48 results on '"Poelker, Matt"'
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2. Quantum Efficiency Enhancement by Mie Resonance from GaAs Photocathodes Structured with Surface Nanopillar Arrays
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Peng, Xincun, Wang, Zhidong, Liu, Yun, Manos, Dennis M., Poelker, Matt, Stutzman, Marcy, Tang, Bin, Zhang, Shukui, and Zou, Jijun
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Physics - Optics ,Physics - Applied Physics - Abstract
A new type of negative electron affinity (NEA) photocathode based on GaAs nanopillar array (NPA) Mie-type resonators was demonstrated for the first time. For visible wavelengths, the Mie resonances in GaAs NPA reduced light reflectivity to less than 6 percent compared to a typical value great then 35 percent. Other benefits of NPA resonators include an enhanced density of optical states due to increased light concentration and increased electron emission area. These features resulted in improved photoemission performance at the resonance wavelength demonstrating maximum quantum efficiency 3.5 times greater than a GaAs wafer photocathode without the NPA structure. This optically dark photocathode (sub-percentage light reflectance over visible wavelengths) but possessing electrically high-brightness (enhanced electron emission) provides new opportunities for practical applications such as large-scale electron accelerators, high-resolution night-vision imaging and low energy electron microscopy.
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- 2019
3. Non-evaporable getter coating chambers for extreme high vacuum
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Stutzman, Marcy L., Adderley, Philip A., Mamun, Md Abdullah A., and Poelker, Matt
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Physics - Accelerator Physics - Abstract
Techniques for NEG coating a large diameter chamber are presented along with vacuum measurements in the chamber using several pumping configurations, with base pressure as low as 1.56x10^-12 Torr (N2 equivalent) with only a NEG coating and small ion pump. We then describe modifications to the NEG coating process to coat complex geometry chambers for ultra-cold atom trap experiments. Surface analysis of NEG coated samples are used to measure composition and morphology of the thin films. Finally, pressure measurements are compared for two NEG coated polarized electron source chambers: the 130 kV polarized electron source at Jefferson Lab and the upgraded 350 kV polarized 2 electron source, both of which are approaching or within the extreme high vacuum (XHV) range, defined as P<7.5x10^-13 Torr., Comment: Corrected Typos, adjusted table formats
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- 2018
4. Polarized Electron Sources
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Grames, Joe, primary and Poelker, Matt, additional
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- 2022
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5. Photocathodes
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Liu, Wei, Poelker, Matt, Smedley, John, Ganter, Romain, Lee, Young Pak, Series Editor, Lockwood, David J., Series Editor, Ossi, Paolo M., Series Editor, Yamanouchi, Kaoru, Series Editor, Gaertner, Georg, editor, Knapp, Wolfram, editor, and Forbes, Richard G., editor
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- 2020
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6. High figure of merit spin polarized electron sources grown via MOCVD
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Belfore, Benjamin, primary, Masters, Adam, additional, Poudel, Deewakar, additional, Blume, Greg, additional, Polly, Stephen, additional, Wang, Erdong, additional, Hubbard, Seth M, additional, Stutzman, Marcy, additional, Grames, Joseph Michael, additional, Poelker, Matt, additional, Grau, Matt, additional, and Marsillac, Sylvain, additional
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- 2023
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7. Photocathodes
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Liu, Wei, primary, Poelker, Matt, additional, Smedley, John, additional, and Ganter, Romain, additional
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- 2020
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8. GaAs-based superlattice photocathodes manufactured using MOCVD provide spin polarization > 90% and quantum efficiency > 1%
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Poelker, Matt, primary
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- 2023
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9. Non-invasive Polarimetry and Magnetometry
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Roberts, Brock, primary and Poelker, Matt, additional
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- 2018
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10. New Results at JLab Describing Operating Lifetime of GaAs Photo-guns
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Bruker, Max, Grames, Joseph, Hernandez-Garcia, Carlos, Lizárraga-Rubio, Victor, Poelker, Matt, Valerio-Lizárraga, Cristhian, Yoskowitz, Joshua, and Zhang, Shukui
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02: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
Polarized electrons from GaAs photocathodes have been key to some of the highest-impact results of the Jefferson Lab science program over the past 30 years. During this time, various studies have given insight into improving the operational lifetime of these photocathodes in DC high-voltage photo-guns while using lasers with spatial Gaussian profiles of typically 0.5 mm to 1 mm FWHM, cathode voltages of 100 kV to 130 kV, and a wide range of beam currents up to multiple mA. In this contribution, we show recent experimental data from a 100 kV to 180 kV setup and describe our progress at predicting the lifetime based on the calculable dynamics of ionized gas molecules inside the gun. These new experimental studies at Jefferson Lab are specifically aimed at exploring the ion damage of higher-voltage guns being built for injectors., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA
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- 2022
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11. A 500 kV Inverted Geometry Feedthrough for a High Voltage DC Electron Gun
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Hernandez-Garcia, Carlos, Bullard, Don, Grames, Joseph, Palacios Serrano, Gabriel, and Poelker, Matt
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07: Accelerator Technology ,Accelerator Physics - Abstract
The Continuous Electron Beam Accelerator Facility injector at Jefferson Lab (JLab) utilizes an inverted-geometry ceramic insulator photogun operating at 130 kV direct current to generate spin-polarized electron beams for high-energy nuclear physics experiments. A second photogun delivers 180 keV beam for commissioning a SRF booster in a testbed accelerator, and a larger version delivers 300 keV magnetized beam in a test stand beam line. This contribution reports on the development of an unprecedented inverted-insulator with cable connector for reliably applying 500 kV DC to a future polarized beam photogun, to be designed for operating at 350 kV without field emission. Such a photogun design could then be used for generating a polarized electron beam to drive a spin-polarized positron source as a demonstrator for high energy nuclear physics at JLab. There are no commercial cable connectors that fit the large inverted insulators required for that voltage range. Our proposed concept is based on a modified epoxy receptacle with intervening SF6 layer and a test electrode in a vacuum vessel., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA
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- 2022
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12. Improved Electrostatic Design of the Jefferson Lab 300 kV DC Photogun and the Minimization of Beam Deflection
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Mamun, Md Abdullah, Bullard, Don, Delayen, Jean, Grames, Joseph, Hernandez-Garcia, Carlos, Krafft, Geoffrey, Palacios Serrano, Gabriel, Poelker, Matt, Suleiman, Riad, and Wijethunga, Sajini
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06: Beam Instrumentation and Controls ,Accelerator Physics - Abstract
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 gap was reduced to increase the Ez at the photocathode, and the anode aperture was spatially shifted with respect to the beamline longitudinal axis to minimize the beam deflection introduced by the geometric asymmetry of the inverted insulator photogun. The electrostatic design and beam dynamics simulations were performed to determine the required modification. Beam-based measurement from the modified gun confirmed the reduction of the beam deflection, which is presented in this contribution., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA
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- 2022
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13. Concept of a Polarized Positron Source for CEBAF
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Habet, Sami, Bodenstein, Ryan, Bogacz, Alex, Grames, Joseph, Hofler, Alicia, Kazimi, Reza, Lin, Fanglei, Poelker, Matt, Roblin, Yves, Seryi, Andrei, Suleiman, Riad, Sy, Amy, Turner, Dennis, Ushakov, Andriy, Valerio-Lizárraga, Cristhian, and Voutier, Eric
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MC5: Beam Dynamics and EM Fields ,Physics::Accelerator Physics ,Nuclear Experiment ,Accelerator Physics - Abstract
Positron beams would provide new and meaningful probes for the experimental program at the Thomas Jefferson National Accelerator Facility (JLab), including but not limited to future hadronic physics and dark matter experiments. Critical requirements involve generating positron beams with a high degree of spin polarization, sufficient intensity and a continuous-wave (CW) bunch train compatible with acceleration to 12 GeV at the Continuous Electron Beam Accelerator Facility (CEBAF). To address these requirements, a polarized positron injector based upon the bremsstrahlung of an intense CW spin polarized electron beam is considered*. First a polarized electron beam line provides >1 mA of polarized electrons at ~120 MeV to a high-power target for positron production. Next, a second beam line collects, shapes and aligns the spin of positrons for users. Finally, the positron beam is matched into the CEBAF acceptance for acceleration and transport to the end stations with energies up to 12 GeV. An optimized layout to provide positrons beams with intensity >100 nA (polarized) or intensity >3 µA (unpolarized) will be discussed in this poster., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand
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- 2022
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14. High-Gradient Wien Spin Rotators at Jefferson Lab
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Palacios Serrano, Gabriel, Adderley, Philip, Grames, Joseph, Hernandez-Garcia, Carlos, and Poelker, Matt
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02: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
Nuclear physics experiments performed in the Contin-uous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory (JLab) require spin manipulation of electron beams. Two Wien spin rotators in the injector keV region are essential at CEBAF to establish longitudinal polarization at the end station target, and to flip the polarization direction by π rad to rule out false asymmetries. In a Wien filter, the homogeneous and independent electric and magnetic fields, along with the velocity vectors of the electrons that traverse it, form a mutually orthogonal system. The magnitude of the electrostatic field, established by biasing two highly-polished elec-trodes, defines the desired spin angle at the target yet deviates the beam trajectory due to the Lorentz force. The beam trajectory in the Wien is then re-established by adjusting the magnetic field, induced by an electromag-net encasing the device vacuum chamber. This contribu-tion describes the evolution design and high voltage testing of Wien filters for spin manipulation at increased beam energies in the keV injector region, required by high precision parity violation experiments like MOLLER., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA
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- 2022
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15. Operational Experience of the New Booster Cryomodule at the Upgraded Injector Test Facility
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Bruker, Max, Bachimanchi, Ramakrishna, Grames, Joseph, McCaughan, Michael, Musson, John, Owen, Peter, Plawski, Tomasz, Poelker, Matt, Powers, Tom, Wang, Haipeng, and Wang, Yan
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07: Accelerator Technology ,Accelerator Physics - Abstract
Since the early 1990s, the injector of the CEBAF accelerator at Jefferson Lab has relied on a normal-conducting RF graded-beta capture section to boost the kinetic energy of the electron beam from 100 / 130 keV to 600 keV for subsequent acceleration using a cryomodule housing two superconducting 5-cell cavities similar to those used throughout the accelerator. To simplify the injector design and improve the beam quality, the normal-conducting RF capture section and the cryomodule will be replaced with a new single booster cryomodule employing a superconducting, β = 0.6, 2-cell-cavity capture section and a single, β = 0.97, 7-cell cavity. The Upgraded Injector Test Facility at Jefferson Lab is currently hosting the new cryomodule to evaluate its performance with beam before installation at CEBAF. While demonstrating satisfactory performance of the booster and good agreement with simulations, our beam test results also speak to limitations of accelerator operations in a noisy, thermally unregulated environment., Proceedings of the 5th North American Particle Accelerator Conference, NAPAC2022, Albuquerque, NM, USA
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- 2022
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16. Superconducting RF Gun with High Current and the Capability to Generate Polarized Electron Beams
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Petrushina, Irina, Belomestnykh, Sergey, Brutus, Jean Clifford, Grames, Joseph, Inacker, Patrick, Jing, Yichao, Kazakov, Sergey, Khabiboulline, Timergali, Litvinenko, Vladimir, Martinello, Martina, Pischalnikov, Yuriy, Poelker, Matt, Skaritka, John, Suleiman, Riad, Voutier, Eric, Wang, Erdong, and Yakovlev, Vyacheslav
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MC3: Novel Particle Sources and Acceleration Techniques ,Physics::Accelerator Physics ,Accelerator Physics - Abstract
