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Articles 1 - 30 of 40
Full-Text Articles in Physics
An Interactive Simulation And Visualization Tool For Conventional And Aberration-Corrected Transmission Electron Microscopy, Xingzhong Li
An Interactive Simulation And Visualization Tool For Conventional And Aberration-Corrected Transmission Electron Microscopy, Xingzhong Li
Nebraska Center for Materials and Nanoscience: Faculty Publications
Contrast transfer function (CTF) is a vital function in transmission electron microscopy (TEM). It expresses to what extent amplitudes converted from the phase changes of the diffracted waves contribute to the TEM image, including the effects of lens aberrations. Simulation is very helpful to understand the application of the function thoroughly. In this work, we develop the CTFscope as a component in the Landyne software suite, to calculate the CTF with temporal and spatial dumping envelopes for conventional TEM and to extend it to various aberrations (up to fifth order) for aberration-corrected (AC)- TEM. It also includes effects on the …
Interband Transitions And Critical Points Of Single-Crystal Thoria Compared With Urania, Christina Dugan, Lu Wang, Kai Zhang, James M. Mann, Martin M. Kimani, Wai-Ning Mei, Peter A. Dowben, James C. Petrosky
Interband Transitions And Critical Points Of Single-Crystal Thoria Compared With Urania, Christina Dugan, Lu Wang, Kai Zhang, James M. Mann, Martin M. Kimani, Wai-Ning Mei, Peter A. Dowben, James C. Petrosky
Faculty Publications
The interband transitions of UO2 are validated independently through cathode luminescence. A picture emerges consistent with density functional theory. While theory is generally consistent with experiment, it is evident from the comparison of UO2 and ThO2 that the choice of functional can significantly alter the bandgap and some details of the band structure, in particular at the conduction band minimum. Strictly ab initio predictions of the optical properties of the actinide compounds, based on density functional theory alone, continue to be somewhat elusive.
Remote Surface Optical Phonon Scattering In Ferroelectric Ba0.6Sr0.4Tio3 Gated Graphene, Hanying Chen, Tianlin Li, Yifei Hao, Anil Rajapitamahuni, Zhiyong Xiao, Stefan Schoeche, Mathias Schubert, Xia Hong
Remote Surface Optical Phonon Scattering In Ferroelectric Ba0.6Sr0.4Tio3 Gated Graphene, Hanying Chen, Tianlin Li, Yifei Hao, Anil Rajapitamahuni, Zhiyong Xiao, Stefan Schoeche, Mathias Schubert, Xia Hong
Xia Hong Publications
We report the effect of remote surface optical (RSO) phonon scattering on carrier mobility in monolayer graphene gated by ferroelectric oxide. We fabricate monolayer graphene transistors back-gated by epitaxial (001) Ba0.6Sr0.4TiO3 films, with field effect mobility up to 23,000 cm2 V−1 s−1 achieved. Switching ferroelectric polarization induces nonvolatile modulation of resistance and quantum Hall effect in graphene at low temperatures. Ellipsometry spectroscopy studies reveal four pairs of optical phonon modes in Ba0.6Sr0.4TiO3, from which we extract RSO phonon frequencies. The temperature dependence of resistivity in graphene can be well accounted for …
Ultra-High Carrier Mobilities In Ferroelectric Domain Wall Corbino Cones At Room Temperature, Conor J. Mccluskey, Matthew G. Colbear, James P.V. Mcconville, Shane J. Mccartan, Jesi R. Maguire, Michele Conroy, Kalani Moore, Alan Harvey, Felix Trier, Ursel Bangert, Alexei Gruverman, Manuel Bibes, Amit Kumar, Raymong G.P. Mcquaid, J. Marty Gregg
Ultra-High Carrier Mobilities In Ferroelectric Domain Wall Corbino Cones At Room Temperature, Conor J. Mccluskey, Matthew G. Colbear, James P.V. Mcconville, Shane J. Mccartan, Jesi R. Maguire, Michele Conroy, Kalani Moore, Alan Harvey, Felix Trier, Ursel Bangert, Alexei Gruverman, Manuel Bibes, Amit Kumar, Raymong G.P. Mcquaid, J. Marty Gregg
