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Title: NEUTRON PRODUCTION IN THE M2 MUON BEAM LINE AT CERN
Creator: Draeger, Emily
Date: 2014, 2014-05
Description: Spallation neutrons produced from cosmic ray muons are a major source of backgrounds in underground physics experiments. Experiments have been...
Show moreSpallation neutrons produced from cosmic ray muons are a major source of backgrounds in underground physics experiments. Experiments have been done to study spallation neutron production and yield, but our understanding of these processes is still limited. There are various interactions that can produce spallation neutrons. Most of these production mechanisms are fairly well understood; much of the uncertainty in our understanding of spallation neutrons lies in mechanisms such as virtual photon exchange and the assumptions used to calculate the photonuclear cross section. Even the experiments that have been carried out do not agree with each other or theoretical calculations. Spallation neutron production mechanisms are discussed, as well as a new experiment to study spallation neutrons. The impact of this study on current and future underground physics experiments is also explored.
PH.D in Physics, May 2014
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Title: DEVELOPMENT OF A HIGH ANGULAR RESOLUTION DIFFUSION IMAGING TEMPLATE AND PROBABILISTIC CONNECTIVITY-BASED ATLAS OF THE HUMAN BRAIN
Creator: Varentsova, Anna
Date: 2016, 2016-05
Description: Digital human brain atlases consisting of MRI-based templates and semantic labels delineating different brain regions serve a critical role in...
Show moreDigital human brain atlases consisting of MRI-based templates and semantic labels delineating different brain regions serve a critical role in neuroimaging, mainly facilitating spatial normalization and automated segmentation for the purposes of voxel-wise, region-of-interest, and network analyses. Diffusion MRI templates contain rich information about the microstructure of the brain, however the accuracy of templates constructed based on the diffusion tensor imaging (DTI) model is limited in regions with complex neuronal microarchitecture. High angular resolution diffusion imaging (HARDI) overcomes limitations of the DTI model and is capable of resolving intravoxel heterogeneity. In this work a method to develop artifact-free HARDI template of the human brain from low angular resolution data is presented. Existing white matter (WM) atlases have been generated either based on anatomical landmarks, thus mixing tracts with substantially different roles, or using DTI tractography, which fails in regions with crossing fibers. Connectivity-based atlases developed using HARDI templates and probabilistic tractography have potential to identify functionally distinct subregions of the brain. This work presents connectivity-based atlas of human brain WM created using HARDI template in ICBM-152 space and a set of FreeSurfer grey matter labels.
Ph.D. in Physics, May 2016
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Title: FIELD AND PHOTO-EMISSION IN A SHORT-PULSE, HIGH-CHARGE CESIUM TELLURIDE RF PHOTOINJECTOR
Creator: Wisniewski, Eric E.
Date: 2014, 2014-05
Description: A new high-charge RF gun is now operating at the Argonne Wakefield Accelerator (AWA) facility at Argonne National Laboratory (ANL). The 1.5...
Show moreA new high-charge RF gun is now operating at the Argonne Wakefield Accelerator (AWA) facility at Argonne National Laboratory (ANL). The 1.5 cell 1.3 GHz gun uses a Cesium telluride photocathode driven with a 248 nm laser to provide short-pulse, high charge electron beams for the new 75 MeV drive beamline. The high-gradient RF gun (peak field on the cathode > 80MV/m) is a key piece of the facility upgrade. The large Cs2Te photocathode (diameter > 30 mm) was fabricated in-house. The photo-injector will be used to generate high-charge, short pulse, single bunches (Q > 100 nC) and bunch-trains (Q>1000 nC) for wakefield experiments, typically involving dielectric-loaded accelerating structures. Details of the photocathode fabrication process and the results of associated diagnostic measurements are presented, including QE measurements and work function measurements performed with a Kelvin probe. Field-emitted dark current from the Cs2Te cathode was measured during RF conditioning and characterized. Fowler-Nordheim plots of the data are presented and compared to similar measurements made using a copper cathode in the initial phase of conditioning. The results for cesium telluride exhibited non-linear regions within the Fowler-Nordheim plots similar to previous experimental results for other p-type semiconductors. Results of quantum efficiency (QE) studies are presented with the cathode operating in both single and bunch-train modes. QE uniformity and lifetime studies are presented. During commissioning, the cesium telluride photocathode produced bunch-charge of 100 nC, breaking the previous record. No evidence of bunch-train position-dependence of QE was found when generating four-bunch trains with total charge up to 200 nC.
PH.D in Physics, May 2014
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Title: ELIASHBERG ANALYSIS OF CUPRATE OXIDE SUPERCONDUCTORS
Creator: Ahmadi, Omid
Date: 2011-11, 2011-12
Description: In this thesis, evidence for antiferromagnetic spin uctuations as the pairing glue in high temperature superconductors is presented through a...
