Engineering Physics Commons^™

Effect Of Vortex Hotspots On The Radio-Frequency Surface Resistance Of Superconductors, A. Gurevich, G. Ciovati

Physics Faculty Publications

We present detailed experimental and theoretical investigations of hotspots produced by trapped vortex bundles and their effect on the radio-frequency (rf) surface resistance Rs of superconductors at low temperatures. Our measurements of Rs, combined with the temperature mapping and laser scanning of a 2.36-mm-thick Nb plate incorporated into a 3.3-GHz Nb resonator cavity cooled by the superfluid He at 2 K, revealed spatial scales and temperature distributions of hotspots and showed that they can be moved or split by thermal gradients produced by the scanning laser beam. These results, along with the observed hysteretic field dependence of Rs which can …

Magnetic Bunch Compression For A Compact Compton Source, B.R.P. Gamage, T. Satogata

Physics Faculty Publications

A compact electron accelerator suitable for Compton source applications is in design at the Center for Accelerator Science at Old Dominion University and Jefferson Lab. Here we discuss two options for transverse magnetic bunch compression and final focus, each involving a 4-dipole chicane with M56 tunable over a range of 1.5-2.0m with independent tuning of final focus to interaction point \beta*=5mm. One design has no net bending, while the other has net bending of 90 degrees and is suitable for compact corner placement.

Mechanical Analysis Of The 400 Mhz Rf-Dipole Crabbing Cavity Prototype For Lhc High Luminosity Upgrade, S. U. De Silva, H. Park, J. R. Delayen, Z. Li

Physics Faculty Publications

The proposed LHC high luminosity upgrade requires two crabbing systems in increasing the peak luminosity, operating both vertically and horizontally at two interaction points of IP1 and IP5. The required system has tight dimensional constraints and needs to achieve higher operational gradients. A proof-of-principle 400 MHz crabbing cavity design has been successfully tested and has proven to be an ideal candidate for the crabbing system. The cylindrical proof-of-principle rf-dipole design has been adapted in to a square shaped design to further meet the dimensional requirements. The new rf-dipole design has been optimized in meeting the requirements in rf-properties, higher order …

Multipole Field Effects For The Superconducting Parallel-Bar/Rf-Dipole Deflecting/Crabbing Cavities, S. U. De Silva, J. R. Delayen

Physics Faculty Publications

The superconducting parallel-bar deflecting/crabbing cavity is currently being considered as one of the design options in rf separation for the Jefferson Lab 12 GeV upgrade and for the crabbing cavity for the proposed LHC luminosity upgrade. Knowledge of multipole field effects is important for accurate beam dynamics study of rf structures. The multipole components can be accurately determined numerically using the electromagnetic surface field data in the rf structure. This paper discusses the detailed analysis of those components for the fundamental deflecting/crabbing mode and higher order modes in the parallel-bar deflecting/crabbing cavity.

Study Of Cavity Imperfection Impact On Rf-Parameters And Multipole Components In A Superconducting Rf-Dipole Cavity, R. G. Olave, J. R. Delayen, S. U. De Silva, Z. Li

Physics Faculty Publications

The ODU/SLAC superconducting rf-dipole cavity is under consideration for the crab-crossing system in the upcoming LHC luminosity upgrade. While the proposed cavity complies well within the rf-parameters and multipolar component restrictions for the LHC system, cavity imperfections arising from cavity fabrication, welding and frequency tuning may have a significant effect in these parameters. We report on an initial study of the impact of deviation from the ideal shape on the cavity’s performance in terms of rf-parameters and multipolar components.

Comparison Of Electromagnetic, Thermal And Mechanical Calculations With Rf Test Results In Rf Dipole Deflecting/Crabbing Cavities, H. Park, S. U. Silva, J. R. Delayen

Physics Faculty Publications

The current requirements of higher gradients and strict dimensional constraints in the emerging applications have required the designing of compact deflecting and crabbing rf structures. The superconducting rf-dipole cavity is one of the first novel compact designs with attractive properties such as higher gradients, higher shunt impedance and widely separated higher order modes. The recent tests performed on proof-of-principle designs of the rf-dipole geometry at 4.2 K and 2.0 K in a vertical test assembly have proven the designs to achieve higher gradients with higher intrinsic quality factors and easily processed multipacting conditions. The design frequency sensitivity to pressure (df/dp) …