Alexei Gruverman Publications
Recently, electrically conducting heterointerfaces between dissimilar band-insulators (such as lanthanum aluminate and strontium titanate) have attracted considerable research interest. Charge transport has been thoroughly explored and fundamental aspects of conduction firmly established. Perhaps surprisingly, similar insights into conceptually much simpler conducting homointerfaces, such as the domain walls that separate regions of different orientations of electrical polarisation within the same ferroelectric band-insulator, are not nearly so well-developed. Addressing this disparity, we herein report magnetoresistance in approximately conical 180° charged domain walls, which occur in partially switched ferroelectric thin film single crystal lithium niobate. This system is ideal for such measurements: firstly, …
Statistical Characteristics Of High-Frequency Gravity Waves Observed By An Airglow Imager At Andes Lidar Observatory, Alan Z. Liu, Bing Cao
Statistical Characteristics Of High-Frequency Gravity Waves Observed By An Airglow Imager At Andes Lidar Observatory, Alan Z. Liu, Bing Cao
Publications
The long-term statistical characteristics of high-frequency quasi-monochromatic gravity waves are presented using multi-year airglow images observed at Andes Lidar Observatory (ALO, 30.3° S, 70.7° W) in northern Chile. The distribution of primary gravity wave parameters including horizontal wavelength, vertical wavelength, intrinsic wave speed, and intrinsic wave period are obtained and are in the ranges of 20–30 km, 15–25 km, 50–100 m s−1, and 5–10 min, respectively. The duration of persistent gravity wave events captured by the imager approximately follows an exponential distribution with an average duration of 7–9 min. The waves tend to propagate against the local background winds and …
Electron Traps In Ag-Doped Li2B4O7 Crystals: The Role Of Ag Interstitial Ions, Timothy D. Gustafson, Brant E. Kananen, Nancy C. Giles, Brian C. Holloway, Volodymyr T. Adamiv, Ihor M. Teslyuk, Yaroslav V. Burak, Larry E. Halliburton
Electron Traps In Ag-Doped Li2B4O7 Crystals: The Role Of Ag Interstitial Ions, Timothy D. Gustafson, Brant E. Kananen, Nancy C. Giles, Brian C. Holloway, Volodymyr T. Adamiv, Ihor M. Teslyuk, Yaroslav V. Burak, Larry E. Halliburton
Faculty Publications
Electron paramagnetic resonance (EPR) is used to establish models for electron traps in Ag-doped lithium tetraborate (Li2B4O7) crystals. When exposed at room temperature to ionizing radiation, electrons are trapped at interstitial Ag+ ions and holes are trapped at Ag+ ions on Li+ sites. The trapped electrons occupy a 5s1 orbital on the interstitial Ag ions (some of the unpaired spin density is also on neighboring ions). Three EPR spectra are assigned to electrons trapped at interstitial Ag ions. Their g values are near 1.99 and they have resolved hyperfine structure …
Kemar Hats Head Orientation Directivity, Samuel D. Bellows, Timothy W. Leishman
Kemar Hats Head Orientation Directivity, Samuel D. Bellows, Timothy W. Leishman
Directivity
This directivity data set for a KEMAR head head-and-torso simulator (HATS) includes head orientations in 14 directions in 5° steps starting from 0° to 40° and then in 10° steps from 40° to 90°. The full spherical measurements followed at an a = 0.97 m radius with the mouth aperture at the spherical center. The sampling density and distribution followed the AES 5° dual-equiangular sampling standard, omitting the south pole (θ = 180°). Thus, each spherical directivity assessment included 36 polar-angle θ samples and 72 azimuthal-angle ϕ samples. The presented data include 22 1/3-octave bands, ranging from 80 Hz …
Flexible Dye-Sensitized Solar Cells Assisted With Lead-Free Perovskite Halide, Judy Fan
