Author: Biswas, J.P.
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High Voltage DC Gun for High Intensity Polarized Electron Source  
  • O.H. Rahman, J.P. Biswas, C.M. Degen, W. Liu, J. Skarita, E. Wang
    BNL, Upton, New York, USA
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
At Brookhaven National Lab, we have constructed a high intensity polarized electron gun with an inverted electrode geometry and large cathode area. The DC gun showed stable operation at 300 KV with bunch charge up to 16 nC. It also incorporates new technologies such as an active cathode cooling system, a biased anode, and a unique high voltage cable with a semiconductor jacket. Lifetime tests with a biased anode has showed exceptional performance. This gun exceeds EIC polarized gun requirements — high voltage, bunch charge, average current and charge lifetime — with ease. In this talk, we report on the design and performance of the gun including high voltage performance and cathode lifetime tests.
slides icon Slides TUYD1 [2.226 MB]  
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Progress Towards Long-Lifetime, High-Current Polarized-Electron Sources  
  • J.P. Biswas
    Stony Brook University, Stony Brook, USA
  • J.P. Biswas, M. Gaowei, W. Liu, O.H. Rahman, J.T. Sadowski, X. Tong, E. Wang
    BNL, Upton, New York, USA
  Funding: The work was supported by the U.S. Department of Energy under Contract No. DE-AC02-98CH10886
We describe new activation techniques, developed using Cs-Te and Cs-O-Te as a activation layers, to achieve Negative Electron Affinity (NEA) surfaces of GaAs. X-Ray photoelectron spectroscopic and Low Energy Electron Microscopic studies have been performed on these surfaces. The results indicate that both layers achieve NEA of GaAs and lead to longer charge lifetime compared to traditional Cs-O/GaAs photocathodes.
slides icon Slides TUYD2 [10.825 MB]  
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WEPA56 Encapsulation of Photocathodes Using High Power Pulsed RF Sputtering of hBN 760
  • A. Liu, J.R. Callahan, S. Poddar
    Euclid TechLabs, Solon, Ohio, USA
  • J.P. Biswas, M. Gaowei
    BNL, Upton, New York, USA
  Funding: This work is supported by the US DOE SBIR program under contract number DE-SC0021511 and DE-SC0020573.
Photocathodes of various materials are used in photoinjectors for generating photoelectron beams. Of particular interest are the alkali antimonides because of their ultra-high quantum efficiency (QE) and relatively low requirements for growth, and metallic materials such as Cu and Mg which have lower QE but are easier to maintain and have longer lifetime. The biggest challenge of using the alkali antimonide photocathode is that it has an extremely stringent requirement on vacuum and is destroyed rapidly by residual air in the system, while exposure of Mg and Cu in air also impacts the photocathode performance because of the oxidation. The photocathode can be protected against harmful gas molecules by using one or two monolayers of a 2D material such as graphene or hexagonal boron nitride (hBN). Furthermore, hBN monolayers even have the potential to improve the QE of the photocathode when working as the encapsulation thin-film. In this paper, we will discuss the feasibility of coating a photocathode with hBN by high power pulsed RF sputtering by using metallic photocathodes as examples, and compare the performance with encapsulated photocathodes with transferred hBN thin-films.
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA56  
About • Received ※ 31 July 2022 — Revised ※ 04 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 10 August 2022
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WEPA68 Record Quantum Efficiency from Superlattice Photocathode for Spin Polarized Electron Beam Production 784
  • J.P. Biswas, L. Cultrera, K. Kisslinger, W. Liu, J. Skarita, E. Wang
    BNL, Upton, New York, USA
  • S.D. Hawkins, J.F. Klem, S.R. Lee
    Sandia National Laboratories, Albuquerque, New Mexico, USA
  Funding: The work is supported by Brookhaven Science Associates, LLC under Contract DESC0012704 with the U.S. DOE. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
Electron sources producing highly spin-polarized electron beams are currently possible only with photocathodes based on GaAs and other III-V semiconductors. GaAs/GaAsP superlattice (SL) photocathodes with a distributed Bragg reflector (DBR) represent the state of the art for the production of spin-polarized electrons. We present results on a SL-DBR GaAs/GaAsP structure designed to leverage strain compensation to achieve simultaneously high QE and spin polarization. These photocathode structures were grown using molecular beam epitaxy and achieved quantum efficiencies exceeding 15% and electron spin polarization of about 75% when illuminated with near bandgap photon energies.
poster icon Poster WEPA68 [4.506 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA68  
About • Received ※ 20 July 2022 — Revised ※ 02 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 10 August 2022
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