Plasma and Beam Physics Commons^™

Higher Order Mode Damping In Superconducting Spoke Cavities, C. S. Hopper, J. R. Delayen

Physics Faculty Publications

Parasitic higher order modes (HOMs) can be severely detrimental to the performance of superconducting cavities. For this reason, the mode spectrum and beam coupling strength must be examined in detail to determine which modes must be damped. One advantage of the spoke cavity geometry is that couplers can be placed on the outer body of the cavity rather than in the beam line space. We present an overview of the HOM properties of spoke cavities and methods for suppressing the most harmful ones.

Cryogenic Testing Of High-Velocity Spoke Cavities, C. S. Hopper, Hyekyoung Park, J. R. Delayen

Physics Faculty Publications

Spoke-loaded cavities are being investigated for the high-velocity regime. The relative compactness at low-frequency makes them attractive for applications requiring, or benefiting from, 4 K operation. Additionally, the large velocity acceptance makes them good candidates for the acceleration of high-velocity protons and ions. Here we present the results of cryogenic testing of a 325 MHz, β0 = 0.82 single-spoke cavity and a 500 MHz, β0 = 1 double-spoke cavity.

Fabrication And Measurements Of 500 Mhz Superconducting Double Spoke Cavity, Hyekyoung Park, C. S. Hopper, J. R. Delayen

Physics Faculty Publications

The 500 MHz double spoke cavity has been designed for a high velocity application such as a compact electron accelerator at Center for Accelerator Science at Old Dominion University and is being built at Jefferson Lab. The geometry specific to the double spoke cavity requires a variety of tooling and fixtures. Also a number of joints are expected to make it difficult to maintain the geometric deviation from the design minimal. This paper will report the fabrication technique, resulting tolerance from the design, and comparison between the measurements and simulations.

Plasma Processing Of Large Curved Surfaces For Superconducting Rf Cavity Modification, J. Upadhyay, Do Im, S. Popovic, A. M. Valente-Feliciano, L. Phillips, L. Vušković

Physics Faculty Publications

Plasma-based surface modification of niobium is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. We have demonstrated surface layer removal in an asymmetric nonplanar geometry, using a simple cylindrical cavity. The etching rate is highly correlated with the shape of the inner electrode, radio-frequency (rf) circuit elements, gas pressure, rf power, chlorine concentration in the Cl₂/Ar gas mixtures, residence time of reactive species, and temperature of the cavity. Using variable radius cylindrical electrodes, large-surface ring-shaped samples, and dc bias in the external circuit, we have measured substantial average etching rates and outlined the possibility …

Progress On The Interaction Region Design And Detector Integration At Jlab's Meic, V. S. Morozov, P. Brindza, A. Camsonne, Ya S. Derbenev, R. Ent, D. Gaskell, F. Lin, P. Nadel-Turonski, M. Ungaro, Y. Zhang, C. E. Hyde, K. Park, M. Sullivan, Z. W. Zhao

Physics Faculty Publications

One of the unique features of JLab's Medium-energy Electron-Ion Collider (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. We present an interaction region design developed with close integration of the detection and beam dynamical aspects. The dynamical aspect of the design rests on a symmetry-based concept for compensation of non-linear effects. The optics and geometry have been optimized to accommodate the detection requirements and to ensure the interaction region's modularity for ease …

Multipacting Optimization Of A 750 Mhz Rf Dipole, A. Castilla, J. R. Delayen

Physics Faculty Publications

Crab crossing schemes have been proposed to re-instate luminosity degradation due to crossing angles at the interaction points in next generation colliders to avoid the use of sharp bending magnets and their resulting large synchrotron radiation generation, highly undesirable in the detector region. The rf dipole has been considered for a different set of applications in several machines, both rings and linear colliders. We present in this paper a study of the effects on the multipacting levels and location depending on geometrical variations on the design for a crabbing/deflecting application in a high current (3/0.5 A), high repetition (750 MHz) …