High-current low-emittance CW electron beams are indispensable for nuclear and high-energy physics fixed target and collider experiments, cooling high energy hadron beams, generating CW beams of monoenergetic X-rays (in FELs) and gamma-rays (in Compton sources). Polarization of electrons in these beams provides extra value by opening a new set of observables and frequently improving the data quality. We report on the upgrade of the unique and fully functional CW SRF 1.25 MeV SRF gun, built as part of the Coherent electron Cooling (CeC) project, which has demonstrated sustained CW operation with CsK2Sb photocathodes generating electron bunches with record-low transverse emittances and record-high bunch charge exceeding 10 nC. We propose to extend the capabilities of this system to high average current of 100 milliampere in two steps: increasing the current 30-fold at each step with the goal to demonstrate reliable long-term operation of the high-current low-emittance CW SRF guns. We also propose to test polarized GaAs photocathodes in the ultra-high vacuum (UHV) environment of the SRF gun, which has never been successfully demonstrated in RF accelerators., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil
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- 2021
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17. Improving the Operational Lifetime of the CEBAF Photo-Gun by Anode Biasing
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Yoskowitz, Joshua, Grames, Joseph, Hansknecht, John, Hernandez-Garcia, Carlos, Krafft, Geoffrey, Palacios Serrano, Gabriel, Poelker, Matt, Stutzman, Marcy, Suleiman, Riad, Wijethunga, Sajini, and Van Der Geer, Bas
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MC2: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
The operating lifetime of GaAs-based photocathodes in DC high voltage electron photo-guns is dominated by the ionization rate of residual beamline gas molecules. In this work, experiments were performed to quantify the improvement in photocathode charge lifetime by biasing the photo-gun anode with a positive voltage, which repels ions generated downstream of the anode. The photo-cathode charge lifetime improved by almost a factor of two when the anode was biased compared to the usual grounded configuration. Simulations were performed using the particle tracking code General Particle Tracer (GPT) with a new custom element. The simulation results showed that both the number and energy of ions play a role in the pattern of QE degradation. The experiment results and conclusions supported by GPT simulations will be presented., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil
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- 2021
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18. Space Charge Effects in Low Energy Magnetized Electron Beam
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Wijethunga, Sajini, Benesch, Jay, Delayen, Jean, Krafft, Geoffrey, Mamun, Md Abdullah, Poelker, Matt, Suleiman, Riad, and Zhang, Shukui
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MC5: Beam Dynamics and EM Fields ,Physics::Accelerator Physics ,Accelerator Physics - Abstract
Magnetized electron cooling is one of the major approaches towards obtaining the required high luminosity in the proposed Electron-Ion Collider (EIC). In order to increase the cooling efficiency, a bunched electron beam with a high bunch charge and high repetition rate is required. At Jefferson Lab, we generated magnetized electron beams with high bunch charge using a new compact DC high voltage photogun biased at -300 kV with bialkali-antimonide photocathode and a commercial ultra-fast laser. This contribution discusses how magnetization affects space charge dominated beams as a function of magnetic field strength, gun high voltage, and laser pulse width, and spot size in comparison with simulations performed using General Particle Tracer., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil
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- 2021
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19. Redesign of the Jefferson Lab -300 kV DC Photo-Gun for High Bunch Charge Operations
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Wijethunga, Sajini, Benesch, Jay, Delayen, Jean, Hernandez-Garcia, Carlos, Krafft, Geoffrey, Mamun, Md Abdullah, Palacios Serrano, Gabriel, Poelker, Matt, and Suleiman, Riad
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Physics::Accelerator Physics ,MC2: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
Production of high bunch charge beams for the Electron-Ion Collider (EIC) is a challenging task. High bunch charge (a few nC) electron beam studies at Jefferson Lab using an inverted insulator DC high voltage photo-gun showed evidence of space charge limitations starting at 0.3 nC, limiting the maximum delivered bunch charge to 0.7 nC for beam at -225 kV, 75 ps (FWHM) pulse width, and 1.64 mm (rms) laser spot size. The low extracted charge is due to the modest longitudinal electric field (Ez) at the photocathode leading to beam loss at the anode and downstream beam pipe. To reach the few nC high bunch charge goal, and to correct the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun the existing photo-gun was modified. This contribution discusses the electrostatic design of the modified photo-gun obtained using CST Studio Suite’s electromagnetic field solver. Beam dynamics simulations performed using General Particle Tracer (GPT) with the resulting electrostatic field map obtained from the modified electrodes confirmed the validity of the new design., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil
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- 2021
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20. High Voltage Design and Evaluation of Wien Filters for the CEBAF 200 keV Injector Upgrade
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Palacios Serrano, Gabriel, Adderley, Philip, Baumgart, Helmut, Benesch, Jay, Bullard, Don, Grames, Joseph, Hernandez-Garcia, Carlos, Hofler, Alicia, Machie, Danny, Poelker, Matt, Stutzman, Marcy, and Suleiman, Riad
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Physics::Instrumentation and Detectors ,Physics::Accelerator Physics ,Accelerator Physics ,MC6: Beam Instrumentation, Controls, Feedback and Operational Aspects - Abstract
High-energy nuclear physics experiments at the Jefferson Lab Continuous Electron Beam Accelerator Facility (CEBAF) require highly spin-polarization electron beams, produced from strained super-lattice GaAs photocathodes, activated to negative electron affinity in a photogun operating at 130 kV dc. A pair of Wien filter spin rotators in the injector defines the orientation of the electron beam polarization at the end station target. An upgrade of the CEBAF injector to better support the upcoming MOLLER experiment requires increasing the electron beam energy to 200 keV, to reduce unwanted helicity correlated intensity and position systematics and provide precise control of the polarization orientation. Our contribution describes design, fabrication and testing of the high voltage system to upgrade the Wien spin rotator to be compatible with the 200 keV beam. This required Solidworks modeling, CST and Opera electro- and magnetostatic simulations, upgrading HV vacuum feedthroughs, and assembly techniques for improving electrode alignment. The electric and magnetic fields required by the Wien condition and the successful HV characterization under vacuum conditions are also presented., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil
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- 2021
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21. A comprehensive evaluation of factors that influence the spin polarization of electrons emitted from bulk GaAs photocathodes.
