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Full-Text Articles in Physics

Harmonically Resonant Cavity As A Bunch Length Monitor, B. Roberts, M. Pablo, E. Forman, J. Grames, F. Hannon, R.Kazimi W. Moore, M. M. Ali Feb 2017

Harmonically Resonant Cavity As A Bunch Length Monitor, B. Roberts, M. Pablo, E. Forman, J. Grames, F. Hannon, R.Kazimi W. Moore, M. M. Ali

Physics Faculty Publications

A compact, harmonically-resonant cavity with a fundamental resonant frequency of 1497 MHz was used to evaluate the temporal characteristics of electron bunches produced by a 130 kV dc high voltage spin-polarized photoelectron source at the Continuous Beam Accelerator Facility (CEBAF) photoinjector, delivered at 249.5 and 499 MHz repetition rates and ranging in width from 45 to 150 picoseconds (FWHM). The cavity’s antenna was attached directly to a sampling oscilloscope that detected the electron bunches as they passed through the cavity bore with a sensitivity of ~ mV/ μA. The oscilloscope wave-forms are a superposition of the harmonic modes excited ...


Optimization Of The Rf Cavity Heat Load And Trip Rates For Cebaf At 12 Gev, H. Zhang, Y. Roblin, A. Freyberger, G. Krafft, B. Terzić Jan 2017

Optimization Of The Rf Cavity Heat Load And Trip Rates For Cebaf At 12 Gev, H. Zhang, Y. Roblin, A. Freyberger, G. Krafft, B. Terzić

Physics Faculty Publications

The Continuous Electron Beam Accelerator Facility at JLab has 200 RF cavities in the north linac and the south linac respectively after the 12 GeV upgrade. The purpose of this work is to simultaneously optimize the heat load and the trip rate for the cavities and to reconstruct the pareto-optimal front in a timely manner when some of the cavities are turned down. By choosing an efficient optimizer and strategically creating the initial gradients, the pareto-optimal front for no more than 15 cavities down can be re-established within 20 seconds.


Influence Of Orbital Symmetry On Diffraction Imaging With Rescattering Electron Wave Packets, Michael G. Pullen, Benjamin Wolter, Anh-Thu Le, Matthias Baudisch, Michele Sclafani, Hugo Pires, Claus Dieter Schroeter, Joachim Ullrich, Robert Moshammer, Thomas Pfeifer, C. D. Lin, Jens Biegert Jun 2016

Influence Of Orbital Symmetry On Diffraction Imaging With Rescattering Electron Wave Packets, Michael G. Pullen, Benjamin Wolter, Anh-Thu Le, Matthias Baudisch, Michele Sclafani, Hugo Pires, Claus Dieter Schroeter, Joachim Ullrich, Robert Moshammer, Thomas Pfeifer, C. D. Lin, Jens Biegert

Physics Faculty Research & Creative Works

The ability to directly follow and time-resolve the rearrangement of the nuclei within molecules is a frontier of science that requires atomic spatial and few-femtosecond temporal resolutions. While laser-induced electron diffraction can meet these requirements, it was recently concluded that molecules with particular orbital symmetries (such as πg) cannot be imaged using purely backscattering electron wave packets without molecular alignment. Here, we demonstrate, in direct contradiction to these findings, that the orientation and shape of molecular orbitals presents no impediment for retrieving molecular structure with adequate sampling of the momentum transfer space. We overcome previous issues by showcasing retrieval ...


Development Of The Electron Cooling Simulation Program For Jleic, H. Zhang, J. Chen, R. Li, Y. Zhang, H. Huang, L. Luo Jan 2016

Development Of The Electron Cooling Simulation Program For Jleic, H. Zhang, J. Chen, R. Li, Y. Zhang, H. Huang, L. Luo

Mathematics & Statistics Faculty Publications

In the JLab Electron Ion Collider (JLEIC) project the traditional electron cooling technique is used to reduce the ion beam emittance at the booster ring, and to compensate the intrabeam scattering effect and maintain the ion beam emittance during collision at the collider ring. A new electron cooling process simulation program has been developed to fulfill the requirements of the JLEIC electron cooler design. The new program allows the users to calculate the electron cooling rate and simulate the cooling process with either DC or bunched electron beam to cool either coasting or bunched ion beam. It has been benchmarked ...


