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Title: SEARCH FOR STERILE NEUTRINO OSCILLATIONS WITH THE PROSPECT EXPERIMENT
Creator: Surukuchi, Pranava Teja
Date: 2019
Description: Neutrinos have been one of the most interesting particles to study for the best part of the last century. Ever since the first discovery of...
Show moreNeutrinos have been one of the most interesting particles to study for the best part of the last century. Ever since the first discovery of neutrinos, various experiments using both natural and artificial neutrino sources have helped in determining the nature of neutrinos. In particular, experiments in the last two decades helped determine the neutrino oscillation parameters. Although three neutrino picture is well established, discrepancies have been observed in some recent reactor, accelerator, and source neutrino experiments hinting at the existence of a fourth weakly non-interacting neutrino called a sterile neutrino. Additional experimental investigation is needed to test the sterile neutrino hypothesis and identify the source of discrepancies. PROSPECT is a short-baseline reactor antineutrino experiment designed to search for sterile neutrinos and make a precise measurement of 235U reactor antineutrino spectrum from the High Flux Isotope Reactor at Oak Ridge National Laboratory located in Tennessee. The PROSPECT detector is segmented with 6Li-loaded liquid scintillator as the target. The design and development of the PROSPECT detector started in 2014 and the assembly and installation have finished by early 2018. PROSPECT detector has been collecting data since March 2018. The design, development, and installation of the detector is discussed with a particular emphasis on the components designed and developed at Illinois Institute of Technology. The detector calibration, event reconstruction, and data quality are also discussed. Finally, the sterile neutrino search using 33 days of reactor on data and 29 days of reactor off data is presented.
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Title: SPIN TRANSPORT AND SPIN-ORBIT TORQUES IN ANTIFERROMAGNETS
Creator: Saglam, Hilal
Date: 2019
Description: The electron has two fundamental degrees of freedom, i.e., charge and spin. Existing semiconductor electronics utilizes the charge degree of...
Show moreThe electron has two fundamental degrees of freedom, i.e., charge and spin. Existing semiconductor electronics utilizes the charge degree of freedom in its functionalities. Spintronics seeks, in addition, to exploit the spin degree of freedom, which can suggest promising pathways for low-power and faster operations. In conventional spintronics devices, ferromagnetic materials (FMs) have been employed as active components. However, it has recently been recognized that antiferromagnetic materials (AFMs) can also play an active role in spintronic devices. Antiferromagnets have several advantages over ferromagnets; for instance, they have net zero magnetization so that they are invisible to external magnetic fields. Also, they show resonances in the terahertz frequency range. Towards this end, this thesis focuses on spin transport and spin-orbit torques in various antiferromagnetic materials. With respect to the former, I demonstrated that spin currents can be transmitted efficiently through a metallic antiferromagnet FeMn. I detect two distinctly different spin transport regimes, which can be associated with electronic and magnonic spin currents. With respect to the latter, I investigated a possible correlation between two important spintronics concepts, i.e., spin-orbit torques and exchange bias since the ferromagnetic/antiferromagnetic interface is crucial for both phenomena. The measured spin Hall angles suggest that these two effects are independent of each other, although it is worthy to mention that there are still strong spin-orbit torques even when the antiferromagnet is directly exchange coupled to the ferromagnet. Furthermore, I discuss anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in another metallic antiferromagnet, FeRh, which undergoes a temperature driven antiferromagnetic-to-ferromagnetic phase transition. The temperature dependent results show a drastic suppression of both AHE and ANE signals in the antiferromagnetic phase. Interestingly, these non-vanishing signals are opposite in sign compared to their ferromagnetic counterparts, which can suggest changes of inherent symmetries in the electronic structure of FeRh across its magnetic phase transition.
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Title: Beam Line Design for Fully Staged Two Beam Acceleration at the Argonne Wakefield Accelerator Facility
Creator: Neveu, Nicole
Date: 2018
Description: Two beam acceleration (TBA) is a candidate for future high energy physics machines and FEL user facilities. This is a scheme in which an...