Flexible Dye-Sensitized Solar Cells Assisted With Lead-Free Perovskite Halide, Judy Fan
Physics Faculty Research
Dye-sensitized solar cells (DSSCs) have shown promising alternative to Si-based counterparts due to low-cost, abundant raw materials, and non-vacuum processing. Here, we report a solution-based process to create flexible DSSCs on aluminum foils. Mesoporous TiO2 electrode was directly deposited on Al foil through spin casting. After post-thermal annealing, the resultant samples render optical smooth, crack-free, and large nanocrystalline thin films. The as-prepared double-layer porous TiO2 thin film was incorporated with a porphyrin dye followed by a perovskite halide salt Cs2SnI6, as the hole transport material, replacing liquid electrolyte. A transparent conducting plastic sheet was …
Development Of Advanced Machine Learning Models For Analysis Of Plutonium Surrogate Optical Emission Spectra, Ashwin P. Rao, Phillip R. Jenkins, John D. Auxier Ii, Michael B. Shattan, Anil Patnaik
Development Of Advanced Machine Learning Models For Analysis Of Plutonium Surrogate Optical Emission Spectra, Ashwin P. Rao, Phillip R. Jenkins, John D. Auxier Ii, Michael B. Shattan, Anil Patnaik
Faculty Publications
This work investigates and applies machine learning paradigms seldom seen in analytical spectroscopy for quantification of gallium in cerium matrices via processing of laser-plasma spectra. Ensemble regressions, support vector machine regressions, Gaussian kernel regressions, and artificial neural network techniques are trained and tested on cerium-gallium pellet spectra. A thorough hyperparameter optimization experiment is conducted initially to determine the best design features for each model. The optimized models are evaluated for sensitivity and precision using the limit of detection (LoD) and root mean-squared error of prediction (RMSEP) metrics, respectively. Gaussian kernel regression yields the superlative predictive model with an RMSEP of …
A Modulated Structure Derived From The Xa-Type Mn2Rusn Heusler Compound, Xingzhong Li, Wen-Yong Zhang, Ralph Skomski, David J. Sellmyer
A Modulated Structure Derived From The Xa-Type Mn2Rusn Heusler Compound, Xingzhong Li, Wen-Yong Zhang, Ralph Skomski, David J. Sellmyer
Nebraska Center for Materials and Nanoscience: Faculty Publications
A modulated structure derived from the inverse Heusler phase (the XA-type and the disordered variant L21B-type) has been observed in rapidly quenched Mn2RuSn ribbons. The powder X-ray diffraction pattern of the quenched ribbons can be indexed as an L21B-type structure. Electron diffraction patterns of the new structure mostly resemble those of the XA-type (and the disordered variant L21B-type) structure and additional reflections with denser spacing indicate a long periodicity. Orthogonal domains of the modulated structure were revealed by a selected-area electron diffraction pattern and the corresponding dark-field transmission electron microscopy images. The structure was …
Localization Effects And Anomalous Hall Conductivity In A Disordered 3d Ferromagnet, Paul M. Shand, Y. Moua, G. Baker, Shah R. Valloppilly, Pavel V. Lukashev, Parashu Kharel
Localization Effects And Anomalous Hall Conductivity In A Disordered 3d Ferromagnet, Paul M. Shand, Y. Moua, G. Baker, Shah R. Valloppilly, Pavel V. Lukashev, Parashu Kharel
Nebraska Center for Materials and Nanoscience: Faculty Publications
We have prepared the Heusler alloy CoFeV0.5Mn0.5Si in bulk form via arc melting. CoFeV0.5Mn0.5Si is ferromagnetic with a Curie temperature of 657 K. The longitudinal resistivity exhibits a minimum at 150 K, which is attributable to competition between quantum interference corrections at low temperatures and inelastic scattering at higher temperatures. The magnetoresistance (MR) is positive and nearly linear at low temperatures and becomes negative at temperatures close to room temperature. The positive MR in the quantum correction regime is evidence of the presence of the enhanced electron interaction as a contributor to …