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Wei Liu, Poelker, Matt, Xincun Peng, Shukui Zhang, and Stutzman, Marcy
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GALLIUM arsenide , *PHOTOCATHODES , *SPIN polarization , *QUANTUM efficiency , *CRYSTAL orientation , *PHOTOELECTRON yield - Abstract
The degree of polarization of photoemitted electrons extracted from bulk unstrained GaAs photocathodes is usually considerably less than the theoretical maximum value of 50%, as a result of depolarization mechanisms that originate within the photocathode material and at the vacuum surface interface. This paper provides a comprehensive review of depolarization mechanisms and presents a systematic experimental evaluation of polarization sensitivities to temperature, dopant density, quantum efficiency, and crystal orientation. The highest measured polarization was ~50%, consistent with the maximum theoretical value, obtained from a photocathode sample with relatively low dopant concentration and cooled to 77 K. In general, measurements indicate electron spin polarization can be enhanced at the expense of photoelectron yield (or quantum efficiency). [ABSTRACT FROM AUTHOR]
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- 2017
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22. Lifetime Measurements of GaAs photocathodes at the Upgraded Injector Test Facility at Jefferson Lab*
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Herbert, Maximilian, primary, Enders, Joachim, additional, Poelker, Matt, additional, and Hernandez-Garcia, Carlos, additional
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- 2020
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23. Mie-type GaAs nanopillar array resonators for negative electron affinity photocathodes
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Peng, Xincun, primary, Poelker, Matt, additional, Stutzman, Marcy, additional, Tang, Bin, additional, Zhang, Shukui, additional, and Zou, Jijun, additional
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- 2020
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24. Optical-Resonance-Enhanced Photoemission from Nanostructured GaAs Photocathodes
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Peng, Xincun, primary, Wang, Zhidong, additional, Liu, Yun, additional, Manos, Dennis M., additional, Poelker, Matt, additional, Stutzman, Marcy, additional, Tang, Bin, additional, Zhang, Shukui, additional, and Zou, Jijun, additional
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- 2019
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25. High Current High Charge Magnetized and Bunched Electron Beam from a DC Photogun for JLEIC Cooler
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Zhang, Shukui, Adderley, Philip, Benesch, Jay, Bullard, Don, Delayen, Jean, Grames, Joseph, Guo, Jiquan, Hannon, Fay, Hansknecht, John, Hernandez-Garcia, Carlos, Kazimi, Reza, Krafft, Geoffrey, Mamun, Md Abdullah, Poelker, Matt, Suleiman, Riad, Tiefenback, Michael, Wang, Yan, and Wijethunga, Sajini
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Physics::Accelerator Physics ,MC2: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
A high current, high charge magnetized electron beamline that has been under development for fast and efficient cooling of ion beams for the proposed Jefferson Lab Electron Ion Collider (JLEIC). In this paper, we present the latest progress over the past year that include the generation of picosecond magnetized beam bunches at average currents up to 28 mA with exceptionally long photocathode lifetime, and the demonstrations of magnetized beam with high bunch charge up to 700 pC at 10s of kHz repetition rates. Detailed studies on a stable drive laser system, long lifetime photocathode, beam magnetization effect, beam diagnostics, and a comparison between experiment and simulations will also be reported. These accomplishes marked an important step towards the essential feasibility for the JLEIC cooler design using magnetized beams., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia
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- 2019
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26. The US Electron Ion Collider Accelerator Designs
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Seryi, Andrei, Abell, Dan, Aschenauer, Elke, Barber, Desmond, Bassi, Gabriele, Bazarov, Ivan, Beebe-Wang, Joanne, Bell, George, Benson, Stephen, Berg, J., Blaskiewicz, Michael, Blednykh, Alexei, Bogacz, Alex, Brennan, Joseph, Brindza, Paul, Brooks, Stephen, Brown, Kevin, Bruhwiler, David, Bruker, Max, Cai, Yunhai, Camsonne, Alexandre, Cary, John, Conway, Zachary, Daly, Edward, De Silva, Subashini, Degtiarenko, Pavel, Deitrick, Kirsten, Delayen, Jean, Derbenev, Yaroslav, Diefenthaler, Markus, Dolbeck, Joel, Douglas, David, Drees, Kirsten, Dudnikov, Vadim, Ent, Rolf, Erdelyi, Bela, Fair, Ruben, Fazenbaker, David, Fedotov, Alexei, Fischer, Wolfram, Fox, John, Furletova, Yulia, Gamage, Bamunuvita, Gaskell, David, Gassner, David, Geng, Rong-Li, Gerity, James, Ghoshal, Probir, Gianfelice-Wendt, Eliana, Grames, Joseph, Guo, Jiquan, Guo, Weiming, Hannon, Fay, Hao, Yue, Harwood, Leigh, Henderson, Stuart, Hershcovitch, Ady, Hoffstaetter, Georg, Huang, Haixin, Huang, He, Hutton, Andrew, Hyde, Charles, Jackson, William, Johnson, Rolland, Jordan, Kevin, Kashy, David, Kelly, Michael, Kewisch, Jorg, Kimber, Andrew, Kiselev, Alexander, Krafft, Geoffrey, Lassiter, Ronald, Li, Rui, Lin, Fanglei, Litvinenko, Vladimir, Liu, Chuyu, Lovelace III, Henry, Luo, Yun, Mamun, Md