High-Fidelity Simulations Of Long-Term Beam-Beam Dynamics On Gpus, B. Terzić, K. Arumugam, M. Aturban, C. Cotnoir, A. Godunov, D. Ranjan, M. Stefani, M. Zubair, F. Lin, V. Morozov, Y. Roblin, H. Zhang Jan 2016

High-Fidelity Simulations Of Long-Term Beam-Beam Dynamics On Gpus, B. Terzić, K. Arumugam, M. Aturban, C. Cotnoir, A. Godunov, D. Ranjan, M. Stefani, M. Zubair, F. Lin, V. Morozov, Y. Roblin, H. Zhang

Physics Faculty Publications

Future machines such as the Electron Ion Collider (MEIC), linac-ring machines (eRHIC) or LHeC are particularly sensitive to beam-beam effects. This is the limiting factor for long-term stability and high luminosity reach. The complexity of the non-linear dynamics makes it challenging to perform such simulations typically requiring millions of turns. Until recently, most of the methods have involved using linear approximations and/or tracking for a limited number of turns. We have developed a framework which exploits a massively parallel Graphical Processing Units (GPU) architecture to allow for tracking millions of turns in a sympletic way up to an arbitrary ...


Imaging An Aligned Polyatomic Molecule With Laser-Induced Electron Diffraction, Michael G. Pullen, Benjamin Wolter, Anh-Thu Le, Matthias Baudisch, Michael Hemmer, Arne Senftleben, Claus Dieter Schroeter, Joachim Ullrich, Robert Moshammer, C. D. Lin, Jens Biegert Jun 2015

Imaging An Aligned Polyatomic Molecule With Laser-Induced Electron Diffraction, Michael G. Pullen, Benjamin Wolter, Anh-Thu Le, Matthias Baudisch, Michael Hemmer, Arne Senftleben, Claus Dieter Schroeter, Joachim Ullrich, Robert Moshammer, C. D. Lin, Jens Biegert

Physics Faculty Research & Creative Works

Laser-induced electron diffraction is an evolving tabletop method that aims to image ultrafast structural changes in gas-phase polyatomic molecules with sub-Ångström spatial and femtosecond temporal resolutions. Here we demonstrate the retrieval of multiple bond lengths from a polyatomic molecule by simultaneously measuring the C-C and C-H bond lengths in aligned acetylene. Our approach takes the method beyond the hitherto achieved imaging of simple diatomic molecules and is based on the combination of a 160kHz mid-infrared few-cycle laser source with full three-dimensional electron-ion coincidence detection. Our technique provides an accessible and robust route towards imaging ultrafast processes in complex gas-phase molecules ...


Surface Microstructure Evolution Of Metallic Specimens Using The Large Chamber Scanning Electron Microscope, Grace Egbujor May 2015

Surface Microstructure Evolution Of Metallic Specimens Using The Large Chamber Scanning Electron Microscope, Grace Egbujor

Masters Theses & Specialist Projects

An initial study into the use of the large chamber scanning electron microscope (LCSEM) to interrogate the surface microstructure evolution of metallic specimens has been carried out. The LC-SEM located at Western Kentucky University is the largest instrument of its type at any university in the world. As such, unique measurements can be performed due to the size of its chamber and extended view of its optic system. Strain was varied for each individual specimen, and imaged using Secondary Electrons within the gauge length as well as near the grip position. Results will show progression of surface microstructures and nickel ...


Peppo: Using A Polarized Electron Beam To Produce Polarized Positrons, A. Adeyemi, G.L Gueye, P.A. Adderly, M. L. Stutzman, M. M. Ali, H. Areti, J. F. Benesch, L. S. Cardman, J. Clark, S. Covert, S. Golge, C. Hyde Jan 2015

Peppo: Using A Polarized Electron Beam To Produce Polarized Positrons, A. Adeyemi, G.L Gueye, P.A. Adderly, M. L. Stutzman, M. M. Ali, H. Areti, J. F. Benesch, L. S. Cardman, J. Clark, S. Covert, S. Golge, C. Hyde

Physics Faculty Publications

An experiment demonstrating a new method for producing polarized positrons has been performed at the CEBAF accelerator at Jefferson Laboratory. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e+/e pairs originating from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a 1.0 mm tungsten pair-production target. This paper describes preliminary results of measurements using an 8.2 MeV/c electron beam with polarization 84% to generate positrons in the range of 3.1 to 6.2 MeV/c with polarization as high as ∼80%.