Tests Of An Rf Dipole Crabbing Cavity For An Electron-Ion Collider, A. Castilla, J. R. Delayen

Physics Faculty Publications

On the scheme of developing a medium energy electron-ion collider (MEIC) at Jefferson Lab, we have designed a compact superconducting rf dipole cavity at 750 MHz to crab both electron and ion bunches and increase luminosities at the interaction points (IP) of the machine. Following the design optimization and characterization of the electromagnetic properties such as peak surface fields and shunt impedance, along with field nonuniformities, multipole components content, higher order modes (HOM) and multipacting, a prototype cavity was built by Niowave Inc. The 750 MHz prototype crab cavity has been tested at 4 K and is ready for re-testing …

Geometry Effects On Multipole Components And Beam Optics In High-Velocity Multi-Spoke Cavities, C. S. Hopper, K. Deitrick, J. R. Delayen

Physics Faculty Publications

Velocity-of-light, multi-spoke cavities are being proposed to accelerate electrons in a compact light-source [1]. There are strict requirements on the beam quality which require that the linac have only small non-uniformities in the accelerating field. Beam dynamics simulations have uncovered varying levels of focusing and defocusing in the proposed cavities, which is dependent on the geometry of the spoke in the vicinity of the beam path. Here we present results for the influence different spoke geometries have on the multipole components of the accelerating field and how these components, in turn, impact the simulated beam properties.

Demonstration Of A Novel Technique To Measure Two-Photon Exchange Effects In Elastic E±P Scattering, M. Niroula, L. B. Weinstein, D. Adikaram, J. Lanchiet, K. P. Adhikari, M. J. Amaryan, R. P. Bennett, C. E. Hyde, S.E. Kuhn, H. Seraydaryan

Physics Faculty Publications

Background: The discrepancy between proton electromagnetic form factors extracted using unpolarized and polarized scattering data is believed to be a consequence of two-photon exchange (TPE) effects. However, the calculations of TPE corrections have significant model dependence, and there is limited direct experimental evidence for such corrections.

Purpose: The TPE contributions depend on the sign of the lepton charge in e±p scattering, but the luminosities of secondary positron beams limited past measurement at large scattering angles, where the TPE effects are believe to be most significant. We present the results of a new experimental technique for making direct e±p comparisons, which …

Interaction Region Design And Detector Integration At Jlab's Meic, F. Lin, P. Brindza, Y. S. Derbenev, V. S. Morozov, R. Ent, P. Nadel-Turonski, Y. Zhang, C. E. Hyde, M. Sullivan

Physics Faculty Publications

The Electron Ion Collider (EIC) will be a next-generation facility for the study of the strong interaction (QCD). JLab's MEIC is designed for high luminosities of up to 10³⁴ cm^-² s^-¹. This is achieved in part due to an aggressively small beta-star, which imposes stringent requirements on the collider rings' dynamical properties. Additionally, one of the unique features of MEIC is a full-acceptance detector with a dedicated, small-angle, high-resolution detection system, capable of covering a wide range of momenta (and charge-to-mass ratios) with respect to the original ion beam to enable access to new physics. The detector …

Dynamics Of Non-Thermal Plasma Jets Under Variable Pressure, Mehmet Arda Akman

Electrical & Computer Engineering Theses & Dissertations

Non-thermal plasma (NTP) jets driven by short DC pulses have attracted the attention of researchers within the past decade due to their promising bio-medical applications in the fields of wound healing, cancer treatment and sterilization. The ability to operate at atmospheric pressure, room temperature and simple device configuration has greatly contributed to their appeal and adoption in the plasma science community. However, the mechanisms that sustain the plasma generation and propagation in ambient air are currently a topic of debate. For instance, what appears as a continuous stream of a plasma plume extending outwards from a plasma device into the …

Electric-Field-Induced Interfacial Instabilities Of A Soft Elastic Membrane Confined Between Viscous Layers, Mohar Dey, Dipankar Bandyopadhyay, Ashutosh Sharma, Shizhi Qian, Sang Woo Joo