Abdullah, Mann, Thomas, Marhauser, Frank, Mastoridis, Themis, Maxwell, James, McIntyre, Peter, McKeown, Robert, Méot, Francois, Michalski, Tim, Milner, Richard, Minty, Michiko, Montag, Christoph, Morozov, Vasiliy, Musgrave, Matthew, Mustapha, Brahim, Nadel-Turonski, Pawel, Nagaitsev, Sergei, Nissen, Edith, Nosochkov, Yuri, Novokhatski, Alexander, Ostroumov, Peter, Palmer, Robert, Park, Gunn-Tae, Park, HyeKyoung, Parker, Brett, Peggs, Steve, Piot, Philippe, Plastun, Alexander, Poelker, Matt, Pogorelov, Ilya, Pogue, Nathaniel, Powers, Tom, Ptitsyn, Vadim, Qiang, Ji, Rajput-Ghoshal, Renuka, Ranjbar, Vahid, Rimmer, Robert, Robert-Demolaize, Guillaume, Roblin, Yves, Romanov, Dmitry, Roser, Thomas, Rossi, Patrizia, Sabbi, GianLuca, Satogata, Todd, Sattarov, Akhdiyor, Seletskiy, Sergei, Smaluk, Victor, Smith, Kevin, Sosa, Salvador, Spata, Michael, Stupakov, Gennady, Suleiman, Riad, Sullivan, Michael, Sy, Amy, Tennant, Chris, Tepikian, Steven, Terzić, Balsa, Teytelman, Dmitry, Thieberger, Peter, Trbojevic, Dejan, Tsai, Cheng-Ying, Tsoupas, Nicholaos, Wang, Erdong, Wang, Haipeng, Wang, Shaoheng, Weiss, Christian, Weng, Wu-Tsung, Wienands, Ulrich, Willeke, Ferdinand, Wiseman, Mark, Witte, Holger, Wittmer, Walter, Wu, Qiong, Xu, Wencan, York, Richard, Yoshida, Rikutaro, Zaltsman, Alex, Zhang, He, Zhang, Shukui, Zhang, Wu, Zhang, Yuhong, Zhao, Zhiwen, and Zholents, Alexander
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01: Circular and Linear Colliders ,Accelerator Physics - Abstract
With the completion of the National Academies of Sciences Assessment of a US Electron-Ion Collider, the prospects for construction of such a facility have taken a step forward. This paper provides an overview of the two site-specific EIC designs: JLEIC (Jefferson Lab) and eRHIC (BNL) as well as brief overview of ongoing EIC R, Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA
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- 2019
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27. Simulation Study of the Emittance Measurements in Magnetized Electron Beam
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Wijethunga, Sajini, Benesch, Jay, Delayen, Jean, Hannon, Fay, Krafft, Geoffrey, Mamun, Md Abdullah, Palacios Serrano, Gabriel, Poelker, Matt, Suleiman, Riad, and Zhang, Shukui
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MC1: Circular and Linear Colliders ,Physics::Accelerator Physics ,Accelerator Physics - Abstract
Electron cooling of the ion beam is key to obtaining the required high luminosity of proposed electron-ion colliders. For the Jefferson Lab Electron Ion Collider, the expected luminosity of 10³⁴ 〖 cm〗⁻² s⁻¹ will be achieved through so-called ’magnetized electron cooling’, where the cooling process occurs inside a solenoid field, which will be part of the collider ring and facilitated using a circulator ring and Energy Recovery Linac (ERL). As an initial step, we generated magnetized electron beam using a new compact DC high voltage photogun biased at -300 kV employing an alkali-antimonide photocathode. This contribution presents the characterization of the magnetized electron beam (emittance variations with the magnetic field strength for different laser spot sizes) and a comparison to GPT simulations., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia
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- 2019
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28. Status of the Magnetized Thermionic Electron Source at Jefferson Lab
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Hannon, Fay, Bullard, Don, Conway, Joseph, Dunham, Bruce, Eichhorn, Ralf, Gulliford, Colwyn, Hernandez-Garcia, Carlos, Kostroun, Vaclav, Mamun, Md Abdullah, Mayes, Christopher, Poelker, Matt, Smolenski, Karl, Stefani, Mark, Suleiman, Riad, and Taylor, Nicholas
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02: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
A 125kV DC gridded thermionic gun has been de-signed and constructed through a collaboration between Jefferson Lab and Xelera Research LLC. The gun has been recently installed at the Gun Test Stand diagnostic line at Jefferson Lab where transverse and longitudinal parameter space will be experimentally explored. The status and results characterizing the commissioning and trouble-shooting the thermionic gun are presented., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA
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- 2019
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29. Magnetized Electron Source for JLEIC Cooler
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Suleiman, Riad, Adderley, Philip, Benesch, Jay, Bullard, Don, Delayen, Jean, Grames, Joseph, Guo, Jiquan, Hannon, Fay, Hansknecht, John, Hernandez-Garcia, Carlos, Kazimi, Reza, Krafft, Geoffrey, Mamun, Md Abdullah, Poelker, Matt, Tiefenback, Michael, Wang, Yan, Wijethunga, Sajini, Yoskowitz, Joshua, and Zhang, Shukui
- Subjects
03: Novel Particle Sources and Acceleration Techniques ,Physics::Instrumentation and Detectors ,Physics::Accelerator Physics ,Accelerator Physics - Abstract
Magnetized bunched-beam electron cooling is a critical part of the Jefferson Lab Electron Ion Collider (JLEIC). Strong cooling of ion beams will be accomplished inside a cooling solenoid where the ions co-propagate with an electron beam generated from a source immersed in magnetic field. This contribution describes the production and characterization of magnetized electron beam using a compact 300 kV DC high voltage photogun and bialkali-antimonide photocathodes. Beam magnetization was studied using a diagnostic beamline that includes viewer screens for measuring the shearing angle of the electron beamlet passing through a narrow upstream slit. Correlated beam emittance with magnetic field at the photocathode was measured for various laser spot sizes. Measurements of photocathode lifetime were carried out at different magnetized electron beam currents up to 28 mA and high bunch charge up to 0.7 nano-Coulomb was demonstrated., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA
- Published
- 2019
- Full Text
- View/download PDF
30. Operational Results of Simultaneous Four-Beam Delivery at Jefferson Lab
