IPAC2018 - List of Authors (Maxson, J.M.)

Paper	Title	Page
TUPML026	Multi-photon Photoemission and Ultrafast Electron Heating in Cu Photocathodes at Threshold	1593
	J. Bae, L. Cultrera Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I.V. Bazarov, J.M. Maxson Cornell University, Ithaca, New York, USA S.S. Karkare, H.A. Padmore LBNL, Berkeley, California, USA P. Musumeci, X.L. Shen UCLA, Los Angeles, California, USA
	Funding: U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams. Operating photocathodes near the photoemission threshold holds the promise of yielding small intrinsic emittance, at the cost of significantly reduced quantum efficiency. In modern femtosecond photoemission electron sources, this requires a very high intensity (10s of GW/cm²) to extract a useful quantity of electrons. At this intensity, the electron occupation function is far from equilibrium and evolves rapidly on sub-ps timescales. Thus, ultrafast laser heating and multiphoton photoemission effects may play a significant role in emission, thereby increasing the minimum achievable emittance. In this work, we use a Boltzmann equation approach to calculate the non-equilibrium occupation function evolution in time for a copper photocathode, yielding a prediction of quantum efficiency and mean transverse energy as a function of input intensity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML026
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TUPML027	Barium Tin Oxide Ordered Photocathodes: First Measurements and Future Perspectives	1597
	A. Galdi, E. B. Lochocki, H. Paik, C.T. Parzyck, D. G. Schlom, K.M. Shen Cornell University, Ithaca, New York, USA G. Adhikari, W.A. Schroeder UIC, Chicago, Illinois, USA I.V. Bazarov, L. Cultrera, W. H. Li, J.M. Maxson, C. M. Pierce Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO₃ with (100) orientation. We demonstrate here the possibility of generating and characterizing electron beams by exciting photoelectrons solely from the conduction band. We report quantum efficiency and mean transverse energy meaurements as a function of photon energy from the bare and Cs-activated La-doped BaSnO₃ surface.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML027
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TUPML028	Photocathodes R&D for High Brightness and Highly Polarized Electron Beams at Cornell University	1601
	L. Cultrera, J. Bae, A.C. Bartnik, I.V. Bazarov, R. Doane, A. Galdi, C.M. Gulliford, W. H. Li, J.M. Maxson, S.A. McBride, T.P. Moore, C. M. Pierce, C. Xu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University is a leader in the development of photocathode materials for the production of high brightness electron beam sources for applications in large scale accelerators and small scale electron scattering experiments. During the last year we have also included Mott polarimetry to investigate long lifetime spin-polarized photocathodes materials. Another thrust of our laboratory is the exploration of ultra low emittance photocathodes at cryogenic temperatures, for which we are building a novel LHe cryogenic electron source. We will review updates from our lab across each of these areas.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML028
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TUPML029	Novel Photocathode Geometry Optimization: Field Enhancing Photoemission Tips	1605
	W. H. Li, I.V. Bazarov, C.M. Gulliford, J.M. Maxson Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams. For photoemission sources, the extraction electric field defines the maximum achievable emission current, and hence the maximum achievable beam brightness. Recently, interest has been growing in studying photocathodes with non-flat geometries to produce local field enhancements in excess of what can be achieved with large area flat cathodes. However, such geometries cause image charge effects which require self-consistent field solvers to correctly simulate. We present a novel simulation framework which combines a full particle in cell field solver (WARP) with a fast adaptive mesh space charge particle tracker (GPT) and a parallel multi-objective genetic optimizer to explore photocathode geometries for ultra high brightnesses. A first application of this technique is also shown, namely the use of field enhanced photoemission tips to create bright beams for ultra-fast electron diffraction.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML029
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THPAF024	Understanding and Compensating Emittance Diluting Effects in Highly Optimized Ultrafast Electron Diffraction Beamlines	3004
	C. M. Pierce, I.V. Bazarov, C.M. Gulliford, J.M. Maxson Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA S. Baturin Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA M.A. Gordon, Y.K. Kim University of Chicago, Chicago, Illinois, USA
	Funding: This work was supported by the Center for Bright Beams, NSF PHY-1549132 and Department of Energy grant DE-SC0014338. The application of Multiobjective Genetic Algorithm optimization (MOGA) to photoemission based ultrafast electron diffraction (UED) beamlines featuring extremely low cathode mean transverse energies has lead to designs with emittances as low as 1 nm for sub-picosecond bunches with 10⁵ electrons*. Analysis of these results shows significant emittance growth during transport: with emittance dilution as high as a factor of 200-4000% for various designs and optics settings. In this study we quantify and model the individual sources of emittance growth (slice mismatches and space charge), and explore the use of the core emittance as a strong invariant. C. Gulliford, A. Bartnik, and I. Bazarov. Multi- objective optimizations of a novel cryocooled dc gun based UED beam line. Phys. Rev. Ac- celerators and Beams, 19(9):093402, 2016.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF024
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THPAK137	Beam-Based Sextupolar Nonlinearity Mapping in CESR	3565
SUSPF067	use link to see paper's listing under its alternate paper code
	L. Gupta, Y.K. Kim University of Chicago, Chicago, Illinois, USA S. Baturin Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA M.P. Ehrlichman, J.M. Maxson, R.E. Meller, D. L. Rubin, D. Sagan, J.P. Shanks Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams In order to maintain beam quality during transport through a storage ring, sextupole magnets are used to make chromatic corrections, but necessarily introduce deleterious effects such as nonlinear resonances and reduced dynamic aperture. Implementing intricate sextupole distributions to mitigate these effects will rely on precision beam-based measurement of the applied sextupole distribution. In this work, we generalize previous sextupole mapping techniques by using resonant phase-locked excitation of the beam at the Cornell Electron Storage Ring (CESR), which accounts for variations in the normal mode tunes on a turn by turn basis. The methods presented here are applied to simulation and actual turn by turn data in CESR for both simplified and realistic sextupole distributions.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK137
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Paper