Effects Of Plasma Processing On Secondary Electron Yield Of Niobium Samples, M. Basovic, S. Popovic, M. Tomovic, L. Vuskovic, A. Samolov, F. Cuckov Jan 2015

Effects Of Plasma Processing On Secondary Electron Yield Of Niobium Samples, M. Basovic, S. Popovic, M. Tomovic, L. Vuskovic, A. Samolov, F. Cuckov

Physics Faculty Publications

Impurities deposited on the surface of Nb during both the forming and welding of accelerator cavities add to the imperfections of the sheet metal, which then affects the overall performance of the cavities. This leads to a drop in the Q factor and limits the maximum acceleration gradient achievable per unit length of the cavities. The performance can be improved either by adjusting the fabrication and preparation parameters, or by mitigating the effects of fabrication and preparation techniques used. We have developed the experimental setup to determine Secondary Electron Yield (SEY) from the surface of Nb samples. Our aim is ...


High-Performance Simulations Of Coherent Synchrotron Radiation On Multicore Gpu And Cpu Platforms, B. Terzić, A. Godunov, K. Arumugam, D. Ranjan, M. Zubair Jan 2015

High-Performance Simulations Of Coherent Synchrotron Radiation On Multicore Gpu And Cpu Platforms, B. Terzić, A. Godunov, K. Arumugam, D. Ranjan, M. Zubair

Physics Faculty Publications

Coherent synchrotron radiation (CSR) is an effect of self-interaction of an electron bunch as it traverses a curved path. It can cause a significant emittance degradation and microbunching. We present a new high-performance 2D, particle-in-cell code which uses massively parallel multicore GPU/GPU platforms to alleviate computational bottlenecks. The code formulates the CSR problem from first principles by using the retarded scalar and vector potentials to compute the self-interaction fields. The speedup due to the parallel implementation on GPU/CPU platforms exceeds three orders of magnitude, thereby bringing a previously intractable problem within reach. The accuracy of the code is ...


Universality Of Returning Electron Wave Packet In High-Order Harmonic Generation With Midinfrared Laser Pulses, Anh-Thu Le, Hui Wei, Cheng Jin, Vu Ngoc Tuoc, Toru Morishita, C. D. Lin Jul 2014

Universality Of Returning Electron Wave Packet In High-Order Harmonic Generation With Midinfrared Laser Pulses, Anh-Thu Le, Hui Wei, Cheng Jin, Vu Ngoc Tuoc, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

We show that a returning electron wave packet in high-order harmonic generation (HHG) with midinfrared laser pulses converges to a universal limit for a laser wavelength above about 3µm. The results are consistent among the different methods: a numerical solution of the time-dependent Schrödinger equation, the strong-field approximation, and the quantum orbits theory. We further analyze how the contribution from different electron "trajectories" survives the macroscopic propagation in the medium. Our result thus provides a new framework for investigating the wavelength scaling law for the HHG yields.


Electron Matter Interferometry And The Electron Double-Slit Experiment, Roger Bach Apr 2014

Electron Matter Interferometry And The Electron Double-Slit Experiment, Roger Bach

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

Quantum mechanics has fundamentally changed the way scientists think about the world. Quantum mechanical theory has found it's way into our everyday lives through advances in technology. In this dissertation a fundamental quantum mechanical demonstration and the technological development of a new quantum mechanical device are presented.

Double-slit diffraction is a corner stone of quantum mechanics. It illustrates key features of quantum mechanics: interference and the particle-wave duality of matter. Here we demonstrate the full realization of Richard Feynman's famous thought experiment. By placing a movable mask in front of a double-slit to control the transmission through the ...


Gpu Accelerated Long-Term Simulations Of Beam-Beam Effects In Colliders, B. Terzić, V. Morozov, Y. Roblin, F. Lin, H. Zhang, M. Aturban, D. Ranjan, M. Zubair Jan 2014

Gpu Accelerated Long-Term Simulations Of Beam-Beam Effects In Colliders, B. Terzić, V. Morozov, Y. Roblin, F. Lin, H. Zhang, M. Aturban, D. Ranjan, M. Zubair

Computer Science Faculty Publications

We present an update on the development of the new code for long-term simulation of beam-beam effects in particle colliders. The underlying physical model relies on a matrix-based arbitrary-order particle tracking (including a symplectic option) for beam transport and the generalized Bassetti-Erskine approximation for beam-beam interaction. The computations are accelerated through a parallel implementation on a hybrid GPU/CPU platform. With the new code, previously computationally prohibitive long-term simulations become tractable. The new code will be used to model the proposed Medium-energy Electron-Ion Collider (MEIC) at Jefferson Lab.