Show moreTwo beam acceleration (TBA) is a candidate for future high energy physics machines and FEL user facilities. This is a scheme in which an electron accelerator uses a ``drive'' beam to transport and supply the RF power needed for acceleration on a secondary and independent 'witness' accelerator. This technology is attractive for its potential to improve the efficiency and simplicity of large scale machines. At the Argonne Wakefield Accelerator Facility (AWA), research into this potential accelerator scheme is ongoing. Completed experiments include a simplified staging set up, where high-charge, 65 MeV drive bunch trains were injected from the RF photoinjector into decelerating structures to generate a few hundred MW's of RF power. This RF power was transferred through an RF waveguide to accelerating structures that were used to accelerate the witness beam. Staging refers to the sequential acceleration (energy gain) in two or more structures on the witness beam line. The main limitation in past experiments was difficulty achieving 100\% transmission in the second stage which resulted in lower power generation. AWA plans to demonstrate fully staged TBA, which requires a separate beam line for each decelerating/accelerating pair. In this thesis, design specifications and initial hardware tests needed for a new, independent beam line for TBA was done. Simulations of the drive line were done using the code OPAL. Since OPAL was new to the AWA group, a benchmark comparison with ASTRA and GPT was done to validate initial results. Then two optimization algorithms were investigated and used to optimize the drive line at 40 nC. Comparison of results between the two algorithms were done, with no major discrepancies found. Then large scale and parallel optimizations were done for the optics configuration in the fully staged TBA beam line design. A kicker was designed and incorporated into the drive beam line to accomplish a modular design so that each accelerating structure can be independently powered by a separate drive beam. Experimental measurements of the kicker indicate the angle increases linearly with the supplied voltage, and the angle achieved meets the design requirements for fully staged TBA. Optics optimization was done to minimize the beam size at the center of the decelerating structures to ensure good charge transmission. The resulting design will be the basis for proof of principle experiments that will take place at the AWA facility.
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Title: Structural Studies of Degradation Mechanism of Lithium Rich Manganese, Nickel, and Iron Based Cathodes
Creator: Aryal, Shankar
Date: 2018
Description: Layered oxide compounds are superior with respect to discharge voltage and discharge specific capacity compared to other families of cathodes....
Show moreLayered oxide compounds are superior with respect to discharge voltage and discharge specific capacity compared to other families of cathodes. Therefore, LiCoO2 and LiMnxNiyCozO2, are the most commonly used cathodes since the commercialization of lithium ion battery. Recently, Li rich Ni, Mn, and Co oxide composite cathodes have been introduced with some improvements. As Co is toxic and expensive, attempts have been made to replace Co with cheap and environmentally friendly Fe. This dissertation reports that comparable discharge specific capacity and discharge voltage can be achieved by replacing Co with Fe and optimizing the composition of Mn, Ni, and Fe. However, the capacity and voltage fading on cycling are still remaining challenges. Structural change on electrochemical cycling is the main reason behind this fading. X-ray absorption spectroscopy (XAS), the specific element probe technique to study local structure and X-ray diffraction (XRD) to study the crystallographic phase information are utilized to understand the degradation/aging mechanism. A series of Li rich Mn, Ni, and Fe oxide composite cathode materials Li1.2Mn(0.30+x)Ni(0.40-x)Fe0.10O2 for x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25 were prepared using a sol-gel synthesis method. Rhombohedral and monoclinic crystal phases are found in Li rich Mn, Ni, and Fe composite oxide materials, but pure rhombohedral phase cannot be obtained without excess Li in the stoichiometric LiMO2 form. The pure monoclinic phase Li2MnO3 is also synthesized to confirm its presence in the composite oxide cathodes. Particle size and surface morphology are studied with scanning electron microscopy. The composite cathodes are cycled to over 100 cycles at 0.3C, for C = 250 mAhg-1 rate. XAS before and after 100 electrochemical cycles of Li rich Mn-Ni-Fe based cathodes is reported for the first time. The determination of fractional contents of monoclinic and rhombohedral phases in the composite oxide cathodes is not possible by powder XRD analysis, however, Li2MnO3 content decreases on decreasing Mn content and on increasing Ni content. The composition with higher Ni content has a higher degree of cation mixing. The synergistic effect of rhombohedral and monoclinic phases in Li rich Mn, Ni, and Fe based cathode is critical for stable electrochemical performance. The Li1.2Mn0.50Ni0.20Fe0.10O2 cathode showed the most stable cyclability performance (194 mAhg-1 first discharge capacity with 94 % capacity retention after 100 cycles at 0.3C rate) however, Li1.2Mn0.40Ni0.30Fe0.10O2 (220 mAhg-1 first discharge capacity with 57 % capacity retention) and Li1.2Mn0.55Ni0.15Fe0.10O2 (241 mAhg-1 first discharge capacity with 68 % capacity retention) cathodes showed higher 1st discharge capacity but poor cyclability under the same charge/discharge cycling.The XAS at Mn K-edge is used to explain the mechanism of Li2MnO3 activation for the improved electrochemical performance of Li rich Mn, Ni, and Fe oxide composite cathode, however Li2MnO3 contributed differently in different compositions. Synchrotron XRD and XAS measurements probed the lattice size expansion, which decreases the chemical potential of Li ions in the cathode on cycling leading to lower discharge voltage after cycling.
