NAPAC2022 - List of Authors (Maxson, J.M.)

Paper	Title	Page
TUYD3	The Quest for the Perfect Cathode	281
	J.W. Lewellen, J. Smedley, 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 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

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, California, 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 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

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 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEZE2	Ultrafast Electron Diffraction at Cornell Using Low Emittance Photocathodes
	J.M. Maxson Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A new system for ultrafast electron diffraction has been commissioned at Cornell which uses alkali antimonides photocathode in a 200 keV DC gun. Utilizing a tunable wavelength ultrafast laser source, it is the first photogun to use near-photoemission-threshold drive laser wavelengths in operation, which provides for very low emittance initial conditions. Emittance is preserved in the space charge regime via emittance compensation in conjunction with multipole correction out to sextupole order. The end result is beam quality that provides the ability to study much smaller material samples (down to a few microns across) or to resolve fine features in diffraction space; these are demonstrated via proof of principle experiments.
	Slides WEZE2 [4.762 MB]
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Paper

Title

Page

The Quest for the Perfect Cathode

281

J.W. Lewellen, J. Smedley, 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 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

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, California, 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 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

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 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEZE2

Ultrafast Electron Diffraction at Cornell Using Low Emittance Photocathodes

J.M. Maxson
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

A new system for ultrafast electron diffraction has been commissioned at Cornell which uses alkali antimonides photocathode in a 200 keV DC gun. Utilizing a tunable wavelength ultrafast laser source, it is the first photogun to use near-photoemission-threshold drive laser wavelengths in operation, which provides for very low emittance initial conditions. Emittance is preserved in the space charge regime via emittance compensation in conjunction with multipole correction out to sextupole order. The end result is beam quality that provides the ability to study much smaller material samples (down to a few microns across) or to resolve fine features in diffraction space; these are demonstrated via proof of principle experiments.

Slides WEZE2 [4.762 MB]

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)