Diffusive Electron Heat Flow And Temperature Variance Along Magnetic Field Lines, Michael Kushlan Jan 2014

Diffusive Electron Heat Flow And Temperature Variance Along Magnetic Field Lines, Michael Kushlan

Physics Capstone Project

In this research we examine how electron heat moves along magnetic field lines and how this affects temperature variations in plasmas. Specifically we wrote FORTRAN code to solve the electron temperature equation numerically. We also solved the steady state electron temperature equation analytically using an integrating factor. We verified that the numerical and analytical solutions obtained the same result. Finally we calculated the standard deviation of temperature in our domain for the steady state. Gaussian legendre quadrature was used to integrate various functions. We represented our magnetic field and heat source with Fourier series. The sin and cosine coefficients for ...


Dynamical (E,2e) Studies Of Tetrahydropyran And 1,4-Dioxane, J. D. Builth-Williams, G. Da Silva, L. Chiari, D. B. Jones, Hari Chaluvadi, Don H. Madison, M. J. Brunger Jan 2014

Dynamical (E,2e) Studies Of Tetrahydropyran And 1,4-Dioxane, J. D. Builth-Williams, G. Da Silva, L. Chiari, D. B. Jones, Hari Chaluvadi, Don H. Madison, M. J. Brunger

Physics Faculty Research & Creative Works

We present experimental and theoretical results for the electron-impact ionization of the highest occupied molecular orbitals of tetrahydropyran and 1,4-dioxane. Using an (e,2e) technique in asymmetric coplanar kinematics, angular distributions of the slow ejected electron, with an energy of 20 eV, are measured when incident electrons at 250 eV ionize the target and scatter through an angle of either -10° or -15°. The data are compared with calculations performed at the molecular 3-body distorted wave level. Fair agreement between the theoretical model and the experimental measurements was observed. The similar structures for these targets provide key insights for ...


Triply Differential (E,2e) Studies Of Phenol, Silva G. Da, R. F. Neves, L. Chiari, D. B. Jones, E. Ali, Don H. Madison, C. G. Ning, K. L. Nixon, M. C. Lopes, M. J. Brunger Jan 2014

Triply Differential (E,2e) Studies Of Phenol, Silva G. Da, R. F. Neves, L. Chiari, D. B. Jones, E. Ali, Don H. Madison, C. G. Ning, K. L. Nixon, M. C. Lopes, M. J. Brunger

Physics Faculty Research & Creative Works

We have measured (e,2e) triple differential cross sections (TDCS) for the electron-impact ionisation of phenol with coplanar asymmetrical kinematics for an incident electron energy of 250 eV. Experimental measurements of the angular distribution of the slow outgoing electrons at 20 eV are obtained when the incident electron scatters through angles of -5°, -10°, and -15°, respectively. The TDCS data are compared with calculations performed within the molecular 3-body distorted wave model. In this case, a mixed level of agreement, that was dependent on the kinematical condition being probed, was observed between the theoretical and experimental results in the binary ...


Fabrication And Measurements Of 500 Mhz Superconducting Double Spoke Cavity, Hyekyoung Park, C. S. Hopper, J. R. Delayen Jan 2014

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.


Measurement Of Double-Polarization Asymmetries In The Quasielastic ³→He (→E, E' D) Process, M. Mihovilovic, G. Jin, M. Canan, S. Golge, R. Schiavilla, Jefferson Lab Hall A. Collaboration Jan 2014

Measurement Of Double-Polarization Asymmetries In The Quasielastic ³→He (→E, E' D) Process, M. Mihovilovic, G. Jin, M. Canan, S. Golge, R. Schiavilla, Jefferson Lab Hall A. Collaboration

Physics Faculty Publications

We present a precise measurement of double-polarization asymmetries in the ³→He (→e, e' d) reaction. This particular process is a uniquely sensitive probe of hadron dynamics in 3He and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasielastic kinematics at Q2 = 0.25(GeV/c)2 for missing momenta up to 270 MeV/c. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on pm and ω, but are systematically offset. Beyond the region of the quasielastic peak, the discrepancies become even ...