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Title: A Novel Non-parametric Density Estimation Approach to Measuring Muon Ionization Cooling and Reverse Emittance Exchange in the MICE Experiment
Creator: Mohayai, Tanaz Angelina
Date: 2018
Description: The Muon Ionization Cooling Experiment (MICE) located at Rutherford Appleton Laboratory in the U.K. has demonstrated muon ionization beam...
Show moreThe Muon Ionization Cooling Experiment (MICE) located at Rutherford Appleton Laboratory in the U.K. has demonstrated muon ionization beam cooling for the first time. A beam of muons in MICE is produced from high-energy proton beam collision with a fixed target, generating pions which in turn decay into muons. Pion-decay muons, thus, are tertiary particles and, as a result, occupy a large volume in position‒momentum phase space. To fit the muon beam into smaller and more cost-effective accelerating devices, muon beam phase‒space volume needs to be reduced (beam cooling). Ionization beam cooling, which before MICE has never been demonstrated experimentally for muons, is the only technique fast enough to be used for muons within their short lifetime. Ionization cooling occurs when muons traverse an absorbing material and lose momentum through ionization energy loss. The cooling effect in MICE is measured using two scintillating-fiber tracking detectors. These trackers, one upstream and one downstream of the absorber, reconstruct and measure the position and momentum coordinates of each muon. Given the precision MICE needed to demonstrate beam cooling, it is necessary to develop analysis tools that can account for any effects that may lead to inaccurate measurement of cooling, such as non‒linear effects in beam optics. Non‒parametric density estimation techniques, such as kernel density estimation (KDE), provide a basis for creating analysis tools that are robust against these effects, directly calculating the muon beam phase-space density and volume for demonstrating beam cooling. This thesis focuses on the application of KDE to the measurement of beam cooling in MICE. The KDE technique is validated using known distributions and is applied to simulated and experimental MICE data corresponding to the various magnet, optics, and absorber configurations. Using the KDE technique, muon beam cooling in the four‒dimensional transverse phase space, as well as reverse emittance exchange using MICE data have been demonstrated.
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Title: INVESTIGATION OF STRUCTURE AND PROCESSING EFFECTS ON THE ELECTROCHEMICAL PERFORMANCE OF COBALT-FREE, LITHIUM- AND MANGANESE-RICH LAYERED OXIDE CATHODE FOR LIBS
Creator: Kucuk, Kamil
Date: 2021
Description: Rechargeable Li-ion batteries (LIBs) have been widely used in a diverse range of energy storage systems because of their high energy and power...
Show moreRechargeable Li-ion batteries (LIBs) have been widely used in a diverse range of energy storage systems because of their high energy and power density, low self-discharge, and tolerable memory effect, compared to the conventional alkaline, lead acid, and nickel-cadmium (Ni/Cd) batteries. [2] Since not only cathodes materials control the energy density of a cell, but also the capacity of cathode material characteristically restricts the cell capacity (as well as about 40% of the cell cost results from the cost of cathode raw materials), the majority of studies on LIBs have been carried out on developing alternative cathodes with higher energy, lower cost, and more environmentally friendliness. [2], [3] From this perspective, both Co-free and lithium- & manganese-rich (LMRO) layered oxide MNF cathodes, Li1.2(MnxNiyFez)O2, have recently attracted great attention in lithium-ion battery (LIB) research for electric vehicles and energy storage devices due to their high capacities of over 250 mAhg−1 and being eco-friendly and inexpensive compared to the cobalt-based Li-rich Li1.2(NixMnyCoz)O2 and Ni-rich Li(NixMnyCoz)O2 (NMC), and LiCoO2 commercial cathodes. Replacing toxic and expensive Co in the LMRO cathodes with environmentally friendly and much cheaper Fe element has been extensively studied over the last two decades. It was suggested by Aryal, S. et. al., in 2018. [4] that the Li1.2(Mn0.50Ni0.20Fe0.10)O2 (MNF502010) Co-free LMRO MNF cathodes seem better in terms of capacity-retention with higher discharge