A Monolithic 3d Printed Axisymmetric Co-Flow Single And Compound Emulsion Generator, Amirreza Ghaznavi, Yang Lin, Mark Douvidzon, Adam Szmelter, Alannah Rodrigues, Malik Blackman, David Eddington, Tal Carmon, Lev Deych, Lan Yang, Jie Xu
A Monolithic 3d Printed Axisymmetric Co-Flow Single And Compound Emulsion Generator, Amirreza Ghaznavi, Yang Lin, Mark Douvidzon, Adam Szmelter, Alannah Rodrigues, Malik Blackman, David Eddington, Tal Carmon, Lev Deych, Lan Yang, Jie Xu
Publications and Research
We report a microfluidic droplet generator which can produce single and compound droplets using a 3D axisymmetric co-flow structure. The design considered for the fabrication of the device integrated a user-friendly and cost-effective 3D printing process. To verify the performance of the device, single and compound emulsions of deionized water and mineral oil were generated and their features such as size, generation frequency, and emulsion structures were successfully characterized. In addition, the generation of bio emulsions such as alginate and collagen aqueous droplets in mineral oil was demonstrated in this study. Overall, the monolithic 3D printed axisymmetric droplet generator could …
Enhanced Study Of Complex Systems By Unveiling Hidden Symmetries With Dynamical Visibility, Nhat Vu Minh Nguyen
Enhanced Study Of Complex Systems By Unveiling Hidden Symmetries With Dynamical Visibility, Nhat Vu Minh Nguyen
2022 Symposium
One of the great challenges in complex and chaotic dynamics is to reveal its deterministic structures. These temporal dynamical structures are sometimes a consequence of hidden symmetries. Detecting and understanding them can allow the study of complex systems even without knowing the full underlying mathematical description of the system. Here we introduce a new technique, called Dynamical Visibility, that quantifies temporal correlations of the dynamics based upon some symmetry conditions. This visibility measures the departure of the dynamics from internal symmetries. We apply this technique to well-known chaotic systems, such as the logistic map and the circle map, as well …
Studying The Conditions For Magnetic Reconnection In Solar Flares With And Without Precursor Flares, Seth H. Garland, Daniel J. Emmons, Robert D. Loper
Studying The Conditions For Magnetic Reconnection In Solar Flares With And Without Precursor Flares, Seth H. Garland, Daniel J. Emmons, Robert D. Loper
Faculty Publications
Forecasting of solar flares remains a challenge due to the limited understanding of the triggering mechanisms associated with magnetic reconnection, the primary physical phenomenon connected to these events. Studies have indicated that changes to the photospheric magnetic fields associated with magnetic reconnection – particularly in relation to the field helicity – occur during solar flare events. This study utilized data from the Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) and SpaceWeather HMI Active Region Patches (SHARPs) to analyze full vector-field component data of the photospheric magnetic field during solar flare events within a near decade long HMI dataset. …
What Happens When Transition Metal Trichalcogenides Are Interfaced With Gold?, Archit Dhingra, Dmitri E. Nikonov, Alexey Lipatov, Alexander Sinitskii, Peter Dowben
What Happens When Transition Metal Trichalcogenides Are Interfaced With Gold?, Archit Dhingra, Dmitri E. Nikonov, Alexey Lipatov, Alexander Sinitskii, Peter Dowben
Peter Dowben Publications
