TUYD —  Photon Sources and Electron Accelerators   (09-Aug-22   10:30—12:30)
Chair: Y. Sun, ANL, Lemont, Illinois, USA
Paper Title Page
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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TUYD3 The Quest for the Perfect Cathode 281
  • J.W. Lewellen, J. Smedleypresenter, T. Vecchione
    SLAC, Menlo Park, California, USA
  • D. Filippetto
    LBNL, Berkeley, California, USA
  • S.S. Karkare
    Arizona State University, Tempe, USA
  • J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • P. Musumeci
    UCLA, Los Angeles, California, USA
  Funding: U.S. Department of Energy.
The next generation of free electron lasers will be the first to see the performance of the laser strongly dependent on the materials properties of the photocathode. A new injector proposed for the LCLS-II HE is an example of this revolution, with the goal of increasing the photon energy achievable by LCLS-II to over 20 keV. We must now ask, what is the optimal cathode, temperature, and laser combination to enable this injector? There are many competing requirements. The cathode must be robust enough to operate in a superconducting injector, and must not cause contamination of the injector. It must achieve sufficient charge at high repetition rate, while minimizing the emittance. The wavelength chosen must minimize mean transverse energy while maintaining tolerable levels of multi-photon emission. The cathode must be capable of operating at high (~30 MV/m) gradient, which puts limits on both surface roughness and field emission. This presentation will discuss the trade space for such a cathode/laser combination, and detail a new collaborative program among a variety of institutions to investigate it.
slides icon Slides TUYD3 [1.632 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD3  
About • Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 14 August 2022 — Issue date ※ 26 September 2022
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TUYD4 Towards High Brightness from Plasmon-Enhanced Photoemitters 285
  • C.M. Pierce, I.V. Bazarov, J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • D.B. Durham, D. Filippetto, F. Riminucci
    LBNL, Berkeley, USA
  • A.H. Kachwala, S.S. Karkare
    Arizona State University, Tempe, USA
  • A. Minor
    UC Berkeley, Berkeley, California, USA
  Funding: This work is supported by DOE BES Contract No. DE-AC02-05CH11231. C.P. acknowledges NSF Award PHY-1549132 (CBB) and the US DOE SCGSR program. DD was supported by NSF Grant No. DMR-1548924 (STROBE).
Plasmonic cathodes, whose nanoscale features may locally enhance optical energy from the driving laser trapped at the vacuum interface, have emerged as a promising technology for improving the brightness of metal cathodes. A six orders of magnitude improvement [1] in the non-linear yield of metals has been experimentally demonstrated through this type of nanopatterning. Further, nanoscale lens structures may focus light below its free-space wavelength offering multiphoton photoemission from a region near 10 times smaller [2] than that achievable in typical photoinjectors. In this proceeding, we report on our efforts to characterize the brightness of two plasmonic cathode concepts: a spiral lens and a nanogroove array. We demonstrate an ability to engineer and fabricate nanoscale patterned cathodes by comparing their optical properties with those computed with a finite difference time domain (FDTD) code. The emittance and nonlinear yield of the cathodes are measured under ultrafast laser irradiation. Finally, prospects of this technology for the control and acceleration of charged particle beams are discussed.
[1] Polyakov, A., et al. (2013). Physical Review Letters, 110(7), 076802.
[2] Durham, D. B., et al. (2019). Physical Review Applied, 12(5), 054057.
slides icon Slides TUYD4 [7.160 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD4  
About • Received ※ 05 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 13 September 2022
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TUYD5 Epitaxial Alkali-Antimonide Photocathodes on Lattice-matched Substrates 289
  • P. Saha, S.S. Karkare
    Arizona State University, Tempe, USA
  • E. Echeverria, A. Galdi, J.M. Maxson, C.A. Pennington
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • E.J. Montgomery, S. Poddar
    Euclid Beamlabs, Bolingbrook, USA
  Alkali-antimonides photocathodes, characterized by high quantum efficiency (QE) and low mean transverse energy (MTE) in the visible range of spectrum, are excellent candidates for electron sources to drive X-ray Free Electron Lasers (XFEL) and Ultrafast Electron Diffraction (UED). A key figure of merit for these applications is the electron beam brightness, which is inversely proportional to MTE. MTE can be limited by nanoscale surface roughness. Recently, we have demonstrated physically and chemically smooth Cs3Sb cathodes on Strontium Titanate (STO) substrates grown via co-deposition technique. Such flat cathodes could result from a more ordered growth. In this paper, we present RHEED data of co-deposited Cs3Sb cathodes on STO. Efforts to achieve epitaxial growth of Cs3Sb on STO are then demonstrated via RHEED. We find that films grown epitaxially on substrates like STO and SiC (previously used to achieve single crystalline Cs3Sb) exhibit QE higher than the polycrystalline Cs3Sb cathodes, by an order of magnitude below photoemission threshold. Given the larger QE, lower laser fluence could be used to extract high charge densities, thereby leading to enhanced beam brightness.  
slides icon Slides TUYD5 [2.088 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD5  
About • Received ※ 01 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 07 September 2022
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TUYD6 Design of a 200 kV DC Cryocooled Photoemission Gun for Photocathode Investigations 292
  • G.S. Gevorkyan, T.J. Hanks, A.H. Kachwala, S.S. Karkare, C.J. Knill, C.A. Sarabia Cardenas
    Arizona State University, Tempe, USA
  Funding: This work was supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams, and the DOE under Grant No. DE-SC0021092.
We present the first results of the commissioning of the 200 kV DC electron gun with a cryogenically cooled cathode at Arizona State University. The gun is specifically designed for studying a wide variety of novel cathode materials including single crystalline and epitaxially grown materials at 30 K temperatures to obtain the lowest possible intrinsic emittance of UED and XFEL applications [1]. We will present the measurements of the cryogenic performance of the gun and the first high voltage commissioning results.
[1] G. S. Gevorkyan et. al., Proc. of NAPAC19 MOPLM16 (2019)
slides icon Slides TUYD6 [12.632 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD6  
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 29 September 2022
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