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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: 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: 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: 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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Title: SIMULTANEOUS INJECTION OF STABLE AND RADIOACTIVE IONS INTO UPGRADED MULTI-USER ATLAS
Creator: Perry, Amichay
Date: 2015, 2015-12
Description: Argonne Tandem Linac Accelerator System (ATLAS) is a Department of Energy (DOE) national user research facility, located at Argonne National...
Show moreArgonne Tandem Linac Accelerator System (ATLAS) is a Department of Energy (DOE) national user research facility, located at Argonne National Laboratory (ANL). Presently, Radioactive Ion Beams (RIBs) produced in the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility are charge bred in an Electron Cyclotron Resonance (ECR) charge breeder prior to post acceleration in ATLAS. A new state of the art Electron Beam Ion Source charge breeder, the CARIBU-EBIS charge breeder, has been developed (not in the scope of the work presented here) at ANL to replace the existing ECR for charge breeding RIBs generated in CARIBU. The CARIBU-EBIS charge breeder is now in the final stages of offline commissioning at the Accelerator Development Test Facility (ADTF). A significant part of the commissioning effort has been devoted to testing the source by breeding singlycharged cesium ions injected from a surface ionization source. Characterization of the CARIBU-EBIS performance has been accomplished through a comparison between the measured properties of extracted beams and simulation results. Following its offline commissioning, CARIBU-EBIS will be relocated to its permanent location in ATLAS. An electrostatic transport line has been designed to transport RIBs from CARIBU and inject them into CARIBU-EBIS. In addition, modifications to the existing ATLAS Low Energy Beam Transport (LEBT) were also required in order to transport the charge bred RIBs from CARIBU-EBIS to ATLAS. A proposal for upgrading ATLAS to a multi-user facility has been explored as well. In this context, beam dynamics simulations show that further modifications to the ATLAS LEBT will enable the simultaneous injection and acceleration of RIBs and stablebeams in ATLAS. Furthermore, a novel technique proposed by Ostroumov et al. will allow for the acceleration of multiple charge states from CARIBU-EBIS, thereby increasing the intensity of available RIBs by up to 60%.
Ph.D. in Physics, December 2015
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Title: THE VERY ENERGETIC RADIATION IMAGING TELESCOPE ARRAY SYSTEM OBSERVATIONS OF THE STARBURST GALAXY M82
Creator: Ratliff, Gayle
Date: 2015, 2015-07
Description: This work describes the Very Energetic Radiation Imaging Telescope Array Systems (VERITAS) observations of the starburst galaxy M82 by...
Show moreThis work describes the Very Energetic Radiation Imaging Telescope Array Systems (VERITAS) observations of the starburst galaxy M82 by documenting the analysis of 231 quality-selected hours of observational data taken between 2008 and 2014. The prototypical starburst galaxy, M82’s high supernova (SN) rate and dense central accumulation of molecular gas make it a promising candidate for studying cosmic ray (CR) acceleration and propagation with the detection of di↵use very high energy (VHE; approximately 100 GeV-100 TeV) !-ray emission. This di↵use emission is predicted to result from proton-proton interactions within the galaxy’s core that produce VHE !-rays through neutral pion decay. This work confirms the results of the initial VERITAS publication covering 137 hours of M82 observations between January 2008 and April 2009, yielding a total of 103.5 excess !-ray-like events (0.007 !/min, 5.7 pre-trial statistical significance) from a deeper exposure of 231 hours of observation. The spectral properties found are in agreement with the original detection within errors ("=2.85 ± 0.39). These results are consistent with paradigms that describe the production of CRs via the conversion of mechanical energy generated in supernovae (SNe). These findings will improve current di↵use emission models by better constraining galaxy parameters and by providing insight into CR proton loss processes and timescales, with further understanding to be gained with the introduction of the Cherenkov Telescope Array (CTA). xiiThis work describes the Very Energetic Radiation Imaging Telescope Array Systems (VERITAS) observations of the starburst galaxy M82 by documenting the analysis of 231 quality-selected hours of observational data taken between 2008 and 2014. The prototypical starburst galaxy, M82’s high supernova (SN) rate and dense central accumulation of molecular gas make it a promising candidate for studying cosmic ray (CR) acceleration and propagation with the detection of di↵use very high energy (VHE; approximately 100 GeV-100 TeV) !-ray emission. This di↵use emission is predicted to result from proton-proton interactions within the galaxy’s core that produce VHE !-rays through neutral pion decay. This work confirms the results of the initial VERITAS publication covering 137 hours of M82 observations between January 2008 and April 2009, yielding a total of 103.5 excess !