Title

Page

Multi-photon Photoemission and Ultrafast Electron Heating in Cu Photocathodes at Threshold

1593

J. Bae, L. Cultrera
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I.V. Bazarov, J.M. Maxson
Cornell University, Ithaca, New York, USA
S.S. Karkare, H.A. Padmore
LBNL, Berkeley, California, USA
P. Musumeci, X.L. Shen
UCLA, Los Angeles, California, USA

Funding: U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
Operating photocathodes near the photoemission threshold holds the promise of yielding small intrinsic emittance, at the cost of significantly reduced quantum efficiency. In modern femtosecond photoemission electron sources, this requires a very high intensity (10s of GW/cm²) to extract a useful quantity of electrons. At this intensity, the electron occupation function is far from equilibrium and evolves rapidly on sub-ps timescales. Thus, ultrafast laser heating and multiphoton photoemission effects may play a significant role in emission, thereby increasing the minimum achievable emittance. In this work, we use a Boltzmann equation approach to calculate the non-equilibrium occupation function evolution in time for a copper photocathode, yielding a prediction of quantum efficiency and mean transverse energy as a function of input intensity.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML026

Export •

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

TUPML027

Barium Tin Oxide Ordered Photocathodes: First Measurements and Future Perspectives

1597

A. Galdi, E. B. Lochocki, H. Paik, C.T. Parzyck, D. G. Schlom, K.M. Shen
Cornell University, Ithaca, New York, USA
G. Adhikari, W.A. Schroeder
UIC, Chicago, Illinois, USA
I.V. Bazarov, L. Cultrera, W. H. Li, J.M. Maxson, C. M. Pierce
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO₃ with (100) orientation. We demonstrate here the possibility of generating and characterizing electron beams by exciting photoelectrons solely from the conduction band. We report quantum efficiency and mean transverse energy meaurements as a function of photon energy from the bare and Cs-activated La-doped BaSnO₃ surface.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML027

Export •

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

TUPML028

Photocathodes R&D for High Brightness and Highly Polarized Electron Beams at Cornell University