Show moreIn this thesis, evidence for antiferromagnetic spin uctuations as the pairing glue in high temperature superconductors is presented through a modi ed Eliashberg analysis of experimental tunneling data of Bi2212 over a wide range of doping. In particular, the normalized conductance data of the junctions, from optimal to overdoped, will be tted at T=0K using d-wave Eliashberg equations where the spectral function is modeled after spin uctuation spectra seen in experiments. The corresponding real and imaginary diagonal and anomalous self-energy curves are extracted and compare well to photoemission experiments. This is followed by a temperature dependent Eliashberg analysis where the spectral function is now temperature dependent, based on trends seen in inelastic neutron scattering experiments. New results for temperature dependent self energy curves are also compared to experiment with slight deviations. Finally, the Josephson product is calculated as an independent check of the tunneling matrix used in tting the data.
Ph.D. in Physics, December 2011
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Title: NEW TOOLS FOR JET ANALYSIS IN HIGH ENERGY COLLISIONS
Creator: Duffty, Daniel
Date: 2015, 2015-05
Description: Our understanding of the fundamental interactions of particles has come far in the last century, and is still pushing forward. As we build...
Show moreOur understanding of the fundamental interactions of particles has come far in the last century, and is still pushing forward. As we build ever more powerful machines to probe higher and higher energies, we will need to develop new tools to not only understand the new physics objects we are trying to detect, but even to understand the environment that we are searching in. We examine methods of identifying both boosted objects and low energy jets which will be shrouded in a sea of noise from other pasts of the detector. We display the power of boosted-b tagging in a simulated W' search. We also examine the effetc of pile up on low energy jet reconstructions. For this purpose we develop a new priority-based jet algorithm, "p-jets", to cluster the energy that belongs together, but ignore the rest.
Ph.D in Physics, May 2015
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Title: UNDERSTANDING UNCERTAINTIES IN RESOLVED PHOTON STRUCTURE
Creator: Zhan, Hengrui
Date: 2017, 2017-07
Description: The construction of a photon collider has been urged, in order to study the properties of the Higgs boson and electroweak symmetry breaking....
Show moreThe construction of a photon collider has been urged, in order to study the properties of the Higgs boson and electroweak symmetry breaking. It would also provide unique possibilities for measurement of fusion to probe the hadronic structure of the photon. One scheme of design for the photon collider is a linear collider. A study shows that resolved photons contribute about 15% of the cross section to Higgs production with a mass of 120 GeV, but estimates of the resolved photon structure have so far varied greatly. Therefore, resolved photon structure is important to measure. This thesis focuses on the determination of the uncertainties of the cross section of bb production for better understanding of resolved photon structure. The principles of a photon collider are reviewed. In this thesis, the simulation tools for the simulation of the cross section of ! bb collision are developed. After that, the method for determination of the uncertainties of cross section is described. A new set of PDFs to explore these uncertainties is produced. The result of the simulation of the cross section and the calculation for the uncertainties of the cross section is presented and discussed in detailed.
M.S. in Physics, July 2017
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Title: INVESTIGATION OF NIOBIUM SURFACE STRUCTURE AND COMPOSITION FOR IMPROVEMENT OF SUPERCONDUCTING RADIO-FREQUENCY CAVITIES
Creator: Trenikhina, Yulia
Date: 2014, 2014-12
Description: Nano-scale investigation of intrinsic properties of niobium near-surface is a key to control performance of niobium superconducting radio...
Show moreNano-scale investigation of intrinsic properties of niobium near-surface is a key to control performance of niobium superconducting radio-frequency cavities. Mechanisms responsible for the performance limitations and their empirical remedies needs to be justified in order to reproducibly control fabrication of SRF cavities with desired characteristics. The high field Q-slope and mechanism behind its cure (120◦C mild vacuum bake) were investigated by comparison of the samples cut out of the cavities with high and low dissipation regions. Material evolution during mild field Q-slope nitrogen treatment was characterized using the coupon samples as well as samples cut out of nitrogen treated cavity. Evaluation of niobium near-surface state after some typical and novel cavity treatments was accomplished. Various TEM techniques, SEM, XPS, AES, XRD were used for the structural and chemical characterization of niobium near-surface. Combination of thermometry and structural temperature-dependent comparison of the cavity cutouts with different dissipation characteristics revealed precipitation of niobium hydrides to be the reason for medium and high field Q-slopes. Step-by-step effect of the nitrogen treatment processing on niobium surface was studied by analytical and structural characterization of the cavity cutout and niobium samples, which were subject to the treatment. Low concentration nitrogen doping is proposed to explain the benefit of nitrogen treatment. Chemical characterization of niobium samples before and after various surface processing (Electropolishing (EP), 800◦C bake, hydrofluoric acid (HF) rinsing) showed the differences that can help to reveal the microscopic effects behind these treatments as well as possible sources of surface contamination.