- Author
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Kazimi, Reza, Freyberger, Arne, Grames, Joseph, Hansknecht, John, Hofler, Alicia, Plawski, Tomasz, Poelker, Matt, Spata, Michael, and Wang, Yan
- Subjects
MC2: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
A concept for simultaneous beam delivery to all four CEBAF experimental halls from a single injector and a single main accelerator for the 12 GeV era was proposed in 2012. The original 12 GeV beam delivery plan was for a maximum of three experimental halls at a time as in the 6 GeV era. Therefore, the new concept increases the po-tential beam time for the experiments up to 33%. This change, although a major improvement in operational capabilities, required only limited modifications to the existing machine. The modifications were mainly timing and pattern changes to the beams in the injector, adding a fourth laser to the photo-cathode gun, and the addition of new RF separators to the highest pass of CEBAF. These changes are now complete and, for the first time, the full system is operating, producing four simultaneous beams through the accelerator to four different destinations. In this paper, in addition to presenting the results of the full system commissioning, we will discuss important details about the new configuration plus some of our operational challenges., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia
- Published
- 2019
- Full Text
- View/download PDF
31. Space Charge Study of the Jefferson Lab Magnetized Electron Beam
- Author
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Wijethunga, Sajini, Benesch, Jay, Delayen, Jean, Hannon, Fay, Hernandez-Garcia, Carlos, Krafft, Geoffrey, Mamun, Md Abdullah, Poelker, Matt, Suleiman, Riad, and Zhang, Shukui
- Subjects
Physics::Accelerator Physics ,05: Beam Dynamics and EM Fields ,Accelerator Physics - Abstract
Magnetized electron cooling could result in high luminosity at the proposed Jefferson Lab Electron-Ion Collider (JLEIC). In order to increase the cooling efficiency, a bunched electron beam with high bunch charge and high repetition rate is required. We generated magnetized electron beams with high bunch charge using a new compact DC high voltage photo-gun biased at -300 kV with alkali-antimonide photocathode and a commercial ultrafast laser. This contribution explores how magnetization affects space charge dominated beams as a function of magnetic field strength, gun high voltage, laser pulse width, and laser spot size., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA
- Published
- 2019
- Full Text
- View/download PDF
32. Using a TE011 Cavity as a Magnetic Momentum Monitor
- Author
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Guo, Jiquan, Henry, James, Poelker, Matt, Rimmer, Robert, Suleiman, Riad, and Wang, Haipeng
- Subjects
9. Machine parameters measurements and others ,Physics::Accelerator Physics ,Accelerator Physics - Abstract
The Jefferson Lab Electron-Ion Collider (JLEIC) design relies on cooling of the ion beam with bunched electron beam constrained in a pair of long solenoids. The high current cooling electron beam needs to be generated in a magnetized electron source, and the beam’s magnetization needs to be maintained during the acceleration and transport to the cooling channel. A non-invasive real time monitoring system is highly desired to quantify electron beam magnetization. The authors propose to use a passive copper RF cavity in TE011 mode as such a monitor. In this paper, we present the mechanism and scaling law of this device, as well as the design and preliminary test results of the prototype cavity., Proceedings of the 7\textsuperscript{th} Int. Beam Instrumentation Conf., IBIC2018, Shanghai, China
- Published
- 2019
- Full Text
- View/download PDF
33. Production of Magnetized Electron Beam from a DC High Voltage Photogun
- Author
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Mamun, Md Abdullah, Adderley, Philip, Benesch, Jay, Bullard, Don, Delayen, Jean, Grames, Joseph, Guo, Jiquan, Hannon, Fay, Hansknecht, John, Hernandez-Garcia, Carlos, Kazimi, Reza, Krafft, Geoffrey, Poelker, Matt, Suleiman, Riad, Tiefenback, Michael, Wang, Yan, Wijethunga, Sajini, and Zhang, Shukui
- Subjects
Physics::Accelerator Physics ,02 Photon Sources and Electron Accelerators ,T02 Electron Sources ,Accelerator Physics - Abstract
Bunched-beam electron cooling is a key feature of all proposed designs of the future electron-ion collider, and a requirement for achieving the highest promised collision luminosity. At the Jefferson Lab Electron Ion Collider (JLEIC), fast cooling of ion beams will be accomplished via so-called 'magnetized cooling' implemented using a recirculator ring that employs an energy recovery linac. In this contribution, we describe the production of magnetized electron beam using a compact 300 kV DC high voltage photogun with an inverted insulator geometry, and using alkali-antimonide photocathodes. Beam magnetization was assessed using a modest diagnostic beamline that includes YAG view screens used to measure the rotation of the electron beamlet passing through a narrow upstream aperture. Magnetization results are presented for different gun bias voltages and for different laser spot sizes at the photocathode, using 532 nm lasers with DC and RF time structure. Photocathode lifetime was measured at currents up to 4.5 mA, with and without beam magnetization., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada
- Published
- 2018
- Full Text
- View/download PDF
34. A Non-Invasive Magnetic Momentum Monitor Using a TE011 Cavity
- Author
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Guo, Jiquan, Henry, James, Poelker, Matt, Rimmer, Robert, Suleiman, Riad, and Wang, Haipeng
- Subjects
T03 Beam Diagnostics and Instrumentation ,Physics::Accelerator Physics ,06 Beam Instrumentation, Controls, Feedback, and Operational Aspects ,Accelerator Physics - Abstract