Transition metal trichalcogenides (TMTs) are two-dimensional (2D) systems with quasi-one-dimensional (quasi-1D) chains. These 2D materials are less susceptible to undesirable edge defects, which enhances their promise for low-dimensional optical and electronic device applications. However, so far, the performance of 2D devices based on TMTs has been hampered by contact-related issues. Therefore, in this review, a diligent effort has been made to both elucidate and summarize the interfacial interactions between gold and various TMTs, namely, In4Se3, TiS3, ZrS3, HfS3, and HfSe3. X-ray photoemission spectroscopy data, supported by the results …
High Resolution Diagnostic Tools For Superconducting Radio Frequency Cavities, I. Parajuli, G. Ciovati, J. R. Delayen
High Resolution Diagnostic Tools For Superconducting Radio Frequency Cavities, I. Parajuli, G. Ciovati, J. R. Delayen
Physics Faculty Publications
Superconducting radio-frequency (SRF) cavities are one of the fundamental building blocks of modern particle accelerators. To achieve the highest quality factors (1010–1011), SRF cavities are operated at liquid helium temperatures. Magnetic flux trapped on the surface of SRF cavities during cool-down below the critical temperature is one of the leading sources of residual RF losses. Instruments capable of detecting the distribution of trapped flux on the cavity surface are in high demand in order to better understand its relation to the cavity material, surface treatments and environmental conditions. We have designed, developed, and commissioned two high-resolution …
Preliminary Results From Magnetic Field Scanning System For A Single-Cell Niobium Cavity, Ishwari Prasad Parajuli, Gianluigi Ciovati, Jean R. Delayen, Alex V. Gurevich
Preliminary Results From Magnetic Field Scanning System For A Single-Cell Niobium Cavity, Ishwari Prasad Parajuli, Gianluigi Ciovati, Jean R. Delayen, Alex V. Gurevich
Physics Faculty Publications
One of the building blocks of modern particle accelerators is superconducting radiofrequency (SRF) cavities. Niobium is the material of choice to build such cavities, which operate at liquid helium temperature (2 - 4 K) and have some of the highest quality factors found in Nature. There are several sources of residual losses, one of them is trapped magnetic flux, which limits the quality factor in SRF cavities. The flux trapping mechanism depends on different niobium surface preparations and cool-down conditions. Suitable diagnostic tools are not yet available to study the effects of such conditions on magnetic flux trapping. A magnetic …
Nonlinear Meissner Effect In Nb3Sn Coplanar Resonators, Junki Makita, C. Sundahl, Gianluigi Ciovati, C. B. Eom, Alex Gurevich
Nonlinear Meissner Effect In Nb3Sn Coplanar Resonators, Junki Makita, C. Sundahl, Gianluigi Ciovati, C. B. Eom, Alex Gurevich
Physics Faculty Publications
We investigated the nonlinear Meissner effect (NLME) in Nb3Sn thin-film coplanar resonators by measuring the resonance frequency as a function of a parallel magnetic field at different temperatures. We used low rf power probing in films thinner than the London penetration depth λ(B) to significantly increase the field onset of vortex penetration and measure the NLME under equilibrium conditions. Contrary to the conventional quadratic increase of λ(B) with B expected in s-wave superconductors, we observed a nearly linear increase of the penetration depth with B. We concluded that this behavior of λ(B) is due to weak linked grain …
Cooling Performance In A Dual Energy Storage Ring Cooler, B. Dhital, Y. S. Derbenev, D. Douglas, G. A. Krafft, H. Zhang, F. Lin, V. S. Morozov, Y. Zhang
Cooling Performance In A Dual Energy Storage Ring Cooler, B. Dhital, Y. S. Derbenev, D. Douglas, G. A. Krafft, H. Zhang, F. Lin, V. S. Morozov, Y. Zhang
Physics Faculty Publications