A Compact Beam Spreader Using Rf Deflecting Cavities For The Lcls-Ii, S.U. De Silva, J. R. Delayen, R. G. Olave, L. Doolittle, P. Emma Jan 2014

A Compact Beam Spreader Using Rf Deflecting Cavities For The Lcls-Ii, S.U. De Silva, J. R. Delayen, R. G. Olave, L. Doolittle, P. Emma

Physics Faculty Publications

The LCLS-II project currently under development is designed to accelerate electron bunches up to 4 GeV and transport them to one of two FEL undulators located more than 2 km downstream of the end of the LCLS-II linac. The upgrade requires a spreader system to separate the baseline electron bunches and transport them to two undulator lines or a local dump. Fast bipolar kickers (FK) or transverse electric rf deflectors (RFD) are considered as fast-switching devices (FSD). In the RFD approach described here three design options operating at 325 MHz are studied including a superconducting rf-dipole cavity, a normal conducting ...


Employing Twin Crabbing Cavities To Address Variable Transverse Coupling Of Beams In The Meic, A. Castilla, V. S. Morozov, T. Satogata, J. R. Delayen Jan 2014

Employing Twin Crabbing Cavities To Address Variable Transverse Coupling Of Beams In The Meic, A. Castilla, V. S. Morozov, T. Satogata, J. R. Delayen

Physics Faculty Publications

The design strategy of the Medium Energy Electron-Ion Collider (MEIC) at Jefferson Lab contemplates both matching of the emittance aspect ratios and a 50 mrad crossing angle along with crab crossing scheme for both electron and ion beams over the energy range (√s=20-70 GeV) to achieve high luminosities at the interaction points (IPs). However, the desired locations for placing the crabbing cavities may include regions where the transverse degrees of freedom of the beams are coupled with variable coupling strength that depends on the collider rings’ magnetic elements (solenoids and skew quadrupoles). In this work we explore the feasibility ...


Cryogenic Test Of A 750 Mhz Superconducting Rf Dipole Crabbing Cavity, A. Castilla, Hyekyoung Park, J. R. Delayen Jan 2014

Cryogenic Test Of A 750 Mhz Superconducting Rf Dipole Crabbing Cavity, A. Castilla, Hyekyoung Park, J. R. Delayen

Physics Faculty Publications

A superconducting rf dipole cavity has been designed to address the challenges of a high repetition rate (750 MHz), high current for both electron/ion species (0.5/3 A per bunch), and large crossing angle (50 mrad) at the interaction points (IPs) crabbing system for the Medium Energy Electron-Ion Collider (MEIC) proposed by Jefferson Lab. The cavity prototype built at Niowave, Inc. has been tested at the Jefferson Lab facilities. In this work we present a detailed analysis of the prototype cavity performance at 4 K and 2 K, corroborating the absence of hard multipacting barriers that could limit ...


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 Jan 2014

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 ...


Compilation And Comparison Of Electron Penetration Ranges As A Function Of Effective Number Of Valence Electrons, Teancum Quist Apr 2013

Compilation And Comparison Of Electron Penetration Ranges As A Function Of Effective Number Of Valence Electrons, Teancum Quist

Senior Theses and Projects

The continuous-slow-down approximation (CSDA) is used to create a simple composite analytical formula to estimate the range or maximum penetration depth of bombarding electrons into traditional materials including conductors, semiconductors, and insulators. This formula generates an approximation to the range using a single fitting parameter, Nv, described as the effective number of valence electrons. This applicability of the formulation extends to electrons with energies from 10MeV. These calculations are of great value for studies of high electron bombardment, such as electron spectroscopy or the vacuum of space. A list comprised of 187 materials has been collected that greatly extends ...


Electron Penetration Ranges As A Function Of Effective Number Of Valence Electrons, Teancum Quist, Blake Moore, Greg Wilson, Jr Dennison Apr 2013

Electron Penetration Ranges As A Function Of Effective Number Of Valence Electrons, Teancum Quist, Blake Moore, Greg Wilson, Jr Dennison

Posters

The Continuous-Slow-Down Approximation (CSDA) is used to create a simple composite analytical formula to estimate the range or maximum penetration depth of incident electrons into diverse materials including conductors, semiconductors, and insulators. This formula generates an approximation to the range using a single fitting parameter, Nv, described as the effective number of valence electrons. This range of the formulation extends to electrons with energies from <10 eV to >10MeV, with 20% accuracy. A list comprised of 222 materials has been collected that greatly extends the applicability of this model. Several key material constants were compiled for each material, including the atomic number ...