-ray-like events (0.007 !/min, 5.7 pre-trial statistical significance) from a deeper exposure of 231 hours of observation. The spectral properties found are in agreement with the original detection within errors ("=2.85 ± 0.39). These results are consistent with paradigms that describe the production of CRs via the conversion of mechanical energy generated in supernovae (SNe). These findings will improve current di↵use emission models by better constraining galaxy parameters and by providing insight into CR proton loss processes and timescales, with further understanding to be gained with the introduction of the Cherenkov Telescope Array (CTA). xiiThis work describes the Very Energetic Radiation Imaging Telescope Array Systems (VERITAS) observations of the starburst galaxy M82 by documenting the analysis of 231 quality-selected hours of observational data taken between 2008 and 2014. The prototypical starburst galaxy, M82’s high supernova (SN) rate and dense central accumulation of molecular gas make it a promising candidate for studying cosmic ray (CR) acceleration and propagation with the detection of di↵use very high energy (VHE; approximately 100 GeV-100 TeV) !-ray emission. This di↵use emission is predicted to result from proton-proton interactions within the galaxy’s core that produce VHE !-rays through neutral pion decay. This work confirms the results of the initial VERITAS publication covering 137 hours of M82 observations between January 2008 and April 2009, yielding a total of 103.5 excess !-ray-like events (0.007 !/min, 5.7 pre-trial statistical significance) from a deeper exposure of 231 hours of observation. The spectral properties found are in agreement with the original detection within errors ("=2.85 ± 0.39). These results are consistent with paradigms that describe the production of CRs via the conversion of mechanical energy generated in supernovae (SNe). These findings will improve current di↵use emission models by better constraining galaxy parameters and by providing insight into CR proton loss processes and timescales, with further understanding to be gained with the introduction of the Cherenkov Telescope Array (CTA). xiiThis work describes the Very Energetic Radiation Imaging Telescope Array Systems (VERITAS) observations of the starburst galaxy M82 by documenting the analysis of 231 quality-selected hours of observational data taken between 2008 and 2014. The prototypical starburst galaxy, M82’s high supernova (SN) rate and dense central accumulation of molecular gas make it a promising candidate for studying cosmic ray (CR) acceleration and propagation with the detection of di↵use very high energy (VHE; approximately 100 GeV-100 TeV) !-ray emission. This di↵use emission is predicted to result from proton-proton interactions within the galaxy’s core that produce VHE !-rays through neutral pion decay. This work confirms the results of the initial VERITAS publication covering 137 hours of M82 observations between January 2008 and April 2009, yielding a total of 103.5 excess !-ray-like events (0.007 !/min, 5.7 pre-trial statistical significance) from a deeper exposure of 231 hours of observation. The spectral properties found are in agreement with the original detection within errors ("=2.85 ± 0.39). These results are consistent with paradigms that describe the production of CRs via the conversion of mechanical energy generated in supernovae (SNe). These findings will improve current di↵use emission models by better constraining galaxy parameters and by providing insight into CR proton loss processes and timescales, with further understanding to be gained with the introduction of the Cherenkov Telescope Array (CTA). xiiThis work describes the Very Energetic Radiation Imaging Telescope Array Systems (VERITAS) observations of the starburst galaxy M82 by documenting the analysis of 231 quality-selected hours of observational data taken between 2008 and 2014. The prototypical starburst galaxy, M82’s high supernova (SN) rate and dense central accumulation of molecular gas make it a promising candidate for studying cosmic ray (CR) acceleration and propagation with the detection of di↵use very high energy (VHE; approximately 100 GeV-100 TeV) !-ray emission. This di↵use emission is predicted to result from proton-proton interactions within the galaxy’s core that produce VHE !-rays through neutral pion decay. This work confirms the results of the initial VERITAS publication covering 137 hours of M82 observations between January 2008 and April 2009, yielding a total of 103.5 excess !-ray-like events (0.007 !/min, 5.7 pre-trial statistical significance) from a deeper exposure of 231 hours of observation. The spectral properties found are in agreement with the original detection within errors ("=2.85 ± 0.39). These results are consistent with paradigms that describe the production of CRs via the conversion of mechanical energy generated in supernovae (SNe). These findings will improve current di↵use emission models by better constraining galaxy parameters and by providing insight into CR proton loss processes and timescales, with further understanding to be gained with the introduction of the Cherenkov Telescope Array (CTA).