The longitudinal and transverse emittance growth in hadron beams due to intra-beam scattering (IBS) and other heating sources deteriorate the luminosity in a collider. Hence, a strong hadron beam cooling is required to reduce and preserve the emittance. The cooling of high energy hadron beam is challenging. We propose a dual energy storage ring-based electron cooler that uses an electron beam to extract heat away from hadron beam in the cooler ring while the electron beam is cooled by synchrotron radiation damping in the high energy damping ring. In this paper, we present a design of a dual energy storage …
Cebaf Injector Model For KL Beam Conditions, Sunil Pokharel, Geoffrey A. Krafft, A. S. Hofler, R. Kazimi, M. Bruker, J. Grames, S. Zhang
Cebaf Injector Model For KL Beam Conditions, Sunil Pokharel, Geoffrey A. Krafft, A. S. Hofler, R. Kazimi, M. Bruker, J. Grames, S. Zhang
Physics Faculty Publications
The Jefferson Lab KL experiment will run at the Continuous Electron Beam Accelerator Facility with a much lower bunch repetition rate (7.80 or 15.59 MHz) than nominally used (249.5 or 499 MHz). While the proposed average current of 2.5 - 5.0 µA is relatively low compared to the maximum CEBAF current of approximately 180 µA, the corresponding bunch charge is atypically high for CEBAF injector operation. In this work, we investigated the evolution and transmission of low-rep-rate, high-bunch-charge (0.32 to 0.64 pC) beams through the CEBAF injector. Using the commercial software General Particle Tracer, we have simulated and analyzed the …
Modeling A Nb3Sn Cryounit In Gpt In Uitf, Sunil Pokharel, Geoffey A. Krafft, A. S. Hofler
Modeling A Nb3Sn Cryounit In Gpt In Uitf, Sunil Pokharel, Geoffey A. Krafft, A. S. Hofler
Physics Faculty Publications
Nb₃Sn is a prospective material for future superconducting RF (SRF) accelerator cavities. The material can achieve higher quality factors, higher temperature operation and potentially higher accelerating gradients (E_{acc} 96 MV/m) compared to conventional niobium. In this work, we performed modeling of the Upgraded Injector Test Facility (UITF) at Jefferson Lab utilizing newly constructed Nb₃Sn cavities. We studied the effects of the buncher cavity and varied the gun voltages from 200-500 keV. We have calibrated and optimized the SRF cavity gradients and phases for the Nb₃Sn five-cell cavities energy gains with the framework of General Particle Tracer (GPT). Our calculations show …
Improving The Electrostatic Design Of The Jefferson Lab 300 Kv Dc Photogun, S.A.K. Wijethunga, M. A. Mamun, R. Suleiman, C. Hernandez-Garcia, B. Bullard, J. R. Delayen, J. Grames, G. A. Krafft, G. Palacios-Serrano, M. Poelker
Improving The Electrostatic Design Of The Jefferson Lab 300 Kv Dc Photogun, S.A.K. Wijethunga, M. A. Mamun, R. Suleiman, C. Hernandez-Garcia, B. Bullard, J. R. Delayen, J. Grames, G. A. Krafft, G. Palacios-Serrano, M. Poelker
Physics Faculty Publications
The 300 kV DC high voltage photogun at Jefferson Lab was redesigned to deliver electron beams with a much higher bunch charge and improved beam properties. The original design provided only a modest longitudinal electric field (Ez) at the photocathode, which limited the achievable extracted bunch charge. To reach the bunch charge goal of approximately few nC with 75 ps full-width at half-maximum Gaussian laser pulse width, the existing DC high voltage photogun electrodes and anode–cathode gap were modified to increase Ez at the photocathode. In addition, the anode aperture was spatially shifted with respect to the beamline longitudinal axis …
Magnetic Field Mapping Of 1.3 Ghz Superconducting Radio Frequency Niobium Cavities, Ishwari P. Parajuli, Gianluigi Ciovati, Jean R. Delayen, Alex V. Gurevich
Magnetic Field Mapping Of 1.3 Ghz Superconducting Radio Frequency Niobium Cavities, Ishwari P. Parajuli, Gianluigi Ciovati, Jean R. Delayen, Alex V. Gurevich
Physics Faculty Publications