Mechanical & Aerospace Engineering Faculty Publications

We explore the electric-field-induced interfacial instabilities of a trilayer composed of a thin elastic film confined between two viscous layers. A linear stability analysis (LSA) is performed to uncover the growth rate and length scale of the different unstable modes. Application of a normal external electric field on such a configuration can deform the two coupled elastic-viscous interfaces either by an in-phase bending or an antiphase squeezing mode. The bending mode has a long-wave nature, and is present even at a vanishingly small destabilizing field. In contrast, the squeezing mode has finite wave-number characteristics and originates only beyond a threshold …

Development Of Superconducting 500 Mhz Multi-Spoke Cavity For Electron Linacs, Dmitry Gorelov, Charles H. Boulware, Terry Grimm, Jean R. Delayen, C. S. Hopper, R. G. Olgave, Subashini U. De Silva

Physics Faculty Publications

Multi-spoke cavities are well-known options for acceleration of heavy and light ions. A recently developed multi-spoke cavity for β=1 presents an attractive opportunity to use this cavity type for electron accelerators. One of the main attractive features of this cavity type is its compactness for relatively low frequency. A simplified design at 500 MHz allowed building of a multi-spoke cavity and cryomodule in a 2-year time frame with confidence and development of effective manufacturing techniques. It also constitutes an important step in proving the usefulness of this kind of cavity design for new applications in the electron machines. Niowave is …

Characteristics And Fabrication Of A 499 Mhz Superconducting Deflecting Cavity For The Jefferson Lab 12 Gev Upgrade, Hyekyoung Park, Subashini U. De Silva, Jean R. Delayen

Physics Faculty Publications

A 499 MHz parallel bar superconducting deflecting cavity has been designed and optimized [1,2] for a possible implementation at the Jefferson Lab. Previously the mechanical analysis [3], mainly stress, was performed. Since then pressure sensitivity was studied further and the cavity parts were fabricated. The prototype cavity is not completed due to the renovation at Jefferson Lab which resulted in the temporary shutdown of the electron beam welding facility. This paper will present the analysis results and facts encountered during fabrication. The unique geometry of the cavity and its required mechanical strength present interesting manufacturing challenges.

Rf Modeling Using Parallel Codes Ace3p For The 400-Mhz Parallel-Bar/Ridged-Waveguide Compact Crab Cavity For The Lhc Hilumi Upgrade, Zenghai Li, Lixin Ge, Jean R. Delayen, Subashini U. De Silva

Physics Faculty Publications

Schemes utilizing crab cavities to achieve head-on beam-beam collisions were proposed for the LHC HiLumi upgrade. These crabbing schemes require that the crab cavities be compact in order to fit into the tight spacing available in the existing LHC beamlines at the location where the crab cavities will be installed. Under the support of US LARP program, Old Dominion University and SLAC have joint efforts to develop a 400-MHz compact superconducting crab cavity to meet the HiLumi upgrade requirements. In this paper, we will present the RF modeling and analysis of a parallel-bar/ridged-waveguide shaped 400-MHz compact cavity design that can …

High Power Test Of Rf Separator For 12 Gev Upgrade Of Cebaf At Jefferson Lab, S. Ahmed, M. Wissmann, J. Mammosser, M. Spata, C. Hovater, Geoffrey A. Krafft, Jean R. Delayen

Physics Faculty Publications

CEBAF at JLab is in the process of an energy upgrade from 6 GeV to 12 GeV. The existing setup of the RF separator cavities in the 5th pass will not be adequate enough to extract the highest energy (11 GeV) beam to any two existing halls (A, B or C) while simultaneously delivering to the new hall D in the case of the proposed 12 GeV upgrade of the machine. To restore this capability, several options including the extension of existing normal conducting (NC) and a potential 499 MHz TEM-type superconducting (SC) cavity design have been investigated using computer …

Engineering Of A Superconducting 400 Mhz Crabbing Cavity For The Lhc Hilumi Upgrade, Dmitry Gorelov, Terry Grimm, Subashini Uddika De Silva, Jean Roger Delayen

Physics Faculty Publications

The recently developed new simplified design for the 400 MHz LHC crabbing cavity presents attractive properties compared to conventional designs. The proposed approach can be equally compact in both transverse dimensions and allows horizontal as well as vertical deflection of the beam in the collider. The significant modification of the parallel-bar design with the bars merged to the side walls of the cavity gives improved properties, such as better mode separation and reduced surface fields [1]. A transverse deflecting voltage of 4.2 MV in a single cavity can be expected with the peak surface electric field lower then 45 MV/m …

