IPAC2021 - Classification: MC3: Novel Particle Sources and Acceleration Techniques / T02 Electron Sources

Paper	Title	Page
TUXX01	Review of High Brightness Photoinjectors
	H.J. Qian DESY Zeuthen, Zeuthen, Germany
	High brightness photoinjectors have become the enabling technology in accelerator based light sources, ultrafast electron microscopy, energy recovery linac for ion cooling and many other advanced accelerator concepts. To match the frontiers of these scientific applications, photoinjectors continue to develop for both higher peak and higher average beam brightness. In this review, state of the art photoinjector performances and developments are presented.
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TUXB04	Fabrication and Tuning of a THz-Driven Electron Gun	1297
	S.M. Lewis, A.A. Haase, J.W. Merrick, E.A. Nanni, M.A.K. Othman, S.G. Tantawi SLAC, Menlo Park, California, USA S.M. Lewis Fermilab, Batavia, Illinois, USA
	Funding: This work was supported by the Department of Energy Contract No. DE-AC02-76SF00515 (SLAC) and by NSF Grant No. PHY-1734015. We have developed a THz-driven field emission electron gun and beam characterization assembly. The two cell standing-wave gun operates in the pi mode at 110.08 GHz. It is designed to produce 360 keV electrons with 500 kW of input power supplied by a 110 GHz gyrotron. Multiple gun structures were electroformed in copper using a high precision diamond-turned mandrel. The field emission cathode is a rounded copper tip located in the first cell. The cavity resonances were mechanically tuned using azimuthal compression. This work will discuss details of the fabrication and tuning and present the results of low power measurements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXB04
About •	paper received ※ 18 May 2021 paper accepted ※ 22 June 2021 issue date ※ 28 August 2021
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TUPAB098	Recent Progress Toward a Conduction-Cooled Superconducting Radiofrequency Electron Gun	1604
	O. Mohsen, N. Adams, V. Korampally, A. McKeown, D. Mihalcea, P. Piot, I. Salehinia, N. Tom Northern Illinois University, DeKalb, Illinois, USA R. Dhuley, M.G. Geelhoed, D. Mihalcea, J.C.T. Thangaraj Fermilab, Batavia, Illinois, USA P. Piot ANL, Lemont, Illinois, USA
	Funding: This work was supported by the US Department of Energy (DOE) under contract DE-SC0018367 High-repetition-rate electron sources have widespread applications. This contribution discusses the progress toward a proof-of-principle demonstration for a conduction-cooled electron source. The source consists of a simple modification of an elliptical cavity that enhances the field electric field at the photocathode surface. The source was cooled to cryogenic temperatures and preliminary measurements for the quality factor and accelerating field were performed. Additionally, we present future plans to improve the source along with simulated beam-dynamics performances.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB098
About •	paper received ※ 29 May 2021 paper accepted ※ 17 June 2021 issue date ※ 14 August 2021
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WEPAB097	Initial Nanoblade-Enhanced Laser-Induced Cathode Emission Measurements	2814
	G.E. Lawler, J.I. Mann, J.B. Rosenzweig, V.S. Yu UCLA, Los Angeles, California, USA R.J. Roussel University of Chicago, Chicago, Illinois, 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 Nanostructured photocathodes offer a unique functionality not possible in traditional photocathodes, increasing beam brightness by reducing the effective emission area. Inspired by field emitter tips, we examine a possible extension for higher current operation, an extended nanoblade capable of producing asymmetric emittance electron beams. A full understanding of emission is necessary to establish the effectiveness of nanoblades as usable cathode for electron accelerators. Utilizing wet etching of silicon wafers, we arrive at a robust sample capable of dissipating incident laser fields in excess of 20 GV/m without permanent damage. Initial predictions and experiments from the nanotip case predict energies up to the keV scale from electron rescattering and fine features on the order of the photon quantum. We will present initial electron data from 800 nm Ti:S laser illumination and measurements of a focused 1 keV beam.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB097
About •	paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 26 August 2021
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WEPAB138	Superconducting RF Gun with High Current and the Capability to Generate Polarized Electron Beams	2936
	I. Petrushina SUNY SB, Stony Brook, New York, USA S.A. Belomestnykh, S. Kazakov, T.N. Khabiboulline, M. Martinello, Y.M. Pischalnikov, V.P. Yakovlev Fermilab, Batavia, Illinois, USA J.C. Brutus, P. Inacker, Y.C. Jing, V. Litvinenko, J. Skaritka, E. Wang BNL, Upton, New York, USA J.M. Grames, M. Poelker, R. Suleiman, E.J-M. Voutier JLab, Newport News, Virginia, USA
	High-current low-emittance CW electron beams are indispensable for nuclear and high-energy physics fixed target and collider experiments, cooling high energy hadron beams, generating CW beams of monoenergetic X-rays (in FELs) and gamma-rays (in Compton sources). Polarization of electrons in these beams provides extra value by opening a new set of observables and frequently improving the data quality. We report on the upgrade of the unique and fully functional CW SRF 1.25 MeV SRF gun, built as part of the Coherent electron Cooling (CeC) project, which has demonstrated sustained CW operation with CsK2Sb photocathodes generating electron bunches with record-low transverse emittances and record-high bunch charge exceeding 10 nC. We propose to extend the capabilities of this system to high average current of 100 milliampere in two steps: increasing the current 30-fold at each step with the goal to demonstrate reliable long-term operation of the high-current low-emittance CW SRF guns. We also propose to test polarized GaAs photocathodes in the ultra-high vacuum (UHV) environment of the SRF gun, which has never been successfully demonstrated in RF accelerators.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB138