Ph.D. in Physics, December 2014
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Title: IRON INCORPORATION INTO FERROELECTRIC LEAD TITANATE
Creator: Ganegoda, Hasitha
Date: 2012-11-27, 2012-12
Description: Incorporation of iron into ferroelectric lead titanate with ABO3 perovskite structure is widely utilized to fabricate materials with...
Show moreIncorporation of iron into ferroelectric lead titanate with ABO3 perovskite structure is widely utilized to fabricate materials with ferroelectric and ferromagnetic order. These solid solutions exhibit room temperature ferromagnetic properties at iron concentration as low as 1 mole%. Iron (Fe3+) is highly compatible with titanium (Ti4+) in ionic radii and obviously incompatible in the valence state. Magnetoelectric coupling has been observed in 50 mole% Fe substituted lead titanate. The molecular mixing of precursor materials in wet chemical synthesis such as sol-gel has advantage over conventional solid state sintering in achieving higher solubility of the substituent. A series of Pb(FexTi1−x)O3− solid solution in the composition range x = 0 to 1 has been synthesized using sol-get route, followed by a moderate temperature (700 C) calcination. The structure and properties of samples were characterized using x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), dielectric spectroscopy, Raman spectroscopy, and magnetic measurements. SEM results indicated a gradual change in sample morphology, changing from individual particles to nano-aggregates with Fe concentration. EDX confirmed uniform distribution of dopants when Fe concentration x 0.3 and Fe concentration close to nominal composition with possibility of lead loss. XRD results indicated a rapid reduction of tetragonal distortion upon Fe substitution, Fe solubility limit of 10 mole%, and PbFe12O19 impurity phase formation at compositions x 0.4. XAS clearly indicated that Ti prefers a 6 coordinated distorted oxygen octahedra and Fe is surrounded by 5 oxygens situated at a similar distance. Other measurements suggested that ferroelectric and ferromagnetic ordering may arise in Ti-rich and Fe-rich phases, respectively. None of the samples below x = 0.2 was found to be ferromagnetic at room temperature.
PH.D in Physics, December 2012
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Title: MEASUREMENT OF 013 IN THE DOUBLE CHOOZ EXPERIMENT
Creator: Yang, Guang
Date: 2016, 2016-12
Description: Neutrino oscillation has been established for over a decade. The mixing angle 013 is one of the parameters that is most difficult to measure...
Show moreNeutrino oscillation has been established for over a decade. The mixing angle 013 is one of the parameters that is most difficult to measure due to its small value. Currently, reactor antineutrino experiments provide the best knowledge of 013, using the electron antineutrino disappearance phenomenon. The most compelling advantage is the high intensity of the reactor antineutrino rate. The Double Chooz experiment, located on the border of France and Belgium, is such an experiment, which aims to have one of the most precise 013 measurements in the world. Dou- ble Chooz has a single-detector phase and a double-detector phase. For the single- detector phase, the limit of the 013 sensitivity comes mostly from the reactor flux. However, the uncertainty on the reactor flux is highly suppressed in the double- detector phase. Oscillation analyses for the two phases have different strategies but need similar inputs, including background estimation, detection systematics evalua- tion, energy reconstruction and so on. The Double Chooz detectors are filled with gadolinium (Gd) doped liquid scintillator and use the inverse beta decay (IBD) sig- nal so that for each phase, there are two independent 013 measurements based on different neutron capturer (Gd or hydrogen). Multiple oscillation analyses are per- formed to provide the best 013 results. In addition to the 013 measurement, Double Chooz is also an excellent playground" to do diverse physics research. For example, a 252Cf calibration source study has been done to understand the spontaneous decay of this radioactive source. Further, Double Chooz also has the ability to do a sterile neutrino search in a certain mass region. Moreover, some new physics ideas can be tested in Double Chooz. In this thesis, the detailed methods to provide precise 013 measurement will be described and the other physics topics will be introduced.
Ph.D. in Pyhsics, December 2016
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Title: STUDIES IN NONEQUILIBRIUM STATISTICAL MECHANICS
Creator: Wang, Huichao
Date: 2013-05-08, 2013-05
Description: This thesis gives a brief outline of how the microscopic representation enters into a good description of the elasticity of a fluid. We first...
