen R., advisor; Levinger, Nancy E., committee member; Rickey, Dawn, committee member; Krummel, Amber, committee member; Yalin, Azer P., committee memberThe fundamental aspects of inductively coupled fluorocarbon (FC) plasma chemistry were examined, with special emphasis on the contributions of gas-phase species to surface modifications. Characterization of the gas-phase constituents of single-source CF4-, C2F6-, C3F8-, and C3F6-based plasmas was performed using spectroscopic and mass spectrometric techniques. The effects of varying plasma parameters, including applied rf power (P) and system pressure (p) were examined. Optical emission spectroscopy (OES) and laser-induced fluorescence (LIF) spectroscopy were employed to monitor the behavior of excited and ground CFx (x = 1,2) radicals, respectively. Mass spectrometric techniques, including ion energy analyses, elucidated behaviors of nascent ions in the FC plasmas. These gas-phase data were correlated with the net effect of substrate processing for Si and ZrO2 surfaces. Surface-specific analyses were performed for post-processed substrates via x-ray photoelectron spectroscopy (XPS) and contact angle goniometry. Generally, precursors with lower F/C ratios tended to deposit robust FC films of high surface energy. Precursors of higher F/C ratio, such as CF4, were associated with etching or removal of material from surfaces. Nonetheless, a net balance between deposition of FC moieties and etching of material exists for each plasma system. The imaging of radicals interacting with surfaces (IRIS) technique provided insight into the phenomena occurring at the interface of the plasma gas-phase and substrate of interest. IRIS results demonstrate that CFx radicals scatter copiously, with surface scatter coefficients, S, generally greater than unity under most experimental conditions. Such considerable S values imply surface-mediated production of the CFx radicals at FC-passivated sites. It is inferred that the primary route to surface production of CFx arises from energetic ion bombardment and ablation of surface FC films. Other factors which may influence the observed CFx scatter coefficient include the surface with which the radical interacts, the vibrational temperature (ΘV) of the radical in its gas phase, and radical interactions in the gas phase. The analyses of ΘV in particular were extended to diatomic radicals from other plasma sources, including nitric oxide and fluorosilane systems, to gauge the contributions of vibrational energy to surface reactivity. In general, a monotonic increase in S is observed for CF, NO, and SiF radicals with increasing ΘV. Preliminary results for mixed plasma precursor systems (i.e. FC/H2, FC/O2) indicate that the choice of feed gas additives has a profound effect on surface modification. Hydrogen additions tend to promote FC film deposition through scavenging of fluorine atoms, whereas oxygen consumes polymerizing species, thus favoring etching regimes. Time-resolved optical emission spectroscopy (TR-OES) studies of gas-phase species elucidate the mechanisms by which these processes occur. Ultimately, the work presented herein expands the fundamental chemical and physical understanding of fluorocarbon plasma systems.Item Open Access Fast electronic driver for optical switches(Colorado State University. Libraries, 2012) Woolston, Mark R., author; Rocca, Jorge J., advisor; Marconi, Mario C., committee member; Menoni, Carmen S., committee member; Yalin, Azer P., committee memberElectronically controlled optical switches are critical components in many optical systems, including pulsed lasers. Solid-state optical switches based upon the Pockels effect are widely utilized in research and industry, however Pockels cells require electronic drivers capable of switching several kilovolts quickly and cleanly. This thesis reviews Pockels cell designs and their typical applications in laser systems, discusses common drive circuit topologies found in literature, and describes the development of a fast, stable electronic driver for half-wave congured Pockels cell optical switches. In a crowded optical environment, it is frequently desirable to locate the Pockels cell at some distance from the driver electronics. The driver was developed to be capable of 1.4 ns optical transition times when connected to a 6 pF Pockels cell via 1.2 meters of 50 ohm coaxial cable. The driver is designed to operate in colliding-pulse mode at 6-8 kV, with 80 ampere typical switch currents. Total switch propagation delay is less than 100 ns, and thermal drift has been measured at less than 50ps/C°. These pulsers are currently used to drive Pockels cells in colliding pulse mode in pulse picking and slicing applications where optical rise times of < 2 ns and low drift are needed. Novel non-invasive diagnostic techniques for measuring and graphing pulse propagation in a repeatable manner along collapsing avalanche transistor chains are presented.Item Open Access Iodine compatible hollow cathode(Colorado State University. Libraries, 2019) Thompson, Seth Joseph, author; Williams, John D., advisor; Farnell, Casey C., advisor; Yalin, Azer P., committee member; de la Venta Granda, Jose, committee memberMost electric propulsion (EP) systems utilize xenon gas as a propellant, which is expensive and must be stored in heavy high-pressure tanks, within which the storage density is still lower than desired. The halogen iodine (I2) has risen as a leading alternative propellant with the potential to overcome these drawbacks with its lower cost, higher storage density, and significantly reduced tank pressure. Hall-effect thrusters have been operated with iodine propellant in the range of a hundreds of watts to greater than ten kilowatts [1], [2], with performance comparable to that of devices operated on xenon; however, due to the reactive nature of iodine, the hollow cathode electron sources used with these thrusters, have been operated on xenon. Without being able to operate cathodes on iodine, the consideration of iodine propellant for many space missions is not possible. This research aims to develop and examine hollow cathode assemblies capable of operating on iodine propellant. We propose that a cathode can be constructed with iodine resistant materials and with an insert capable of participating in a tungsten-iodine life cycle that is utilized in halogen lamps to increase filament lifetime. Results from this work demonstrate that a cathode with a graphite tube and a tungsten-based ceramic-metal composite insert is capable of being operated on iodine for longer than any currently published operation time. This type of cathode has the potential to be operated on iodine for over 3,000 hours, a lifetime approaching the minimum requirement of EP systems currently being used.Item Open Access Relativistic plasma nano-photonics for ultra-high energy density physics(Colorado State University. Libraries, 2014) Purvis, Michael Anthony, author; Rocca, Jorge J., advisor; Yalin, Azer P., committee member; Menoni, Carmen S., committee member; Marconi, Mario C., committee memberThe trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays is shown to volumetrically heat near solid density matter transforming it into ultra-hot highly ionized plasmas. The plasmas were generated by focusing intense ~ 60 femtosecond duration ultra-high-contrast laser pulses onto targets consisting of arrays of densely packed vertically aligned nanowires 35-80 nm diameter. X-ray spectra are presented showing that irradiation of Ni and Au nanowire arrays heats a plasma volume several µm in depth to reach extraordinarily high degrees of ionization (i.e. 26 times ionized Ni , 52 times ionized Au), in the process generating gigabar level pressures. Electron densities nearly 100 times greater than the typical critical density and multi-keV temperatures are achieved using laser pulses of only 0.5 J energy. The large plasma volume and high electron density lead to an increased hydrodynamic-to-radiative lifetime ratio that results in a significant increase in X-ray yield. Measurements from a filtered photodiode array reveal a 100X increase in emission with respect to polished flat targets for photons with energies greater than 9keV. Scaling to higher laser intensities promises to create plasmas with temperatures and pressures approaching those in the center of the sun.