capacity and less voltage fade compared to other MNF compositions. However, the MNF502010 cathode still suffers from its lower experimental capacity, compared to its expected theoretical capacity (270-455 mAhg−1), as well as capacity decay, voltage fade, poor rate capability, and thermal instability. In this dissertation, it is reported that comparable specific discharge capacity with less amount of voltage fading and capacity decay can be achieved by fluorine doping, synthesizing materials in large amounts (0.1 mol synthesis at least) with two-step firing, and then washing the obtained nanocomposites with H3PO4 to create Li3PO4 layer on the surface of bulk MNF composites. The specific discharge capacity and cycling performance of the Co-free MNF502010 cathodes were studied and enhanced by using and optimizing these approaches in this work for the first time. However, voltage fading and capacity decay are still remaining challenges, even if they are remarkably mitigated by applying these approaches. Structural changes due to layered to spinel transformation, less amount of monoclinic phase activation leading to structural deformation occurring after 1st charge, dissolution of the transition metals (TM), and oxygen release (loss of lattice oxygen) from the MNF material upon following electrochemical cycling at higher voltage (≥ 4.5V ) seem the main reasons behind these challenges, specifically the voltage fading and capacity decay.A series of fluorine-doped/undoped, Co-free MNF502010 nanocomposite cathode materials (Li1.2(Mn0.50Ni0.20Fe0.10)O2(1−x)F2x, briefly F-doped MNF) were synthesized by using a sol-gel technique. Firstly (Chapter 4), the fluorine was substituted for oxygen in the parent MNF compound in different fractions (0.00, 0.025, 0.05,0.075, 0.10, which means 0%, 2.5%, 5.0%, 7.5%, and 10%), in order to optimize the amount of fluorine for better performance; secondly (Chapter 5), a large batch (0.1mol, 10 times more than the previous batch) of 5%F-doped material was prepared by a modified sol-gel synthesis which is modified by heating at 700 ◦C for different time-periods; 7.5 hours (7.5h), 15 hours (15h, two-step firing, 7.5h + rest for 12h + 7.5h), instead of heating directly 15 hours (d15h), as done in the first chapter; finally (Chapter 6), H3PO4 treatment resulting in a non-uniform Li3PO4 layer on the bulk surface. These approaches were respectively applied on doped/undoped MNF502010 nano-composites, in order to overcome the challenges already mentioned above. Finally, the effects of these approaches on the structural, morphological, and electrochemical properties of MNF cathode materials were investigated by means of powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray (EDS) analysis, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge-discharge cycling, and X-ray absorption spectroscopy (XAS, an element specific probe technique). Specifically, ex-situ XAS was performed at the Mn, Ni, and Fe K-edge and used to detect the changes both in the oxidation state of the transition metal (TM) ions and their local environments in order to get a better understanding of the improved performance of the composite materials, as well as their failure mechanism. Moreover, the EXAFS data were modeled to gain insight into the influence of these approaches on the electrochemical performance of both pristine (uncycled) and cycled electrodes (after the 100th discharge). From correlating the electrochemical performance of the modified/unmodified MNF nano-composite cathodes to their XANES and EXAFS analysis, the ability to achieve higher specific capacity is strongly dependent on the formation of a well-ordered layered structure and the amount of monoclinic component (Li2MnO3) activation resulting in higher redox-activity of the Mn cations. The long-term cyclability or capacity retention can be enhanced by heating the resulting powders with a two-step firing (instead of directly 15 hours) and washing them with 1wt%H3PO4 solution to create a Li3PO4 conductive and protective layer.
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Title: FIELD EMISSION MITIGATION VIA IN-SITU PLASMA PROCESSING IN 1.3 GIGAHERTZ 9-CELL LCLS-II CAVITIES
Creator: Giaccone, Bianca
Date: 2021
Description: Field emission (FE) is one of the limiting factors in superconducting radiofrequency cavities' performance. It is known that even a few...
