Keyword: brightness
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TUPA86 Simulations of Nanoblade Cathode Emissions with Image Charge Trapping for Yield and Brightness Analyses electron, laser, emittance, scattering 535
  • J.I. Mann, G.E. Lawler, J.B. Rosenzweig, B. Wang
    UCLA, Los Angeles, California, USA
  • T. Arias, J.K. Nangoi
    Cornell University, Ithaca, New York, USA
  • S.S. Karkare
    Arizona State University, Tempe, USA
  Funding: National Science Foundation Grant No. PHY-1549132
Laser-induced field emission from nanostructures as a means to create high brightness electron beams has been a continually growing topic of study. Experiments using nanoblade emitters have achieved peak fields upwards of 40 GV/m according to semi-classical analyses, begging further theoretical investigation. A recent paper has provided analytical reductions of the common semi-infinite Jellium system for pulsed incident lasers. We utilize these results to further understand the physics underlying electron rescattering-type emissions. We numerically evaluate this analytical solution to efficiently produce spectra and yield curves. The effect of space-charge trapping at emission may be simply included by directly modifying these spectra. Additionally, we use a self-consistent 1-D time-dependent Schrödinger equation with an image charge potential to study the same system as a more exact, but computationally costly, approach. With these results we may finally investigate the mean transverse energy and beam brightness at the cathode in these extreme regimes.
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA86  
About • Received ※ 02 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 03 September 2022
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WEPA66 Near-Threshold Photoemission from Graphene Coated Cu Single Crystals electron, cathode, experiment, cryogenics 776
  • C.J. Knill, S.S. Karkare
    Arizona State University, Tempe, USA
  • H. Ago, K. Kawahara
    Global Innovation Center, Kyushu University, Kasuga, Fukuoka, Japan
  • E. Batista, N.A. Moody, G.X. Wang, H. Yamaguchi, P. Yang
    LANL, Los Alamos, New Mexico, USA
  Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams, and by the Department of Energy under Grant DE-SC0021092.
The brightness of electron beams emitted from photocathodes plays a key role in the performance of x-ray free electron lasers (XFELs) and ultrafast electron diffraction (UED) experiments. In order to achieve the maximum beam brightness, the electrons need to be emitted from photocathodes with the smallest possible mean transverse energy (MTE). Recent studies have looked at the effect that a graphene coating has on the quantum efficiency (QE) of the cathode [1]. However, there have not yet been any investigations into the effect that a graphene coating has on the MTE. Here we report on MTE and QE measurements of a graphene coated Cu(110) single crystal cathode at room and cryogenic temperatures. At room temperature, a minimum MTE of 25 meV was measured at 295 nm. This MTE remained stable at 25 meV over several days. At 77 K, the minimum MTE of 9 meV was measured at 290 nm. We perform density functional theory (DFT) calculations to look at the effects of a graphene coating on a Cu(111) surface state. These calculations show that the graphene coating reduces the radius of the surface state, allowing for emission from a lower transverse energy state in comparison to bare Cu(111).
[1] F. Liu et al, Appl. Phys. Lett. 110, 041607 (2017);
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA66  
About • Received ※ 28 July 2022 — Revised ※ 19 July 2022 — Accepted ※ 07 August 2022 — Issue date ※ 10 August 2022
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THYD5 Development of Nanopatterned Strong Field Emission Cathodes cathode, electron, laser, simulation 863
  • G.E. Lawler, N. Majernik, J.I. Mann, N. Montanez, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE HEP Grant DE-SC0009914.
Increasing brightness at the cathode is highly desirable for a diverse suite of applications in the electron accelerator community. These applications range from free electron lasers to ultrafast electron diffraction. Many options for higher brightness cathodes are under investigation notably semiconductor cathodes. We consider here the possibility for an alternative paradigm whereby the cathode surface is controlled to reduce the effective area of illumination and emission. We fabricated nanoblade metallic coated cathodes using common nanofabrication techniques. We have demonstrated that a beam can be successfully extracted with a low emittance and we have reconstructed a portion of the energy spectrum. As a result of our particular geometry, our beam possesses a notably high aspect ratio in its transverse plane. We can now begin to consider modifications for the production of intentionally patterned beams such as higher aspect ratios and hollow beams.
slides icon Slides THYD5 [4.652 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD5  
About • Received ※ 02 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 05 October 2022  
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