Show moreThis thesis gives a brief outline of how the microscopic representation enters into a good description of the elasticity of a fluid. We first introduce the hydrodynamics by three continuity equations. Due to its macroscopic background, we point out its limitation that it does not fit well with the elastic behavior of the fluid. Therefore we introduce the microscopic description of the system. In order to connect the elasticity which is obviously involved in the non-equilibrium state of a fluid, we discuss how non-equilibrium mechanics could be related to equilibrium mechanics by the assumption that the system is not far away from equilibrium. Under this assumption, an analysis of equilibrium mechanics is necessary, and combining with the microscopic representation, we derive the generalized Langevin equation as an equation of motion of the momentum current, which is endowed with the elastic property, consistent with observations of the fluid.
M.S. in in Physics, May 2013
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Title: A COMPRHENSIVE MECHANISTIC STUDY OF PEPTIDOMIMETICS ON MODEL MEMBRANE SYSTEMS
Creator: Bianchi, Christopher P.
Date: 2014, 2014-12
Description: Peptidomimetics are a broad class of structural variant synthetic mimics of antimicrobial peptides (AMPs). AMPs are natural antibiotics found...
Show morePeptidomimetics are a broad class of structural variant synthetic mimics of antimicrobial peptides (AMPs). AMPs are natural antibiotics found in almost entirety throughout all living organisms. Although, AMPs were once thought of as promising therapeutics to combat infectious bacteria, key shortcomings such as low bioavailability, as well as high manufacturing costs have prevented them from reaching a clinical market. Peptidomimetics capitalize on the characteristics of AMPs thought to be responsible for their antibacterial activity, such as net cationic charge and amphiphilicity, while introducing key structural differences. The principal mode of antibacterial activity of AMPs is causing disruption to the bacteria cell membrane of both Gram-positive and Gram-negative bacteria types. The complexities of cell membranes with their various lipid molecule species and proteins makes it difficult to determine mechanistic details of AMPs. It is for this reason model membrane systems such as Langmuir monolayers and supported bilayers composed of the lipid species found in that of actual cell membrane are used. In the present work we have investigated the mechanism of action of different types of peptidomimetics such as N-substituted glycines (peptoids) and oligomers of acylated-lysines (OAKs) on model bacteria and cancer cell membrane systems using various experimental techniques, such as epifluorescence microscopy (EFM), atomic force microscopy (AFM), X-ray reflectivity, and grazing incidence X-ray diffraction (GIXD). From these studies structure function relationships can be obtained, which help aid in the design of new and more effective peptidomimetics. Through these investigations it was found that the substitution of hydrogen atoms for fluorine atoms in the phenyl side chains of cyclic peptoids increases antibacterial on both Gram-positive and Gram-negative model membrane systems, guanidino containing side chains compared to amino containing side chains in α-peptide-β-peptoid chimeras show greater activity on model membrane systems mimicking the cytoplasmic membrane of both Gram-positive and Gram negative bacteria. In addition, insights were gained on the anticancer mechanisms of the naturally occurring AMP magainin-2 and OAK C12K-7α8. The significance of the model membrane system being used cannot be overstated, when the overall arching goal is to bring these peptidomimetics to a clinical market. Thus, the biological relevance of the model membrane system is of great importance. It is this motivation that has lead our research group to develop a floating planar lipid bilayer that is bound to a lipid monolayer functionalized with polyethylene glycol, which to our knowledge has not been previously done. This system and the planar Langmuir monolayer that were used in this work are ideal systems for the use of high energy X-rays that are produced from synchrotron radiation facilities. From such measurements as X-ray reflectivity (XR) and grazing incidence X-ray diffraction (GIXD) molecular scale resolution of the peptidomimetic interactions with the model membrane systems can be achieved.
Ph.D. in Physics, December 2014
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Title: LIPID-LIPID AND LIPID-DRUG INTERACTIONS IN BIOLOGICAL MEMBRANES
Creator: Martynowycz, Michael W.
Date: 2016, 2016-07
Description: Interactions between lipids and drug molecules in biological membranes help govern proper biological function in organisms. The mechanisms...