Precision Measurements Of G¹ Of The Proton And The Deuteron With 6 Gev Electrons, Y. Prok, K. P. Adhikari, D. Adikaram, M. J. Amaryan, G. E. Dodge, N. Guler, A. Klein, S. Koirala, S. E. Kuhn, Clas Collaboration

Physics Faculty Publications

The inclusive polarized structure functions of the proton and deuteron, g^p₁ and g^d₁ , were measured with high statistical precision using polarized 6 GeV electrons incident on a polarized ammonia target in Hall B at Jefferson Laboratory. Electrons scattered at laboratory angles between 18 and 45 degrees were detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual deep inelastic region kinematics, Q² > 1 GeV² and the final-state invariant mass W >2 GeV, the ratio of polarized to unpolarized structure functions g₁/F₁ is found to be nearly independent of Q …

Neutron Spin Struccture With Polarized Deuterons And Spectator Proton Tagging At Eic, W. Cosyn, V. Guzey, D. W. Higinbotham, C. Hyde, S. Kuhn, P. Nadel-Turonski, K. Park, M. Sargsian, M. Strikman, C. Weiss

Physics Faculty Publications

The neutron's deep-inelastic structure functions provide essential information for the flavor separation of the nucleon parton densities, the nucleon spin decomposition, and precision studies of QCD phenomena in the flavor-singlet and nonsinglet sectors. Traditional inclusive measurements on nuclear targets are limited by dilution from scattering on protons, Fermi motion and binding effects, final-state interactions, and nuclear shadowing at x ≪ 0.1. An Electron-Ion Collider (EIC) would enable next-generation measurements of neutron structure with polarized deuteron beams and detection of forward-moving spectator protons over a wide range of recoil momenta (0 < pR < several 100MeV in the nucleus rest frame). The free neutron structure functions could be obtained by extrapolating the measured recoil momentum distributions to the on-shell point. The method eliminates nuclear modifications and can be applied to polarized scattering, as well as to semi-inclusive and exclusive final states. We review the prospects for neutron structure measurements with spectator tagging at EIC, the status of R&D efforts, and the accelerator and detector requirements.

Characterization Of Microwave Discharge Plasmas For Surface Processing, Milka Nikolic

Physics Theses & Dissertations

We have developed several diagnostic techniques to characterize two types of microwave (MW) discharge plasmas: a supersonic flowing argon MW discharge maintained in a cylindrical quartz cavity at frequency ƒ = 2.45 GHz and a pulse repetitive MW discharge in air at ƒ = 9.5 GHz. Low temperature MW discharges have been proven to posses attractive properties for plasma cleaning and etching of niobium surfaces of superconductive radio frequency (SRF) cavities. Plasma based surface modification technologies offer a promising alternative for etching and cleaning of SRF cavities. These technologies are low cost, environmentally friendly and easily controllable, and present a …

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.

Special Issue On Plenary And Invited Papers From Icops 2012, Felipe Iza, Carl Ekdahl, Michael G. Kong

Electrical & Computer Engineering Faculty Publications

The 39th International Conference on Plasma Science (ICOPS) was held in Edinburgh, Scotland in July 2012. This was the third time that the conference was organized outside North America, the previous ones being in Karlsruhe (Germany) in 2008 and Jeju (S. Korea) in 2003. The technical programme combined seven technical areas of plasma science and technology covering a wide range of topics. The conference featured a wide range of advances in innovative plasma and beam science and applications, and served as a venue for an international community to meet and discuss their ideas and research results. More than 800 abstracts …

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.

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.

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.

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) …

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 …

Application Of Chebyshev Formalism To Identify Nonlinear Magnetic Field Components In Beam Transport System, Michael Spata

Physics Theses & Dissertations

An experiment was conducted at Jefferson Lab's Continuous Electron Beam Accelerator Facility to develop a beam-based technique for characterizing the extent of the nonlinearity of the magnetic fields of a beam transport system. Horizontally and vertically oriented pairs of air-core kicker magnets were simultaneously driven at two different frequencies to provide a time-dependent transverse modulation of the beam orbit relative to the unperturbed reference orbit. Fourier decomposition of the position data at eight different points along the beamline was then used to measure the amplitude of these frequencies. For a purely linear transport system one expects to find solely the …