Design Of Electron And Ion Crabbing Cavities For An Electron-Ion Collider, A. Castilla, Jean R. Delayen, Geoffrey A. Krafft

Physics Faculty Publications

Beyond the 12 GeV upgrade at the Jefferson Lab a Medium Energy Electron-Ion Collider (MEIC) is being considered. In order to achieve the desired high luminosities at the Interaction Points (IP), the use of crabbing cavities is under study. In this work, we will present up to date designs of superconducting cavities, considered for crabbing both ion and electron bunches. A discussion of properties such as peak surface fields and Higher Order Modes (HOMs) separation will be presented.

Meic Design Progress, S. Ahmed, Y. Zhang, Y.S. Derbenev, D. Douglas, R. Ent, A. Hutton, A. Kimber, G.A. Krafft, R. Li, F. Lin, V. S. Morozov, P. Nadel-Turonski, E. W. Nissen, R. Rimmer, F.C. Pilat, T. Satogata, C. Tennant, Balsa Terzić, H. Wang, S. Wang, B. C. Yunn, D. P. Barber, Y. Filatov, C. Hyde, A. M. Kondratenko, S. L. Manikonda, P. N. Ostroumov, M. K. Sullivan

Physics Faculty Publications

This paper will report the recent progress in the conceptual design of MEIC, a high luminosity medium energy polarized ring-ring electron-ion collider at Jefferson lab. The topics and achievements that will be covered are design of the ion large booster and the ERL-circulator-ring-based electron cooling facility, optimization of chromatic corrections and dynamic aperture studies, schemes and tracking simulations of lepton and ion polarization in the figure-8 collider ring, and the beam-beam and electron cooling simulations. A proposal of a test facility for the MEIC electron cooler will also be discussed.

Development Of Spoke Cavities For High Velocity Applications, C. S. Hopper, R. G. Olave, Jean R. Delayen

Physics Faculty Publications

In response to recent interest in alternatives to TM-type cavities for low-frequency, high-velocity applications we have initiated a program for the development of multispoke superconducting cavities. We have completed the electromagnetic design for two-spoke cavities operating at 325, 352, 500, and 700 MHz with a design velocity of β₀ = 0.82 or β₀ = 1. We present the results of the optimization, higher order mode (HOM) analysis, multipacting analysis, and an initial analysis of multipole effects of the fundamental accelerating mode.

Superconducting Spoke Cavities For Electron And High-Velocity Proton Linacs, J. R. Delayen

Physics Faculty Publications

Spoke resonantors are currently under development for many proton machines but these structures are also considered for high beta electron linacs as well. These structures compare well to traditional elliptical cavities.

Multipacting Analysis Of High-Velocity Superconducting Spoke Resonators, C. S. Hopper, J. R. Delayen

Physics Faculty Publications

Some of the advantages of superconducting spoke cavities are currently being investigated for the high-velocity regime. When determining a final, optimized geometry, one must consider the possible limiting effects multipacting could have on the cavity. We report on the results of analytical calculations and numerical simulations of multipacting electrons in superconducting spoke cavities and methods for reducing their impact.

Design And Development Of Superconducting Parallel-Bar Deflecting/Crabbing Cavities, Subashini De Silva, Jean R. Delayen

Physics Faculty Publications

The superconducting parallel-bar cavity is a deflecting/crabbing cavity with attractive properties that is being considered for a number of applications. We present the designs of a 499 MHz deflecting cavity developed for the Jefferson Lab 12 GeV Upgrade and a 400 MHz crabbing cavity for the LHC High Luminosity Upgrade. Prototypes of these two cavities are now under development and fabrication.