Show moreInteractions between lipids and drug molecules in biological membranes help govern proper biological function in organisms. The mechanisms responsible for hydrophobic drug permeation remain elusive. Many small molecule drugs are hydrophobic. These drugs inhibit proteins in the cellular interior. The rise of antibiotic resistance in bacteria is thought to be caused by mutations in protein structure, changing drug kinetics to favor growth. However, small molecule drugs have been shown to have different mechanisms depending in the structure of the lipid membrane of the target cell. Biological membranes are investigated using Langmuir monolayers at the airliquid interface. These offer the highest level of control in the mimetic system and allow them to be investigated using complementary techniques. Langmuir isotherms and insertion assays are used to determine the area occupied by each lipid in the membrane and the change in area caused by the introduction of a drug molecule, respectively. Specular X-ray re ectivity is used to determine the electron density of the monolayer, and grazing incidence X-ray diffraction is used to determine the inplane order of the monolayer. These methods determine the affinity of the drug and the mechanism of action. Studies are presented on hydrophobic drugs with mammalian membrane mimics using warfarin along with modified analogues, called superwarfarins. Data shows that toxicity of these modified drugs are modulated by the membrane cholesterol content in cells; explaining several previously unexplained effects of the drugs. Membrane mimics of bacteria are investigated along with their interactions with a hydrophobic antibiotic, novobiocin. Data suggests that permeation of the drug is mediated by modifications to the membrane lipids, and completely ceases translocation under certain circumstances.
Ph.D. in Physics, July 2016
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Title: THE PATH TO HIGH Q-FACTORS IN SUPERCONDUCTING ACCELERATING CAVITIES: FLUX EXPULSION AND SURFACE RESISTANCE OPTIMIZATION
Creator: Martinello, Martina
Date: 2016, 2016-12
Description: Accelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators....
Show moreAccelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators. Superconducting accelerating cavities are made out of niobium and operate at the liquid helium temperature. Even if superconducting, these resonating structures have some RF driven surface resistance that causes power dissipation. In order to decrease as much as possible the power losses, the cavity quality factor must be increased by decreasing the surface resistance. In this dissertation, the RF surface resistance is analyzed for a large variety of cavities made with different state-of-the-art surface treatments, with the goal of finding the surface treatment capable to return the highest Q-factor values in a cryomodule-like environment. This study analyzes not only the superconducting properties described by the BCS surface resistance, which is the contribution that takes into account dissipation due to quasi-particle excitations, but also the increasing of the surface resistance due to trapped flux. When cavities are cooled down below their critical temperature inside a cryomodule, there is always some remnant magnetic field that may be trapped increasing the global RF surface resistance. This thesis also analyzes how the fraction of external magnetic field, which is actually trapped in the cavity during the cooldown, can be minimized. This study is performed on an elliptical single-cell horizontally cooled cavity, resembling the geometry of cavities cooled in accelerator cryomodules. The horizontal cooldown study reveals that, as in case of the vertical cooldown, when the cooling is performed fast, large thermal gradients are created along the cavity helping magnetic flux expulsion. However, for this geometry the complete magnetic flux expulsion from the cavity equator is more difficult to achieve. This becomes even more challenging in presence of orthogonal magnetic field, that is easily trapped on top of the cavity equator causing temperature rising. The physics behind the magnetic flux expulsion is also analyzed, showing that during a fast cooldown the magnetic field structures, called vortices, tend to move in the same direction of the thermal gradient, from the Meissner state region to the mixed state region, minimizing the Gibbs free energy. On the other hand, during a slow cool down, not only the vortices movement is limited by the absence of thermal gradients, but, also, at the end of the superconducting transition, the magnetic field concentrates along randomly distributed normal-conducting region from which it cannot be expelled anymore. The systematic study of the surface resistance components performed for the different surface treatments, reveals that the BCS surface resistance and the trapped flux surface resistance have opposite trends as a function of the surface impurity content, defined by the mean free path. At medium field value, the BCS surface resistance is minimized for nitrogen-doped cavities and significantly larger for standard niobium cavities. On the other hand, Nitrogen-doped cavities show larger dissipation due to trapped flux. This is consequence of the bell-shaped trend of the trapped flux sensitivity as a function of the mean free path. Such experimental findings allow also a better understanding of the RF dissipation due to trapped flux. The best compromise between all the surface resistance components, taking into account the possibility of trapping some external magnetic field, is given by light nitrogen-doping treatments. However, the beneficial effects of the nitrogen-doping is completely lost when large amount of magnetic field is trapped during the cooldown, underlying the importance of both cooldown and magnetic field shielding optimization in high quality factors cryomodules.
Ph.D. in Physics, December 2016
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Title: PHOTOCATHODE TUNABILITY: THE PHOTOEMISSIVE PROPERTIES OF ULTRA-THIN MULTILAYERED MgO/Ag/MgO FILMS SYNTHESIZED BY PULSED LASER DEPOSITION
Creator: Velazquez, Daniel Gomez
Date: 2015, 2015-05
Description: Much of the early development of photocathode materials was aimed at the growth of photoemissive thin films with low work function, and high...