Case Studies In Many-Body Physics, Ana Samolov

Physics Theses & Dissertations

The many-body problem refers to any physical problem made of more than two interacting particles. With increasing number of particles in a system, their coupling and entanglement becomes more complex, and there is no general analytic solution even for a three-body classical or quantum systems. However, some of the most fascinating phenomena in nature are products of collective effects. Therefore, significant efforts have been made in both experiment and theory to unravel some specific many-body problems. If we look at still unanswered physics questions we see that for most of these problems addressing the many-body interactions is a key issue. …

Beam Dynamics Studies For Transverse Electromagnetic Mode Type Rf Deflectors, Shahid Ahmed, Geoffrey A. Krafft, Kirsten Deitrick, Subashini U. De Silva, Jean R. Delayen, Mike Spata, Michael Tiefenback, Alicia Hofler, Kevin Beard

Physics Faculty Publications

We have performed three-dimensional simulations of beam dynamics for transverse electromagnetic mode (TEM) type rf deflectors: normal and superconducting. The compact size of these cavities as compared to the conventional TM₁₁₀ type structures is more attractive particularly at low frequency. Highly concentrated electromagnetic fields between the parallel bars provide strong electrical stability to the beam for any mechanical disturbance. An array of six 2-cell normal conducting cavities or a single cell superconducting structure is enough to produce the required vertical displacement at the target point. Both the normal and superconducting structures show very small emittance dilution due to the …

Evidence For The Onset Of Color Transparency In Ρ0 Electroproduction Off Nuclei, L. El Fassi, L. Zana, H. Hafidi, M. Holtrop, B. Mustapha, W. K. Brooks, H. Hakobyan, Z. Zheng, K. P. Adhikari, D. Adikaram, M. J. Amaryan, H. Baghdasaryan, S. Bültmann, G. E. Dodge, C. E. Hyde, A. Klein, S. E. Kuhn, M. Mayer, H. Seraydaryan, L. B. Weinstein

Physics Faculty Publications

We have measured the nuclear transparency of the incoherent diffractive A( e , e ′ ρ⁰ ) process in ¹²C and ⁵⁶Fe targets relative to ²H using a 5 GeV electron beam. The nuclear transparency, the ratio of the produced ρ⁰ ʼs on a nucleus relative to deuterium, which is sensitive to ρA interaction, was studied as function of the coherence length (lc), a lifetime of the hadronic fluctuation of the virtual photon, and the four-momentum transfer squared (Q²). While the transparency for both ¹²C and ⁵⁶Fe …

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.

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.

Characterizations Of Atmospheric Pressure Low Temperature Plasma Jets And Their Applications, Erdinc Karakas

Electrical & Computer Engineering Theses & Dissertations

Atmospheric pressure low temperature plasma jets (APLTPJs) driven by short pulses have recently received great attention because of their potential in biomedical and environmental applications. This potential is due to their user-friendly features, such as low temperature, low risk of arcing, operation at atmospheric pressure, easy handheld operation, and low concentration of ozone generation. Recent experimental observations indicate that an ionization wave exists and propagates along the plasma jet. The plasma jet created by this ionization wave is not a continuous medium but rather consists of a bullet-like-structure known as "Plasma Bullet". More interestingly, these plasma bullets actually have a …

Ignition Of A Large Volume Plasma With A Plasma Jet, M. Laroussi, M. A. Akman

Electrical & Computer Engineering Faculty Publications

Here we report on a method to generate a long plasma plume and to ignite a large volume plasma by means of the jet. The plasma plume is generated by our tube reactor and then introduced into a chamber where the pressure is controlled. We discovered there are three operating phases:Aphasewhere the plume length remains approximately constant, followed by a second phase where the jet increases in length as the pressure decreases. Then at pressures below 70 Torr a mode transition occurs where the plume length decreases and the plasma expands until the entire chamber is filled.