Ph.D. in Physics, July 2015
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Title: IN SITU X-RAY ABSORPTION SPECTROSCOPY STUDY OF TIN ANODE NANOMATERIALS FOR LITHIUM-ION BATTERIES
Creator: Pelliccione, Christopher J.
Date: 2015, 2015-05
Description: Tin is an attractive alternative to replace traditional carbon based anodes in lithium-ion batteries (LIBs) due to the nearly three-fold...
Show moreTin is an attractive alternative to replace traditional carbon based anodes in lithium-ion batteries (LIBs) due to the nearly three-fold increase in theoretical capacity over carbon. However, metallic tin su↵ers from volumetric expansion of the crystal structure during initial lithium insertion that quickly degrades the material and reduces the performance of the battery. Various techniques have been previously investigated with the goal of suppressing this destructive expansion by incorporating oxygen or a lithium-inactive metal into the tin to provide structural support and mitigate volumetric expansion. These materials show increased capacity retention compared to metallic tin, but still su↵er from capacity fading. The nature of these structural degradations must be fully understood to permit engineering of materials that avoid these destructive tendencies and can be considered as viable options for LIBs. In situ X-ray absorption spectroscopy (XAS) measurements were acquired on Sn, SnO2, Sn3 O2(OH)2, Cu6Sn5 and Ni3Sn4 nanoparticle anodes for LIBs. Accompanying the electrochemical characterization conducted on each material, the local atomic structure was modeled as a function of potential during the first charge and also as a function of charged/discharged states for several cycles. The extended X-ray absorption fine structure (EXAFS) theoretical modeling included the first unambiguous observation of Sn-Li coordination numbers and atomic distances in tin-based anode materials. From correlating the electrochemical performance to the EXAFS analysis, the long-term capacity retention of tin-based anodes is dependent on the structural deformations that occur during the first charge. The conversion of oxygen to amorphous Li2O, and the network that it forms, has a dramatic e↵ect on the kinetics of the system and the stability of the local metallic tin structure.
Ph.D. in Physics, May 2015
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Title: DESIGN OF A COVARIANCE MATRIX FITTER TO MEASURE THE ELECTRON ANTINEUTRINO OSCILLATION PARAMETERS USING NEUTRON HYDROGEN CAPTURE AT THE DAYA BAY EXPERIMENT
Creator: De Arcos Rodr´iguez, Jos´e Fernando
Date: 2015, 2015-12
Description: The Daya Bay experiment provided the first precision measurement of the third mixing angle of the Pontecorvo-Maki-Nakagawa-Sakata matrix (✓13)...
Show moreThe Daya Bay experiment provided the first precision measurement of the third mixing angle of the Pontecorvo-Maki-Nakagawa-Sakata matrix (✓13) using six detectors to determine the relative rates of correlated signals generated from gadolinium neutron capture and positron-electron annihilation gammas in the inverse beta decay process. An additional correlated hydrogen neutron capture signal is produced in the Daya Bay detectors. Its analysis has the potential of producing an independent measurement of the electron antineutrino oscillation parameters. In this thesis a fitter has been designed to measure ✓13 and the squared mass di↵erence (#m2 ee) using the shape information of the hydrogen neutron capture signal generated in the Daya Bay experiment detectors. The main challenges of the hydrogen capture signal are the high accidental background rates in the lower energy region, and hydrogen’s neutron capture cross-section being much lower than gadolinium’s. In order to have a significant signal, we had to use more aggressive selection cuts than those applied in the gadolinium neutron capture analysis, and the fiducial volume was expanded by including the gadolinium-free gamma catcher region. Both background and detector systematic uncertainties studies have been repeated for the new hydrogen signal conditions. The results of these studies have been used to produce the corresponding covariance matrices that account for the uncertainties in a covariance matrix fitter. The fitter is customizable, i.e., energy binning, antineutrino detector configuration, data periods to be fitted, reactor periods, detector response matrices and predictions can be configured using a graphical user interface, providing versatility for further research. The fitter performance has been tested in the two dimensional parameter space S ⇥ D, where S = !sin2(2✓13) 2 [0, 0.002, 0.004, ...0.2]} and D = {#m2 ee 2 [0.0015, 0.00152, 0.00154...0.0035]}, using nominal and statistically fluctuated antineutrino spectrum predictions.
Ph.D. in Physics, December 2015
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