Show moreMuch of the early development of photocathode materials was aimed at the growth of photoemissive thin films with low work function, and high quantum efficiency (QE). It has been shown, both theoretically and experimentally, that metal-insulator junctions can lead to the modification of the work function and QE for coverages of a few monolayers of metal oxides on metallic substrates. However, the production of electron beams suitable for new photoinjector technologies in many instances requires low emittance beams from the cathode itself. Often the cathode intrinsic emittance plays an important role in new e-gun designs. A demonstration of the ability to control photoemissive properties by engineering the band structure of a photocathode could provide a pathway to meet the demands of new photoinjector technologies. Nemeth et al. [Phys. Rev. Lett. 104, 046801 (2010)] used density functional theory (DFT) to model the properties of a multilayered structure of MgO/Ag(001)/MgO with 4 monolayers of Ag(001) flanked by n monolayers (ML) of MgO. Their model indicated that it is possible to reduce the emittance of a photoemitted electron beam when the thickness n of the MgO layers is 2 or 3 monolayers because the surface band structure exhibits a narrowing of the density of occupied states in momentum near the Γ-point neighboring the Fermi Level. The theoretical prediction concerning the emission properties of these multilayers structures was tested by fabricating them, and then characterizing their emission properties. Synthesis of multilayered MgO/Ag/MgO films was performed using a custom-built pulsed laser deposition (PLD) system. In-situ growth monitoring was carried out by Reflection High-Energy Electron Diffraction (RHEED). Ex-situ techniques such as Scanning Tunneling Microscopy (STM), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (EDS) and Photoelectron Spectroscopy (PES) were used to show the formation of the crystalline and chemical structure of the multilayered films. A Kelvin Probe/photocurrent-detector system, custom-built for this research, was used to measure the work function and QE of the samples. Angle Resolved Photoelectron Spectroscopy was used to measure the angular photoelectron yield. Simultaneous reduction of work function and increase of QE was observed for (001) oriented multilayers of various thicknesses with respect to that of a bare Ag/MgO(001) surface. Work function measurements of multilayers of various thicknesses in the (111) orientation also registered a monotonic reduction with respect to that of a bare Ag/Si(111) surface. Angular emission was compared for a MgO/Ag/MgO multilayer (thicknesses of 3 ML/4 ML/3 ML) sample and Ag/MgO(001). Emission analysis of the angle-resolved photoelectron spectra shows a net change in the angular emission with high kinetic energy electron density shifted toward surface-normal emission. Experimental results were consistent with theoretical predictions, which open the promising possibility of customizing emission properties by direct manipulation of the surface band structure of the emitter.
Ph.D. in Physics, May 2015
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Title: FINITE ELEMENT ANALYSIS OF HIGH HEAT LOAD DEFORMATION AND MECHANICAL BENDING CORRECTION OF A BEAMLINE MIRROR FOR THE APS UPGRADE
Creator: Goldring, Nicholas
Date: 2017, 2017-07
Description: The impending Advanced Photon Source Upgrade (APS-U) will introduce a hard x-ray source that is set to surpass the current APS in brightness...
Show moreThe impending Advanced Photon Source Upgrade (APS-U) will introduce a hard x-ray source that is set to surpass the current APS in brightness and coherence by two to three orders of magnitude. To achieve this, the storage ring light source will be equipped with a multi-bend achromat (MBA) lattice [1]. In order to fully exploit and preserve the integrity of new beams actualized by upgraded storage ring components, improved beamline optics must also be introduced. The design process of new optics for the APS-U and other fourth generation synchrotrons involves the challenge of accommodating unprecedented heat loads. This dissertation presents an ex-situ analysis of heat load deformation and the subsequent mechanical bending correction of a 400 mm long, grazing-incidence, H2O side-cooled, reflecting mirror subjected to x-ray beams produced by the APS-U undulator source. Bending correction is measured as the smallest rms slope error, σrms, that can be resolved over a given length of the heat deformed geometry due to mechanical bending. Values of σrms in the <0.1 µrad regime represent a given mirror length over which incident x-ray beams from modern sources can be reflected without significant loss of quality [2, 3]. This study assumes a perfectly flat mirror surface and does not account for finish errors or other contributions to σrms beyond the scope of thermal deformation and elastic bending. The methodology of this research includes finite element analysis (FEA) employed conjointly with an analytical solution for mechanical bending deflection by means of an end couple. Additionally, the study will focus on two beam power density profiles predicted by the APS-U which were created using the software SRCalc [4]. The profiles account for a 6 GeV electron beam with second moment widths of 0.058 and 0.011 mm in the x- and y- directions respectively; the electron beam is passed through a 4.8 m long, 28 mm period APS-U undulator which produces the x-ray beam incident at a 3 mrad grazing angle on the flat mirror surface for both cases. The first power density profile is the most extreme case created by the undulator at it’s closest gap with a critical energy of 3 keV (ky=2.459); the second profile is generated for the case in which the undulator is tuned to emit at 8 keV (ky=1.026). The 3 keV case is of particular interest as it represents one of the most intense peak heat loads predicted to be incident on first optics at the APS-U. The FEA results revealed that the deflection due to the 3 keV heat load yields a 10.9 µrad rms slope error over the full mirror length. The projected correction via the elastic bending of the substrate yields a 0.10 µrad σrms within the center longitudinal 300 mm. The FEA also predicts that the 8 keV heat load deflection can be corrected to a σrms of 0.11 µrad within the center 300 mm from 1.50 µrad over the entire length. Attempts to optimize the end couple to correct over the entire 400 mm mirror length were unable to resolve the heat load deflection rms slope error to within a < 0.1 µrad value for either case. However, if a larger corrected surface is required, a longer mirror can be implemented so as to absorb the heat load of a larger beam than necessary which can then be cut by an aperture to the desired size and energy range.