Niobium is the material of choice to build superconducting radio frequency (SRF) cavities, which are fundamental building blocks of modern particle accelerators. These cavities require a cryogenic cool-down to ~2 - 4 K for optimum performance minimizing RF losses on the inner cavity surface. However, temperature-independent residual losses in SRF cavities cannot be prevented entirely. One of the significant contributor to residual losses is trapped magnetic flux. The flux trapping mechanism depends on different factors, such as surface preparations and cool-down conditions. We have developed a diagnostic magnetic field scanning system (MFSS) using Hall probes and anisotropic magneto-resistance sensors to …
Preliminary Results Of Magnetic And Temperature Map System For 3 Ghz Superconducting Radio Frequency Cavities, Ishwari Parajuli, Bashu Khanal, Gianluigi Ciovati, Jean Delayen, Alex Gurevich
Preliminary Results Of Magnetic And Temperature Map System For 3 Ghz Superconducting Radio Frequency Cavities, Ishwari Parajuli, Bashu Khanal, Gianluigi Ciovati, Jean Delayen, Alex Gurevich
Physics Faculty Publications
Superconducting radio frequency (SRF) cavities are fundamental building blocks of modern particle accelerators. When we cool these cavities at cryogenic temperature ~2 – 4 K, we can get optimum performance by minimizing RF losses on the inner cavity surface. However, temperature-independent residual losses in SRF cavities cannot be prevented entirely. One of the leading sources of residual losses in SRF cavities is trapped magnetic flux. The flux trapping mechanism depends on different surface preparations and cool-down conditions. We have designed, developed, and commissioned a combined magnetic (B) and temperature (T) mapping system using anisotropic magneto-resistance (AMR) sensors and carbon resistors …
Direct Current Magnetic Hall Probe Technique For Measurement Of Field Penetration In Thin Film Superconductors For Superconducting Radio Frequency Resonators, Iresha Harshani Senevirathne, Alex Gurevich, Jean Delayen
Direct Current Magnetic Hall Probe Technique For Measurement Of Field Penetration In Thin Film Superconductors For Superconducting Radio Frequency Resonators, Iresha Harshani Senevirathne, Alex Gurevich, Jean Delayen
Physics Faculty Publications
Superconducting Radio Frequency (SRF) cavities used in particle accelerators are typically formed from or coated with superconducting materials. Currently, high purity niobium is the material of choice for SRF cavities that have been optimized to operate near their theoretical field limits. This brings about the need for significant R & D efforts to develop next generation superconducting materials that could outperform Nb and keep up with the demands of new accelerator facilities. To achieve high quality factors and accelerating gradients, the cavity material should be able to remain in the superconducting Meissner state under a high RF magnetic field without …
Evaluation Of Single-Cell Cavities Made Of Forged Ingot Niobium At Jefferson Lab, P. Dhakal, Bashu D. Khanal, Gianluigi Ciovati, G. R. Myneni
Evaluation Of Single-Cell Cavities Made Of Forged Ingot Niobium At Jefferson Lab, P. Dhakal, Bashu D. Khanal, Gianluigi Ciovati, G. R. Myneni
Physics Faculty Publications
Currently, fine grain niobium (Nb) (grain size ∼ 50 µm) and large grain Nb (grain size of a few cm) are being used for the fabrication of superconducting radio frequency (SRF) cavities. Medium grain forged ingot with grain size of a few hundred µm may be beneficial for cost-effectiveness as well as providing better performance for future SRF-based accelerators. Forged ingot Nb with medium grain size is a novel production method to obtain Nb discs used for the fabrication of superconducting radio frequency cavities. We have fabricated two 1.5 GHz single cell cavities made from forged Nb ingot with a …