The Jefferson Lab Electron-Ion Collider (JLEIC) design relies on cooling of the ion beam with bunched electron beam. The bunched beam cooler complex consists of a high current magnetized electron source, an energy recovery linac, a circulating ring, and a pair of long solenoids where the cooling takes place. A non-invasive real time monitoring system is highly desired to quantify electron beam magnetization. The authors propose to use a passive copper RF cavity in TE011 mode as such a monitor. In this paper, we will show the mechanism and scaling law of this device, as well as the design and testing results of the prototype cavity., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada
- Published
- 2018
- Full Text
- View/download PDF
35. Negative Electron Affinity Gallium Arsenide Photocathodes Based on Optically Resonant Nanostructure
- Author
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Zhang, Shukui, Peng, Xincun, Poelker, Matt, Stutzman, Marcy, and Zou, Jijun
- Subjects
02 Photon Sources and Electron Accelerators ,T02 Electron Sources ,Accelerator Physics - Abstract
We report the design and fabrication of a new type of negative electron affinity (NEA) gallium arsenide (GaAs) photocathode with optically resonant nanostructures. We observed a significant enhancement of the quantum effi-ciency (QE) from the GaAs photocathode with nanowire arrays (NWA) due to the Mie resonance effect within the intended wavelength range. Theoretical calculations of the expected reflectance behaviour together with experi-mental results of optical and photoemission characteris-tics are presented., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada
- Published
- 2018
- Full Text
- View/download PDF
36. Simulation Study of the Magnetized Electron Beam
- Author
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Wijethunga, Sajini, Benesch, Jay, Delayen, Jean, Hannon, Fay, Krafft, Geoffrey, Mamun, Md Abdullah, Poelker, Matt, and Suleiman, Riad
- Subjects
05 Beam Dynamics and EM Fields ,D09 Emittance Manipulation, Bunch Compression and Cooling ,Physics::Accelerator Physics ,Accelerator Physics - Abstract
Electron cooling of the ion beam plays an important role in electron ion colliders to obtain the required high luminosity. This cooling efficiency can be enhanced by using a magnetized electron beam, where the cooling process occurs inside a solenoid field. This paper compares the predictions of ASTRA and GPT simulations to measurements made using a DC high voltage photogun producing magnetized electron beam, related to beam size and rotation angles as a function of the photogun magnetizing solenoid and other parameters., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada
- Published
- 2018
- Full Text
- View/download PDF
37. Chapter 7 Photocathodes.
- Author
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Wei Liu, Poelker, Matt, Smedley, John, and Ganter, Romain
- Abstract
Photocathodes were at the heart of quantum physics development in the early twentieth century and are still used in high technology devices like nightvision goggles, photomultiplier tubes, and particle accelerators. The simplest form of the photocathode is ametallic surface, negatively biased, from which electrons are extracted by energetic photons. After a brief description of the photocathode preparation, this chapter will present the latest developments and limitations of metallic and semiconductor photocathodes. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
38. Harmonically Resonant Cavity as a Bunch Length Monitor
- Author
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Roberts, Brock, Ali, Mahmoud, Forman, Erica, Grames, Joseph, Hannon, Fay, Kazimi, Reza, Moore, Wesley, Pablo, Melcoy, and Poelker, Matt
- Subjects
Physics::Accelerator Physics ,Charge Monitors and Other Instruments ,Accelerator Physics - Abstract
RF cavities have been designed and constructed that simultaneously and exclusively resonate many harmonic TMono modes. These modes are axially symmetric and have their electric field maximum along the cavities bore. A periodic beam passing through a harmonic cavities bore excites these modes whose superposition can be measured at the cavities antenna with a sampling oscilloscope. Processing the detected waveform with the harmonic cavities transfer function yields the Fourier series of the beam, and a near real-time, non-invasive measurement of the beams longitudinal bunch shape and duration. Experiments have been performed on the 130 kV injector at the Thomas Jefferson National Accelerator Facilities Continuous Electron Beam Accelerator Facility. The harmonic cavities sensitivity was near 1 mV/μA and measured beam bunches ranging in width from 45 to 150 picoseconds (FWHM). These measurements were in close agreement with measurements made using an invasive bunch measurement system as well as predictions by a particle tracking simulations., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain
- Published
- 2017
- Full Text
- View/download PDF
39. Magnetized electron beam for the JLEIC re-circulator cooler ring
- Author
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Poelker, Matt, primary, Adderley, P., additional, Benesch, J., additional, Bullard, B., additional, Grames, J., additional, Hannon, F., additional, Hansknecht, J., additional, Hernandez-Garcia, C., additional, Kazimi, R., additional, Krafft,, G., additional, Mamun, M., additional, Suleiman, R., additional, Tiefenback, M., additional, Wang, Y., additional, Wijiethunga, S., additional, Yoskovitz, J., additional, and Zhang, S., additional
- Published
- 2018
- Full Text
- View/download PDF
40. Nonevaporable getter coating chambers for extreme high vacuum
- Author
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Stutzman, Marcy L., primary, Adderley, Philip A., additional, Mamun, Md Abdullah A., additional, and Poelker, Matt, additional