M.S. in Physics, July 2017
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Title: SMALL MODULAR NUCLEAR REACTORS: LEARNING AND PRODUCTION
Creator: Kotlyarevsky, Arnold
Date: 2013, 2013-07
Description: Small Modular Nuclear Reactors o er a new alternative to carbon based energy sources in the energy market of the near future. Understanding...
Show moreSmall Modular Nuclear Reactors o er a new alternative to carbon based energy sources in the energy market of the near future. Understanding the economic forces driving the industrial manufacturing process is crucial to determining the viability of SMRs. This study is a continuation of research that developed a parametric model and initial production cost estimates for a generic 100MWe SMR integrated reactor vessel. The primary goal of this study was to characterize the learning rates, lot sizes, and optimum production of SMR IRVs using the parametric model and the initial cost estimates. Three separate models were developed based on increasing levels of learning transfer: no learning transfer, partial learning transfer, and full learning transfer. Models with no learning transfer and full learning transfer bounded the values for the learning curve expected for IRV manufacture. A model with a partial transfer of learning yielded production cost estimates of $312.2 million. Production of an SMR IRV based on this model is expected to see a learning rate 95.5%. Using the information from the other two models, the expected learning rate for IRV production is expected to fall between 93.3% and 99.1% Simulations of lot sizes of 1 to 12 were conducted to determine the manufacturing lot size that optimizes the factory setting. An optimum con guration of 5 units per lot was determined to be the minimum. However, the lot size is recommended to be increased to 6 units to withstand the possibility of cancellation. In this con guration, the average unit cost is $262 million, with a learning rate of 98.1%. Another important result indicates that optimum manufacturing outcomes are not necessarily correlated with higher levels of learning. Production in larger lot sizes is bene cial, especially for components that are few in number, like the pressure vessel.
M.S. in Physics, July 2013
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Title: HYBRID METHODS FOR SIMULATION OF MUON IONIZATION COOLING CHANNELS
Creator: Kunz, Josiah D.
Date: 2017, 2017-05
Description: COSY Infinity is an arbitrary-order beam dynamics simulation and analysis code. It can determine high-order transfer maps of combinations of...
Show moreCOSY Infinity is an arbitrary-order beam dynamics simulation and analysis code. It can determine high-order transfer maps of combinations of particle optical elements of arbitrary field configurations. For precision modeling, design, and optimization of next-generation muon beam facilities, its features make it a very attractive code. New features are being developed for inclusion in COSY to follow the distribution of charged particles through matter. To study in detail some of the properties of muons passing through material, the transfer map approach alone is not sufficient. The interplay of beam optics and atomic processes must be studied by a hybrid transfer map–Monte Carlo approach in which transfer map methods describe the average behavior of the particles in the accelerator channel including energy loss, and Monte Carlo methods are used to provide small corrections to the predictions of the transfer map accounting for the stochastic nature of scattering and straggling of particles. The advantage of the new approach is that it is very efficient in that the vast majority of the dynamics is represented by fast application of the high-order transfer map of an entire element and accumulated stochastic effects as well as possible particle decay. The gains in speed shown in this work are expected to simplify the optimization of muon cooling channels which are usually very computationally demanding due to the need to repeatedly run large numbers of particles through large numbers of configurations. This work describes the development of the required algorithms and their application to the simulation of muon ionization cooling channels. The code is benchmarked against other codes, validated with experimental results, and predicts results for current muon ionization cooling efforts.
Ph.D. in Physics, May 2017
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Title: ACOUSTIC LOCALIZATION OF BREAKDOWN IN RADIO FREQUENCY ACCELERATING CAVITIES
Creator: Lane, Peter
Date: 2016, 2016-07
Description: Current designs for muon accelerators require high-gradient radio frequency (RF) cavities to be placed in solenoidal magnetic fields. These...