1601

L. Cultrera, J. Bae, A.C. Bartnik, I.V. Bazarov, R. Doane, A. Galdi, C.M. Gulliford, W. H. Li, J.M. Maxson, S.A. McBride, T.P. Moore, C. M. Pierce, C. Xu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell University is a leader in the development of photocathode materials for the production of high brightness electron beam sources for applications in large scale accelerators and small scale electron scattering experiments. During the last year we have also included Mott polarimetry to investigate long lifetime spin-polarized photocathodes materials. Another thrust of our laboratory is the exploration of ultra low emittance photocathodes at cryogenic temperatures, for which we are building a novel LHe cryogenic electron source. We will review updates from our lab across each of these areas.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML028

Export •

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

TUPML029

Novel Photocathode Geometry Optimization: Field Enhancing Photoemission Tips

1605

W. H. Li, I.V. Bazarov, C.M. Gulliford, J.M. Maxson
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
For photoemission sources, the extraction electric field defines the maximum achievable emission current, and hence the maximum achievable beam brightness. Recently, interest has been growing in studying photocathodes with non-flat geometries to produce local field enhancements in excess of what can be achieved with large area flat cathodes. However, such geometries cause image charge effects which require self-consistent field solvers to correctly simulate. We present a novel simulation framework which combines a full particle in cell field solver (WARP) with a fast adaptive mesh space charge particle tracker (GPT) and a parallel multi-objective genetic optimizer to explore photocathode geometries for ultra high brightnesses. A first application of this technique is also shown, namely the use of field enhanced photoemission tips to create bright beams for ultra-fast electron diffraction.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML029

Export •

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

THPAF024

Understanding and Compensating Emittance Diluting Effects in Highly Optimized Ultrafast Electron Diffraction Beamlines

3004

C. M. Pierce, I.V. Bazarov, C.M. Gulliford, J.M. Maxson
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
S. Baturin
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
M.A. Gordon, Y.K. Kim
University of Chicago, Chicago, Illinois, USA

Funding: This work was supported by the Center for Bright Beams, NSF PHY-1549132 and Department of Energy grant DE-SC0014338.
The application of Multiobjective Genetic Algorithm optimization (MOGA) to photoemission based ultrafast electron diffraction (UED) beamlines featuring extremely low cathode mean transverse energies has lead to designs with emittances as low as 1 nm for sub-picosecond bunches with 10⁵ electrons*. Analysis of these results shows significant emittance growth during transport: with emittance dilution as high as a factor of 200-4000% for various designs and optics settings. In this study we quantify and model the individual sources of emittance growth (slice mismatches and space charge), and explore the use of the core emittance as a strong invariant.
C. Gulliford, A. Bartnik, and I. Bazarov. Multi-
objective optimizations of a novel cryocooled dc gun based
UED beam line. Phys. Rev. Ac-
celerators and Beams, 19(9):093402, 2016.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF024

Export •

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

THPAK137

Beam-Based Sextupolar Nonlinearity Mapping in CESR

3565

SUSPF067

use link to see paper's listing under its alternate paper code

L. Gupta, Y.K. Kim
University of Chicago, Chicago, Illinois, USA
S. Baturin
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
M.P. Ehrlichman, J.M. Maxson, R.E. Meller, D. L. Rubin, D. Sagan, J.P. Shanks
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams
In order to maintain beam quality during transport through a storage ring, sextupole magnets are used to make chromatic corrections, but necessarily introduce deleterious effects such as nonlinear resonances and reduced dynamic aperture. Implementing intricate sextupole distributions to mitigate these effects will rely on precision beam-based measurement of the applied sextupole distribution. In this work, we generalize previous sextupole mapping techniques by using resonant phase-locked excitation of the beam at the Cornell Electron Storage Ring (CESR), which accounts for variations in the normal mode tunes on a turn by turn basis. The methods presented here are applied to simulation and actual turn by turn data in CESR for both simplified and realistic sextupole distributions.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK137

Export •

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