- Published
- 2018
- Full Text
- View/download PDF
41. Four Beam Generation for Simultaneous Four-Hall Operation at CEBAF
- Author
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Kazimi, Reza, Grames, Joseph, Hansknecht, John, Hofler, Alicia, Lahti, George, Plawski, Tomasz, Poelker, Matt, Suleiman, Riad, and Wang, Yan
- Subjects
Physics::Accelerator Physics ,06 Beam Instrumentation, Controls, Feedback and Operational Aspects ,Accelerator Physics - Abstract
As part of the CEBAF 12 GeV upgrade at Jefferson Lab, a new experimental hall was added to the existing three halls. To deliver beam to all four halls simultaneous-ly, a new timing pattern for electron bunches is needed at the injector. This pattern change has consequences for the frequency of the lasers at the photogun, beam behavior in the chopping system, beam optics due to space charge, and setup procedures. We have successfully demonstrated this new pattern using the three existing drive lasers. The implementation of the full system will occur when the fourth laser is added and upgrades to the Low Level RF (LLRF) are complete. In this paper we explain the new bunch pattern, the challenges for setting and measuring the pattern such as 180° RF phase ambiguity, addition of the fourth laser to the laser table and LLRF upgrade., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea
- Published
- 2016
- Full Text
- View/download PDF
42. A comprehensive evaluation of factors that influence the spin polarization of electrons emitted from bulk GaAs photocathodes
- Author
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Liu, Wei, primary, Poelker, Matt, additional, Peng, Xincun, additional, Zhang, Shukui, additional, and Stutzman, Marcy, additional
- Published
- 2017
- Full Text
- View/download PDF
43. Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes
- Author
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Liu, Wei, primary, Zhang, Shukui, additional, Stutzman, Marcy, additional, and Poelker, Matt, additional
- Published
- 2016
- Full Text
- View/download PDF
44. Observation of Significant Quantum Efficiency Enhancement from a Polarized Photocathode with Distributed Brag Reflector
- Author
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Zhang, Shukui, Chen, Yiqiao, Moy, Aaron, Poelker, Matt, and Stutzman, Marcy
- Subjects
Condensed Matter::Materials Science ,Physics::Instrumentation and Detectors ,Physics::Accelerator Physics ,Physics::Optics ,2: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA
- Published
- 2015
- Full Text
- View/download PDF
45. Vacuum Characterization and Improvement for the Jefferson Lab Polarized Electron Source
- Author
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Stutzman, Marcy, Adderley, Philip, Mamun, Md Abdullah, and Poelker, Matt
- Subjects
7: Accelerator Technology ,Accelerator Physics - Abstract
Operating the JLab polarized electron source with high reliability and long lifetime requires vacuum near the XHV level (, Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA
- Published
- 2015
- Full Text
- View/download PDF
46. PEPPo: Using a Polarized Electron Beam to Produce Polarized Positrons
- Author
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Adeyemi, Adeleke, Adderley, Philip, Ali, Mahmoud, Areti, Hari, Baylac, Maud, Benesch, Jay, Cardman, Lawrence, Clark, Jim, Cole, Phil, Covert, Steve, Cuevas, Chris, Dadoun, Olivier, Dale, Dan, Fanchini, Erica, Forest, Tony, Freyberger, Arne, Froidefond, Emmanuel, Golge, Serkan, Grames, Joseph, Gueye, Paul, Hansknecht, John, Harrell, Percy, Hyde, Charles, Kazimi, Reza, Kim, Yujong, Machie, Danny, Mahoney, Kelly, Mammei, Russell, Marton, Marc, McCarter, James, McCaughan, Michael, Muraz, Jean-Francois, Poelker, Matt, Real, Jean-Sebastien, Stutzman, Marcy, Suleiman, Riad, Tsai, Cheng-Ying, Turner, Dennis, Variola, Alessandro, Voutier, Eric, and Wang, Yan
- Subjects
Physics::Accelerator Physics ,2: Photon Sources and Electron Accelerators ,Accelerator Physics - Abstract
Polarized positron beams have been identified as either an essential or a significant ingredient for the experimental program of both the present and next generation of lepton accelerators (JLab, Super KEK B, ILC, CLIC). An experiment demonstrating a new method for producing polarized positrons has been performed at the Continuous Electron Beam Accelerator Facility at Jefferson Lab. The PEPPo (Polarized Electrons for Polarized Positrons) concept relies on the production of polarized e⁻/e⁺ pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high Z conversion target. PEPPo demonstrated the effective transfer of spin-polarization of an 8.2 MeV/c polarized (P~85%) electron beam to positrons produced in varying thickness tungsten production targets, and collected and measured in the range of 3.1 to 6.2 MeV/c. In comparison to other methods this technique reveals a new pathway for producing either high energy or thermal polarized positron beams using a relatively low polarized electron beam energy (~10MeV) .This presentation will describe the PEPPo concept, the motivations of the experiment and high positron polarization achieved., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA
- Published
- 2015
- Full Text
- View/download PDF
47. Ongoing efforts to construct a 350 kV dc high voltage photogun with inverted insulator geometry
- Author
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Poelker, Matt, primary, Hansknecht, John, additional, and Hernandez-Garcia, Carlos, additional
- Published
- 2016
- Full Text
- View/download PDF
48. Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes
- Author
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Poelker, Matt [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)]
- Published
- 2016
- Full Text
- View/download PDF
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