Electron Transport Models And Precision Measurements In A Constant Voltage Chamber, Justin Dekany, Alec Sim, Jerilyn Brunson, Jr Dennison Jan 2012

Electron Transport Models And Precision Measurements In A Constant Voltage Chamber, Justin Dekany, Alec Sim, Jerilyn Brunson, Jr Dennison

All Physics Faculty Publications

The conductivity of the material is a key transport parameter in spacecraft charging that determines how deposited charge will redistribute throughout the system, how rapidly charge imbalances will dissipate, and what equilibrium potential will be established under given environmental conditions. As the requirements for space missions extend to new regions of space and more stringent requirements are placed on spacecraft performance, it becomes necessary to better understand the underlying conduction mechanisms that determine the dynamic response of insulators to temperature, electric field dose rate, and sample conditioning and history. This study performed detailed measurements of the transient conductivity of representative ...


Electron Induced Luminescence Of Insulating Polymeric Materials, Doug Ball Apr 2011

Electron Induced Luminescence Of Insulating Polymeric Materials, Doug Ball

Senior Theses and Projects

The study of luminescence and electron transport in disordered insulating materials provides detailed information about the material structure and interaction of incident electrons within a material. Electron induced luminescence of insulating polymeric materials has been observed in tests by the USU Materials Physics group. Conduction electrons can transition between extended states in the valence and conduction band and a distribution of localized trapped states within the band gap. Electron transport and luminescence is governed by the distribution of states and transition rates between them. This study investigates the exponentially decaying signatures of both luminescence and sample current of M55J under ...


Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffman, Jr Dennison Jan 2010

Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffman, Jr Dennison

All Physics Faculty Publications

The electron emission properties of a material subject to incident radiation flux are key parameters in determining to what equilibrium charge a spacecraft will established under given environmental conditions. However, there is a complex relation between these emission properties and the charge built up in spacecraft insulators. Complex modeling codes have been developed to predict the potential a spacecraft will adopt as a consequence of its interaction with the space plasma. These require correct models of the electron yields as a function of charge to accurately predict the both the charge build up and the equilibrium potential of spacecraft components ...


Flight Experiments On The Effects Of Contamination On Electron Emission Of Materials, Jr Dennison, Joshua L. Hodges, Jeff Duce, Amberly Evans Jun 2009

Flight Experiments On The Effects Of Contamination On Electron Emission Of Materials, Jr Dennison, Joshua L. Hodges, Jeff Duce, Amberly Evans

All Physics Faculty Publications

We report on a study of the effects of prolonged exposure to the space environment and of chargeenhanced contamination on the electron emission and resistivity of spacecraft materials. The State of Utah Space Environment & Contamination Study (SUSpECS) was deployed on the International Space Station (ISS) in March 2008 onboard the MISSE-6 payload during STS-123. The Materials International Space Station Experiment (MISSE-6) program is designed to characterize the performance of candidate new space materials over the course of its ~17 month exposure to the LEO environment, with a target return date of August 2009 on STS-127. Approximately 165 samples are mounted ...


Low-Fluence Electron Yields Of Highly Insulating Materials, Ryan Hoffmann, Jr Dennison, Clint D. Thomson, Jennifer Albretson Oct 2008

Low-Fluence Electron Yields Of Highly Insulating Materials, Ryan Hoffmann, Jr Dennison, Clint D. Thomson, Jennifer Albretson

Journal Articles

Electron-induced electron yields of high-resistivity, high-yield materials - ceramic polycrystalline aluminum oxide and the polymer polyimide (Kapton HN), - were made by using a low-fluence, pulsed incident electron beam and charge neutralization electron source to minimize charge accumulation. Large changes in energy-dependent total yield curves and yield decay curves were observed, even for incident electron fluences of <3 fC/mm2. The evolution of the electron yield as charge accumulates in the material is modeled in terms of electron re-capture based on an extended Chung-Everhart model of the electron emission spectrum. This model is used to explain anomalies measured in highly insulating, high-yield materials, and ...


Triggering Threshold Spacecraft Charging With Changes In Electron Emission From Materials, Jr Dennison, R. C. Hoffmann, J. Abbott Jan 2007

Triggering Threshold Spacecraft Charging With Changes In Electron Emission From Materials, Jr Dennison, R. C. Hoffmann, J. Abbott

All Physics Faculty Publications

Modest changes in spacecraft charging conditions can lead to abrupt changes in the spacecraft equilibrium, from small positive potentials to large negative potentials relative to the space plasma; this phenomenon is referred to as threshold charging. It is well known that temporal changes of the space plasma environment (electron plasma temperature or density) can cause threshold charging. Threshold charging can also result from by temporal changes in the juxtaposition of the spacecraft to the environment, including spacecraft orbit, orientation, and geometry. This study focuses on the effects of possible changes in electron emission properties of representative spacecraft materials. It is ...