Magnetic Flux Expulsion In Superconducting Radio-Frequency Niobium Cavities Made From Cold Worked Niobium, Bashu D. Khanal, S. Balachandran, S. Chetri, P. J. Lee, P. Dhakal
Magnetic Flux Expulsion In Superconducting Radio-Frequency Niobium Cavities Made From Cold Worked Niobium, Bashu D. Khanal, S. Balachandran, S. Chetri, P. J. Lee, P. Dhakal
Physics Faculty Publications
Trapped residual magnetic field during the cooldown of superconducting radio frequency (SRF) cavities is one of the primary source of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 - 100 μm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during cooldown, hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and …
Lower Temperature Annealing Of Vapor Diffused Nb3Sn For Accelerator Cavities, Jayendrika K. Tiskumara, Jean R. Delayen, G. V. Eremeev, U. Pudasaini
Lower Temperature Annealing Of Vapor Diffused Nb3Sn For Accelerator Cavities, Jayendrika K. Tiskumara, Jean R. Delayen, G. V. Eremeev, U. Pudasaini
Physics Faculty Publications
Nb3Sn is a next-generation superconducting material for the accelerator cavities with higher critical temperature and superheating field, both twice compared to Nb. It promises superior performance and higher operating temperature than Nb, resulting in significant cost reduction. So far, the Sn vapor diffusion method is the most preferred and successful technique to coat niobium cavities with Nb3Sn. Although several post-coating techniques (chemical, electrochemical, mechanical) have been explored to improve the surface quality of the coated surface, an effective process has yet to be found. Since there are only a few studies on the post-coating heat treatment …
Field Shielding Of NBT��N Based Multilayer Structure For Accelerating Cavities, Iresha Harshani Senevirathne, Jean R. Delayen, Alex Gurevich, D. R. Beverstock, A.-M. Valente-Feliciano
Field Shielding Of NBT��N Based Multilayer Structure For Accelerating Cavities, Iresha Harshani Senevirathne, Jean R. Delayen, Alex Gurevich, D. R. Beverstock, A.-M. Valente-Feliciano
Physics Faculty Publications
Over the past few decades, bulk niobium (Nb) has been the material of choice for superconducting radio frequency (SRF) cavities used in particle accelerators to achieve higher accelerating gradients and lower RF losses. Multi-layer (SIS) structures consisting of alternating thin layers of superconductor(S) and insulator(I) deposited on a bulk Nb have been proposed to enhance the peak surface magnetic field and sustain a higher accelerating gradient. In this study, multilayers based NbTiN and AlN deposited on bulk Nb are used to test the proposed enhancement using the DC magnetic Hall probe technique. The technique detects a penetrating magnetic field through …
Improved Electrostatic Design Of The Jefferson Lab 300 Kv Dc Photogun And The Minimization Of Beam Deflection, M. A. Mamun, D. B. Bullard, J. R. Delayen, J. M. Grames, C. Hernandez-Garcia, Geoffrey A. Krafft, M. Poelker, R. Suleiman, S.A.K. Wijethunga
Improved Electrostatic Design Of The Jefferson Lab 300 Kv Dc Photogun And The Minimization Of Beam Deflection, M. A. Mamun, D. B. Bullard, J. R. Delayen, J. M. Grames, C. Hernandez-Garcia, Geoffrey A. Krafft, M. Poelker, R. Suleiman, S.A.K. Wijethunga
Physics Faculty Publications
An electron beam with high bunch charge and high repetition rate is required for electron cooling of the ion beam to achieve the high luminosity required for the proposed electron-ion colliders. An improved design of the 300 kV DC high voltage photogun at Jefferson Lab was incorporated toward overcoming the beam loss and space charge current limitation experienced in the original design. To reach the bunch charge goal of ~ few nC within 75 ps bunches, the existing DC high voltage photogun electrodes and anode-cathode gap were modified to increase the longitudinal electric field (Ez) at the photocathode. The anode-cathode …