Localized Surface Plasmon Resonance Of Single Silver Nanoparticles Studied By Dark-Field Optical Microscopy And Spectroscopy, Wei Cao, Tao Huang, Xiao-Hong Nancy Xu, Hani E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Localized surface plasmon resonance (LSPR) of Ag nanoparticles (NPs) with different shapes and disk-shaped Ag NP pairs with varying interparticle distance is studied using dark-field optical microscopy and spectroscopy (DFOMS). Disk-, square-, and triangular-shaped Ag NPs were fabricated on indium tin oxide-coated glass substrates by electron beam lithography. The LSPR spectra collected from single Ag NPs within 5×5 arrays using DFOMS exhibited pronounced redshifts as the NP shape changed from disk to square and to triangular. The shape-dependent experimental LSPR spectra are in good agreement with simulations using the discrete dipole approximation model, although there are small deviations in the …

Special Issue On Plenary And Invited Papers From Icops 2010, Ravi P. Joshi, Xinpei Lu, Yukinori Sakiyama

Electrical & Computer Engineering Faculty Publications

HE 37th IEEE International Conference on Plasma Science (ICOPS) was held in Norfolk, VA, from June 20 to June 24, 2010. The technical program combined seven technical-related areas of plasma science and a range of diverse topics. A total of 562 abstracts from 37 countries were accepted, and the technical program included four plenary talks. There were 217 oral and 345 poster presentations. The plenary talks were given by Prof. L. Boufendi on Dusty Plasmas, Prof. E. Kunhardt on Non-Equilibrium Plasma Sources, Dr. K. S. Budil on High Energy Density Physics, and Dr. M. Thumm on the use of gyrotrons …

Experimental Investigation Of A Non-Thermal Atmospheric Pressure Plasma Jet, Asma Begum

Electrical & Computer Engineering Theses & Dissertations

The main objective of this dissertation is to understand the formation of the plasma jet from the plasma pencil, and the propagation of the plasma jet in the ambient atmosphere where the effect of the external electric field is almost zero. Before investigating the formation and propagation phenomenon of the plasma jet, common physical properties of plasma jets are determined by using the imaging technique and optical emission spectroscopy. The first goal of this dissertation is to establish the laminar helium gas flow channel through a plasma pencil.

The formation position, formation time, and the criterion of the plasma jet …

Destruction Of Α -Synuclein Based Amyloid Fibrils By A Low Temperature Plasma Jet, Erdinc Karakas, Agatha Munyanyi, Lesley Greene, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

Amyloid fibrils are ordered beta-sheet aggregates that are associated with a number of neurodegenerative diseases such as Alzheimer and Parkinson. At present, there is no cure for these progressive and debilitating diseases. Here we report initial studies that indicate that low temperature atmospheric pressure plasma can break amyloid fibrils into smaller units in vitro. The plasma was generated by the plasma pencil, a device capable of emitting a long, low temperature plasma plume/jet. This avenue of research may facilitate the development of a plasma-based medical treatment.

Finite Element Analysis Of Ring-Shaped Emission Profile In Plasma Bullet, Yukinori Sakiyama, David B. Graves, Julien Jarrige, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

Using a one-way coupled model of neutral gas flow and plasma dynamics we report a mechanism to explain the ring-shaped emission pattern that has been observed experimentally in plasma bullets at atmospheric pressure. We solve a fluid model with the local field approximation in one-dimensional cylindrical coordinates, corresponding to a cross-section of a plasma bullet. Pulselike uniform electric field is assumed to be applied perpendicular to the simulation domain. Time and spatially resolved spectroscopic measurements support the simulation results.

Experimental Studies On The Plasma Bullet Propagation And Its Inhibition, Erdinc Karakas, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

Plasma bullets generated by atmospheric pressure low temperature plasma jets have recently been an active research topic due to their unique properties and their enhanced plasma chemistry. In this paper, experimental insights into the plasma bullet lifetime and its velocity are reported. Data obtained from intensified charge-coupled device camera and time-resolved optical emission spectroscopy (OES) elucidated the existence of a weakly ionized channel between the plasma bullet and its source (such as the plasma pencil). Factors responsible for the inhibition of the propagation of the bullet, such as low helium mole fraction, the magnitude of the applied voltage, and the …