Show moreField emission (FE) is one of the limiting factors in superconducting radiofrequency cavities' performance. It is known that even a few monolayers of surface adsorbed contaminants can lower the niobium work function and increase the FE. In order to address the field emission that may arise once the accelerator is already assembled, it was decided to develop plasma processing for the Linac Coherent Light Source II, a method to mitigate field emission in-situ. Starting from Doleans's successful experience with plasma processing for high beta cavities, Fermi National Accelerator Laboratory is developing plasma cleaning for TESLA shaped 1.3 GHz 9-cell cavities. A new method of ignition based on the higher order modes and couplers was developed, along with a detection procedure that allows to identify the location of the plasma inside the cavity. In this work are presented the results of plasma processing applied to 1.3 GHz cavities, both single-cell and 9-cells. The cavities were contaminated with multiple sources, naturally or artificially, and their performance was measured through cryogenic RF tests before and after plasma cleaning. These experiments proved that plasma processing successfully removed hydrocarbon-related field emission from cavities artificially contaminated, but also from a cavity with natural and unknown FE source. In some cases of more extreme contamination through vacuum failure simulation conducted in air (not in a cleanroom), plasma processing was not able to recover the cavity's performance. An ongoing analysis of the cavity contaminants is presented here, explaining the reason why some contaminated cavities showed little improvement after plasma processing. A microscopic study of the effect of plasma processing on the niobium surface is also presented. Niobium samples prepared with different surface treatments were analyzed using X-ray photoelectron spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The samples were subjected to plasma processing and analyzed again, in order to draw a comparison and identify possible surface changes caused by the reactive oxygen contained in the glow discharge. The samples were prepared with different surface treatments in order to understand if plasma processing may affect them differently. This study showed a possible increase in the oxide thickness after plasma processing and a reduction of the energy difference between the pentoxide and the metal peaks. In preparation for this study, the near-surface region of one niobium sample was investigated with X-ray photoelectron spectroscopy at various steps of sputtering and subsequent oxide regrowth in air. The results showed that the majority of the oxide is composed of Nb2O5, however, the presence of two suboxides (NbO, NbO2) is observed, plus an additional peak (attributed to Nb2O) measured both during sputtering and oxide regrowth.
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Title: Electron Cloud studies at Fermilab
Creator: Ji, Yichen
Date: 2019
Description: The presence of unwanted electrons in an accelerator vacuum chamber, known as E-cloud (E-cloud) can potentially cause operational problems in...
Show moreThe presence of unwanted electrons in an accelerator vacuum chamber, known as E-cloud (E-cloud) can potentially cause operational problems in the Fermilab Main Injector (MI) and Recycler Ring (RR). E-cloud has caused instability in the RR in the past, and although it is not currently a problem, there is measurable E-cloud in the MI accelerator. There are planned beam intensity increases due to upgrades of the Fermilab accelerator complex, so E-cloud could become a problem. Some work has been done by others previously to understand how low SEY (Secondary Electron Yield coefficient) coatings might mitigate production of E-cloud, and to model the mechanism whereby E-cloud causes beam instability. Using previous studies as a base, this research took several approaches toward understanding the risk of E-cloud at Fermilab. The evolution of the SEY of the SS316L (stainless steel), TiN coated SS316L, and amorphous carbon coated SS316L were measured in-situ using a SEY measurement station in the MI tunnel. The SEY of these materials change over time either due to bombardment of the E-cloud, or disruption of vacuum conditions. The SEY evolution was tracked over a several year period to find out how long it takes for the SEY of each material to reach its lowest level, and how much the SEY rises during deconditioning periods of poor vacuum. The SEY measurement results can be used to determine whether the SS316L will be a problem at upgrade intensities, and if so, whether or not TiN and A-Carbon coatings can mitigate E-cloud related problems sufficiently. Direct measurements of the E-cloud were done as well, and compared to simulation. The E-cloud bombardment rate was measured at different beam intensities and bunch lengths. It was possible to get detailed information on how the E-cloud varies over the acceleration cycle, where sensitivity to bunch length is reflected in the evolution of the E-cloud. The Retarding Field Analyzer (RFA) measuring the E-cloud bombardment rate was near the instrument that is used to measure the SEY of the beam pipe material. This proximity provided an accurate SEY value for simulations, so that the simulated E-cloud bombardment rate could be better compared to measurement. Bunch length measurements and computations generated accurate bunch length information also needed as input for simulations. After this careful control of the input parameters, the POSINST simulations of E-cloud were a good match to direct measurements. This gave confidence that predictions could be made concerning the E-cloud densities at upgrade intensities. These densities were compared against corresponding proton densities to predict the SEY required to avoid instabilities. That prediction and the information provided by the SEY measurements provide helpful information regarding the risks of E-cloud effects at future beam intensities at Fermilab.
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Title: IN SITU X-RAY ABSORPTION SPECTROSCOPY STUDY OF TIN-BASED GRAPHITE COMPOSITE ANODES FOR LITHIUM-ION BATTERIES
Creator: Ding, Yujia
Date: 2019
Description: Sn-based anode materials such as Sn, SnO2, Sn4P3, and SnS2 that exhibit large theoretical capacities are promising alternatives to traditional...