Show moreCurrent designs for muon accelerators require high-gradient radio frequency (RF) cavities to be placed in solenoidal magnetic fields. These fields help contain and efficiently reduce the phase space volume of source muons in order to create a usable muon beam for collider and neutrino experiments. In this context and in general, the use of RF cavities in strong magnetic fields has its challenges. It has been found that placing normal conducting RF cavities in strong magnetic fields reduces the threshold at which RF cavity breakdown occurs. To aid the effort to study RF cavity breakdown in magnetic fields, it would be helpful to have a diagnostic tool which can localize the source of breakdown sparks inside the cavity. These sparks generate thermal shocks to small regions of the inner cavity wall that can be detected and localized using microphones attached to the outer cavity surface. Details on RF cavity sound sources as well as the hardware, software, and algorithms used to localize the source of sound emitted from breakdown thermal shocks are presented. In addition, results from simulations and experiments on three RF cavities, namely the Aluminum Mock Cavity, the High-Pressure Cavity, and the Modular Cavity, are also given. These results demonstrate the validity and effectiveness of the described technique for acoustic localization of breakdown.
Ph.D. in Physics, July 2016
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Title: LATTICE DESIGN OF THE INTEGRABLE OPTICS TEST ACCELERATOR AND OPTICAL STOCHASTIC COOLING EXPERIMENT AT FERMILAB
Creator: Kafka, Gene
Date: 2015, 2015-05
Description: The Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab will serve as the backbone for a broad spectrum of Advanced Accelerator...
Show moreThe Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab will serve as the backbone for a broad spectrum of Advanced Accelerator R&D (AARD) experiments, and as such, must be designed with significant flexibility in mind, but without compromising cost efficiency. The nonlinear experiments at IOTA will include: achievement of a large nonlinear tune shift/spread without degradation of dynamic aperture; suppression of strong lattice resonances; study of stability of nonlinear systems to perturbations; and studies of di↵erent variants of nonlinear magnet design. The ring optics control has challenging requirements that reach or exceed the present state of the art. The development of a complete self-consistent design of the IOTA ring optics, meeting the demands of all planned AARD experiments, is presented. Of particular interest are the precise control for nonlinear integrable optics experiments and the transverse-to-longitudinal coupling and phase stability for the Optical Stochastic Cooling Experiment (OSC). Since the beam time-of-flight must be tightly controlled in the OSC section, studies of second order corrections in this section are presented.
Ph.D. in Physics, May 2015
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Title: Fabrication and Characterization of High Aspect Ratio Hard X-ray Zone Plates with Ultrananocrystalline Diamond Molds
Creator: Wojcik, Michael J.
Date: 2013, 2013-05
Description: Hard x-ray zone plate development has played an important role in improving x-ray microscopy through ner resolution and greater functional X...
Show moreHard x-ray zone plate development has played an important role in improving x-ray microscopy through ner resolution and greater functional X-ray energy. Similar to circular di raction gratings except with changing period as a function of radius, zone plates are di ractive focusing optics with resolution determined by the outer most zone width (OZW). Hard X-ray zone plates are mostly phase zone plates with a limited e ciency that peaks when the zone material causes a -phase shift on the x-ray, and the zone thickness required can be multiple microns dependent on x-ray energy. The combination of sub-100-nm resolution and peak e ciency for hard xrays requires very high aspect ratio zones. In this dissertation, two materials were used to fabricate high aspect ratio zone plates in a single layer mold and a two layer mold process. Ultrananocrystalline diamond (UNCD) is composed of 2-5 nm diamond grains bounded together with graphitic bonds. This form of diamond can be deposited onto substrates with thickness greater than a micron and with physical properties similar to bulk diamond. Hydrogen silsesquioxane (HSQ) is a spin on glass that is also a high contrast electron beam lithography resist. A thick layer of HSQ can be patterned into high aspect ratio structures and could be used as a pattern transfer mask for several etch recipes. Both of these materials were used to fabricate up to 25 aspect ratio zone plates and with OZW of 60 and 80 nm. Zone plates fabricated with UNCD were the rst high aspect ratio zone plates using a diamond like material and this technique was leveraged into a new fabrication method using two layers as an electroplating mold. Fabricated zone plates were characterized to measure the optical properties to compare with the fabrication properties. After characterization, several zone plate models based on fabricated zone plates were developed and simulated using a wave propagation technique to compare with the characterization data. The results xiii from fabrication, characterization, and simulation of zone plates with 25 aspect ratio will be presented as well as future possibilities for the techniques used.
PH.D in Physics, May 2013
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