Integration Of Detector Into Interaction Region At Meic, V. S. Morozov, R. Ent, P. Nadel-Turonski, C. E. Hyde

Physics Faculty Publications

The Jefferson Lab's Medium-energy Electron Ion Collider (MEIC) is proposed as a next-generation facility for the study of strong interaction (QCD). Accessing the relevant physics requires a full-acceptance detector with a dedicated small-angle high-resolution detection system capable of covering a wide range of momenta (and charge-to-mass ratios) with respect to the original ion beam. We present a design of such a detection system integrated into the collider's interaction region, in which full acceptance is attained by letting small-angle collision products pass through the nearest elements of the machine final-focusing system for further detection. The proposed design is consistent with the …

Improving The Efficiency Of Organic Solar Cells By Varying The Material Concentration In The Photoactive Layer, Kevin Anthony Latimer

Electrical & Computer Engineering Theses & Dissertations

Polymer-fullerene bulk heterojunction solar cells have been a rapidly improving technology over the past decade. To further improve the relatively low energy conversion efficiencies of these solar cells, several modifications need to be made to the overall device structure. Emerging technologies include cells that are fabricated with interfacial layers to facilitate charge transport, and tandem structures are being introduced to harness the absorption spectrum of polymers with varying bandgap energies.

When new structures are implemented, each layer of the cell must be optimized in order for the entire device to function efficiently. The most volatile layer of these devices is …

Growth Of Alkali Antimonide Photosensitive Thin Films, George Annobil

Electrical & Computer Engineering Theses & Dissertations

The experiment performed in this research addresses the growth of an alkali antimonide photosensitive film. Research was conducted to understand and develop a growth technique for a unique vapor deposition system in a vacuum environment. Specifically, the grown film will be utilized as a photocathode, and hence quantum efficiency (QE) and photocathode lifetime measurements are conducted. The research presents the successful growth of the binary compound cesium antimonide with achieved quantum efficiency of ~0.07% at ~240V anode bias. This experimental result demonstrated that the deposition technique was reliable in producing a feasible cathode. It further allowed the verification of theoretical …

Analysis Of Interband, Intraband, And Plasmon Polariton Transitions In Silver Nanoparticle Films Via In Situ Real-Time Spectroscopic Ellipsometry, S. A. Little, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

The dielectric function of Ag nanoparticle films, deduced from an analysis of in situ real-time spectroscopic ellipsometry (RTSE) measurements, is found to evolve with time during deposition in close consistency with the film structure, deduced in the same RTSE analysis. In the nucleation regime, the intraband dielectric function component is absent and plasmon polariton behavior dominates. Only at nuclei contact, does the intraband amplitude appear, increasing above zero. Both intraband and plasmon amplitudes coexist during surface smoothening associated with coalescence. The intraband relaxation time increases rapidly after surface smoothening is complete, also in consistency with the thin film structural evolution.

Parametric Study On Instabilities In A Two-Layer Electromagnetohydrodynamic Channel Flow Confined Between Two Parallel Electrodes, P. Dinesh Sankar Reddy, Dipankar Bandyopadhyay, Sang Woo Joo, Ashutosh Sharma, Shizhi Qian

Mechanical & Aerospace Engineering Faculty Publications

Instabilities in a two-phase electromagnetohydrodynamic (EMHD) flow between a pair of parallel electrodes are explored. A linear stability analysis has been performed based on a coupled Orr-Sommerfeld system generated from the conservation laws. The study shows the presence of a finite-wave-number EMHD mode of instability in addition to the two commonly observed instability modes in the pressure-driven two-layer flows, namely, the long-wave interfacial mode arising from the viscosity or density stratification and the finite-wave-number shear flow mode engendered by the Reynolds stresses. This extra EMHD mode originates from the additional stresses generated by the Lorenz force acting at the liquid …

Design Of Superconducting Spoke Cavities For High-Velocity Applications, Jean R. Delayen, Subashini De Silva, C. S. Hopper

Physics Faculty Publications

Superconducting single- and multi-spoke cavities have been designed to-date for particle velocities from β₀ ~ 0.15 to β₀ ~ 0.65. Superconducting spoke cavities may also be of interest for higher-velocity, low-frequency applications, either for hadrons or electrons. We present the design of spoke cavities optimized for β₀ = 0.8 and β₀ = 1.

Crab Crossing Consideration For Meic, S. Ahmed, Y. Derbenev, Geoffrey A. Krafft, Y. Zhang, Subashini De Silva, Jean R. Delayen, A. Castilla

Physics Faculty Publications

Crab crossing of colliding electron and ion beams is essential for accommodating the high bunch repetition frequency in the conceptual design of MEIC – a high luminosity polarized electron-ion collider at Jefferson Lab. The scheme eliminates parasitic beam-beam interactions and avoids luminosity reduction by restoring head-on collisions at interaction points. In this paper, we report the possible crabbing schemes and requirements for both electron and proton beams.