Show moreSn-based anode materials such as Sn, SnO2, Sn4P3, and SnS2 that exhibit large theoretical capacities are promising alternatives to traditional graphite anodes for Li-ion batteries. However, their capacities fade drastically in a few cycles due to substantial volume changes during the lithiation/delithiation process resulting in cracking and pulverization of the electrode. A graphite matrix is introduced by high-energy ball milling to obtain a graphite composite and enhance the electrochemical performance. Indeed, Sn4P3/graphite composite exhibits a reversible capacity of 651 mA h g-1 in the 100th cycle, and SnS2/graphite composite shows 591 mA h g-1 in the 50th cycle.To obtain a better understanding of the improved performance of the composite materials and the reason for the more gradual capacity fading, in situ EXAFS is used to investigate these mechanisms using in situ coin cells and in situ vacuum-sealed pouch cells. The collected EXAFS data were analyzed by modeling to extract detailed local environment changes during the lithiation/delithiation process.In the crystalline phases of Sn-based materials, the conversion reaction forming metallic Sn is partially reversible and partially irreversible, and the subsequent alloying/dealloying reaction forming LiSn alloys is reversible. Introducing the graphite matrix increases electrical conductivity and prevents aggregation of intermediate Sn clusters. The graphite matrix also plays a significant role in transforming composites into highly dispersed amorphous phases. These amorphous phases, formed in the first few cycles of Sn4P3/graphite and SnS2/graphite composites, exhibit excellent reversibility in both conversion and alloying/dealloying reactions, which is the main reason for the significant improvements in electrochemical performance. The slow growth of metallic Sn clusters and the slight reduction in amorphous phases result in gradual capacity loss over long-term cycling. Introducing the graphite matrix and creating highly dispersed composite samples are the successful strategies that can be scaled up to develop new battery materials in the future.
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Title: Advanced methods for storage ring nonlinear beam dynamics design and implementation
Creator: Song, Minghao
Date: 2022
Description: To meet the increasing demands of scientific researchers for brighter photonbeams, storage ring beam emittance is continually pushed down to a...
Show moreTo meet the increasing demands of scientific researchers for brighter photonbeams, storage ring beam emittance is continually pushed down to a new ultra-low level. It, therefore, becomes correspondingly more challenging to ensure such storage rings have good nonlinear beam dynamics performance. This thesis work is focused on developing advanced methods for low emittance storage ring nonlinear beam dynamics design and implementation.Nonlinear beam dynamics optimization is essential to low emittance storagering design. A highly efficient multi-objective optimization algorithm is needed to simultaneously achieve a large dynamic aperture and a large local momentum aperture. Work was done to improve and test a machine learning-based algorithm called multi-generation Gaussian process optimizer (MG-GPO). This advanced method uses constructed GP models to pre-select solutions, and benchmarking of results on toy problems shows that MG-GPO converges significantly faster than traditional algorithms. The MG-GPO algorithm was successfully applied to nonlinear lattice design optimization, for example, to the SPEAR3 upgrade 7-nm lattice, and it was demonstrated to converge faster than NSGA-II and MOPSO. This was due to its capability of selecting candidates that tend to have better performance. This algorithm will help accelerate nonlinear lattice studies.Correction of nonlinear beam dynamics is also important for low emittancestorage ring commissioning and operation. In order to measure and correct features relevant to the nonlinear beam dynamics, an effective method is needed to excite sustained beam oscillations to large amplitude. A method based on the concept of autoresonance was proposed. This advanced technique excites nonlinear transverse beam motion in storage rings by sweeping the drive frequency. The theory for the autoresonance threshold was derived for the nonlinear optics systems in storage rings, both with and without damping effects, using Hamiltonian dynamics. The theoretical predictions for the drive amplitude threshold were found to agree well with simulations for a simple storage ring model, as well as for simulations with the actual SPEAR3 and APS lattices. The theory was also compared favorably to historical data from experiments on SPEAR3. Simulations verified that an oscillation driven by autoresonant excitation matches the character of a free oscillation, so that beam oscillation data taken during the ramping process can confidently be used to characterize the nonlinear beam dynamics performance. The precision of measurements can be improved by using autoresonant excitation since large amplitude beam oscillations are sustained significantly longer. Simulations of autoresonant excitation demonstrated the measurements of the detuning coefficients and resonance driving terms. The use of autoresonant excitation for the detection of faulty magnets and correction of resonance driving terms was also demonstrated.Online optimization is an alternative way to effectively improve nonlinear beamdynamics performance in a real storage ring. The greater efficiency of an advanced optimization algorithm is also needed to find globally optimal solutions in the limited experimental time that is typically available. The MG-GPO algorithm was implemented for SPEAR3 vertical emittance minimization and injection efficiency optimization. Again, the optimized solutions demonstrate that MG-GPO is more efficient than the commonly used PSO algorithm. SPEAR3 performance was successfully improved during the online optimization runs with MG-GPO.
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Title: MEASUREMENT OF ELECTRON NEUTRINO AND ANTINEUTRINO APPEARANCE WITH THE NOνA EXPERIMENT
Creator: Yu, Shiqi
Date: 2020
Description: As a long-baseline neutrino oscillation experiment, the NuMI Off-axis $\nu_e$ Appearance (NOvA) experiment aims at studying neutrino physics...
Show moreAs a long-baseline neutrino oscillation experiment, the NuMI Off-axis $\nu_e$ Appearance (NOvA) experiment aims at studying neutrino physics by measuring neutrino oscillation parameters using the neutrino flux from the Main Injector (NuMI) beam. It has two functionally identical detectors. The near detector is onsite at Fermi National Accelerator Laboratory. The far detector is 810 km away from the source of neutrinos and antineutrinos, at Ash River, Minnesota. At the near detector, muon neutrinos or antineutrinos, before significant oscillations take place, are used to correct the Monte Carlo simulation. At the far detector, the neutrino and antineutrino fluxes after significant oscillations have happened are measured and analyzed to study neutrino oscillation. The NOvA experiment is sensitive to the values of $\sin^2\theta_{23}$, $\Delta m^2_{32}$, and $\delta_{CP}$. The latest values from the NOvA 2020 analysis are as follows: $\sin^2\theta_{23}=0.57^{+0.03}_{-0.04}$, $\Delta m^2_{32}=(2.41\pm0.07)\times10^{-3}$ eV$^2$/c$^4$, and $\delta_{CP}=0.82\pi$ with a wide 1$\sigma$ interval of uncertainty. My study is focused on the neutrino oscillation analysis with NOvA, including detector light model tuning, particle classification with convolutional neural network, electron neutrino and antineutrino energy reconstruction, and oscillation background estimation. Most of my studies have been used in the latest NOvA publication and the NOvA 2020 analysis.
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Title: Development of a novel ultra-nanocrystalline diamond (UNCD) based photocathode and exploration of its emission mechanisms
Creator: Chen, Gongxiaohui
Date: 2020
Description: High quality electron sources are one of the most commonly used probing tools used for the study of materials. Photoemission cathodes, capable...
Show moreHigh quality electron sources are one of the most commonly used probing tools used for the study of materials. Photoemission cathodes, capable of producing ultra-short and ultra-high intensity beams, are a key component of accelerator based light sources and some microscopy tools. High quantum efficiency (QE), low intrinsic emittance, and long lifetime (or good vacuum tolerance) are three of the most critical features for a photocathode; however, these are difficult to achieve simultaneously and trade-offs need to be made for different applications. In this work, a novel semi-metallic material of nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) has been studied as a photocathode. (N)UNCD has many of the unique diamond properties, such as low intrinsic as-grown surface roughness (at the order of 10~nm) due to its nanometer scale crystalline size, relatively long lifetime in air, high electrical conductivity with nitrogen doping, and potentially high QE performance due to the high grain boundary densities where most of electron emission occurs. High contrast interference of incident and reflected radiation within (N)UNCD thin films was observed, and this feature allows fast thickness determination based on an analytical optics methodology. This method has been extended to study and calculate the etching rates of two commonly used O$_2$ and H$_2$ plasmas for use with future (N)UNCD microfabrication processes. The mean transverse energy (MTE) of (N)UNCD was determined over a wide UV range in a DC photogun. Unique MTE behavior was observed; it did not scale with photon energy unlike most metals. This behavior is associated with emission from spatially-confined states in the graphite regions (with low electron effective mass) between the diamond grains. Such behavior suggests that beam brightness many be increased by the simple mechanism of increasing the photon energy so that the QE increases, while the MTE remains constant.Two individual (N)UNCD photocathodes synthesized two years apart have been characterized in a realistic RF photogun. Both the QE and intrinsic emittance were characterized. It was found that the QE of $\sim4.0\times 10^{-4}$, is more than an order of magnitude higher than that of most commonly used metal cathodes (such as Cu and Nb). The intrinsic emittance (0.997~$\mu$m/mm) is comparable to that of photocathodes now deployed in research accelerators. The most impressive feature is the excellent robustness of (N)UNCD material; there was no evidence of performance degradation, even after years-long atmospheric exposure. The results of this work demonstrate that a cathode made of (N)UNCD material is able to achieve balanced performance of three of the primary critical photocathode figures-of-merit.
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Title: An Alternative Approach for the Jefferson Lab Electron-Ion Collider Ion Accelerator Complex
Creator: Martinez Marin, Jose Luis
Date: 2020
Description: An assessment by the National Academy of Sciences (NAS) of the scientific merit for a future Electron Ion Collider (EIC) in the US concluded...
Show moreAn assessment by the National Academy of Sciences (NAS) of the scientific merit for a future Electron Ion Collider (EIC) in the US concluded that such a facility would be unique in the world and enable indispensable research on current and compelling scientific questions. This assessment confirmed the recommendations of the 2015 Nuclear Science Advisory Committee (NSAC) for an EIC with highly polarized beams of electrons and ions, sufficient luminosity and sufficient, variable center-of-mass energy. Proposals were requested for a cost-effective design that uses existing accelerator infrastructure to reduce the risk; one of two major proposals submitted for consideration originated from the Thomas Jefferson National Accelerator Facility (JLab). The Jefferson Laboratory Electron-Ion Collider (JLEIC) would use the Continuous Electron Beam Accelerator Facility (CEBAF) at JLab as a full-energy electron injector. The primary accelerator challenges are twofold: producing and maintaining a high degree of polarization for both beams, and achieving high luminosity. This thesis project was part of an effort to produce an alternative, low-risk and cost- effective design for the JLEIC ion complex. The primary goal was not to find a replacement for the JLEIC ion complex design, but rather to investigate alternative options for the different components of the ion complex that could lower the overall cost, reduce its footprint, mitigate risk, and identify possible staging or future upgrades of the project. The platform for this thesis was the alternative design for the JLEIC ion complex that included (1) a more compact ion linac, (2) two staged ion boosters instead of one before injection to the collider ring, with a more compact and lower energy Pre-Booster ring as the first stage, and (3) the dual use of the electron storage ring (e-ring) as a second stage ion Large Booster.The alternative design was first investigated for medium energy (65-GeV center-of-mass), and was then upgraded following the National Academy of Sciences (NAS) review to higher energy (100-GeV center-of-mass). Developing a more cost-effective design and meeting all the requirements is challenging due to several constraints imposed on the alternative approach -- for example, the use of only room-temperature magnets for both ion boosters. There are also space limitations, the need to keep the shape and crossing angle of the ion Large Booster the same as the collider ring, ensuring reasonable length and aperture requirements for the magnets, and avoiding transition crossing for all the rings, which can cause beam dilution and instabilities.Development of both the Medium-Energy and the High-Energy options is presented. The Medium-Energy option consists of a 135 MeV injector linac, a 3 GeV octagonally-shaped Pre-Booster ring and a 11 GeV Large Booster. The High-Energy option consists of a 150 MeV (~ 40 MeV/u for Pb) injector linac, a 8 GeV (~ 2.04 GeV/u for Pb) non figure-8 Pre-Booster ring and a 40 GeV proton (~ 16 GeV/u for Pb) Large Booster, which would also serve as the electron storage ring (e-ring). The figure-8 shape of the Large Booster helps to maintain high polarization. High luminosity is achieved following a strategy to have a high bunch repetition rate of the colliding beams, very short bunch lengths, and small transverse emittances; the main concern here is to provide a lattice that is consistent with these requirements. The main results reported are the lattice design optimization and consolidation, benchmarking of the beam optics with different codes such as ELEGANT, COSY-Infinity, MAD-X, TRACE-3D, and Zgoubi, and spin resonance simulation results. Spin dynamics studies were performed for the linac and the Pre-Booster, and mechanisms to preserve the polarization are proposed. Beam formation and non-linear effects such as chromaticity, space charge, and intra-beam scattering were also studied to gain understanding of how the alternative approach could affect the baseline beam formation scheme and to ensure that the beam requirements are met through the injector chain with this alternative approach. It was shown that the polarization can be preserved through the alternative ion complex even with the more compact linac and a Pre-Booster that does not have a figure-8 shape by using a sufficiently long spin correction solenoid in the linac and a partial Siberian snake in the Pre-Booster. The baseline beam formation scheme could still be used to reach the required beam characteristics for collider injection. Cooling is not needed in the more compact Pre-Booster, and the large, higher energy booster helps to avoid space charge effects at extraction. This study has confirmed the effectiveness of the alternative approach as concerns the optics, acceleration, polarization, and beam formation. The ion injectors are sufficiently compact, and the ion Large Booster size and shape are consistent with the e-ring requirements, enabling the desired dual functionality of that machine. This work created a basis for design discussions during the JLEIC design process. The final High-Energy design for the JLEIC ion complex adopted design features that came from the alternative design studies, which were derived in part from this work—in particular, the shorter, lower-energy linac, the use of two boosters in the injection chain before the collider ring, and the ability to have only room-temperature magnets in the boosters, with superconducting magnets used only in for the collider ring.
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