About •	paper received ※ 25 May 2021 paper accepted ※ 29 July 2021 issue date ※ 23 August 2021
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WEPAB144	A New Flux Concentrator Made of Cu Alloy for the SuperKEKB Positron Source	2954
	Y. Enomoto, K. Abe, N. Okada, T. Takatomi KEK, Ibaraki, Japan
	Flux concentrator (FC) is one of important device for positron source which translates position and momentum spread of the particles adiabatically to match them to the acceptance of the following section. To realize higher positron yield, higher magnetic field is desired. However, higher field by higher current generate stronger force on the coil. Since the gap between each turn of the coil is as narrow as 0.2 mm and the voltage across them is about as high as 1 kV at the design current, slight deformation of the coil cause discharge between the gap. To avoid such problem, a new FC made of Cu alloy which has 40 times higher yield strength than that of pure Cu was designed and tested. Finally, during summer shutdown in 2020, the old FC made of pure Cu was replaced by the new one made of Cu alloy in the KEK electron positron injector linac. The new one has been working stably at the design current, 12 kA, since Oct. 2020, and positron yield of 0.5 was realized. There were no discharge and other trouble till now.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB144
About •	paper received ※ 08 May 2021 paper accepted ※ 01 July 2021 issue date ※ 31 August 2021
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WEPAB147	Simulations of Nanoblade-Enhanced Laser-Induced Cathode Emissions and Analyses of Yield, MTE, and Brightness	2957
	J.I. Mann, G.E. Lawler, J.B. Rosenzweig UCLA, Los Angeles, California, USA T. Arias, J.K. Nangoi Cornell University, Ithaca, New York, 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. Laser-induced field emission of electrons from metallic nanotips has been well studied. Unfortunately, nanotips suffer low damage thresholds with enhanced fields around 10 GV/m. The nanoblade, akin to a nanotip extruded in one lateral dimension, may reach upwards of 40 GV/m due to its robust thermomechanical properties. This increased surface field promises brighter electron emissions. We perform simulations of strong-field emissions from metallic nanoblades via the 1-D time-dependent Schr\"odinger equation with effective Jellium and nonlinear collective image charge potentials, including the strong field gradients induced by the nanostructure. We measure spectra and yields and compare to recent experiments. Potential analytical forms of image potential limited yield for a spectrally rich emission are presented. Calculations of mean transverse energy are provided as well as a prospective method of mitigation with the goal of increasing brightness.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB147
About •	paper received ※ 19 May 2021 paper accepted ※ 06 July 2021 issue date ※ 31 August 2021
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WEPAB148	RF Design of an X-Band TM02 Mode Cavity for Field Emitter Testing	2961
	Z. Li, S.G. Tantawi SLAC, Menlo Park, California, USA S.V. Baryshev, T. Posos, M.E. Schneider Michigan State University, East Lansing, Michigan, USA
	Funding: Work at SLAC was supported by DOE under contract No. DE-AC02-76SF00515. Work at MSU was supported by DOE under Award No. DE-SC0020429 and under Cooperative Agreement Award No. DE-SC0018362. Planar polycrystalline synthetic diamond with nitrogen-doping/incorporation was found to be a remarkable field emitter. It is capable of generating a high charge beam and handling moderate vacuum conditions. Integrating it with an efficient RF cavity could therefore provide a compact electron source for RF injectors. Understanding the performance metrics of the emitter in RF fields is essential toward developing such a device. We investigated a test setup of the field emitter at the X-band frequency. The setup included an X-band cavity operating at the TM02 mode. The field emitter material will be plated on the tip of a insertion rod on the cavity back plate. Part of the back plate and the emitter rod are demountable, allowing for exchange of the field emitters. The TM02 mode was chosen such that the design of the demountable back plate does not induce field enhancement at the installation gap. The cavity were optimized to achieve a high surface field at the emitter tip and a maximum energy gain of the emitted electrons at a given input power. We will present the RF and mechanical design of such a TM02 X-band cavity for field emitter testing.
	Poster WEPAB148 [1.642 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB148
About •	paper received ※ 14 May 2021 paper accepted ※ 12 July 2021 issue date ※ 25 August 2021
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WEPAB149	The RF Gun for the Siberian Circular Light Source "SKIF"	2965
	V. Volkov, A.M. Batrakov, S.M. Gurov, S.E. Karnaev, A.A. Kondakov, S.A. Krutikhin, G.Y. Kurkin, A.E. Levichev, O.I. Meshkov, V.K. Ovchar, A.V. Pavlenko, O.A. Pavlov, A.G. Tribendis, N.G. Vasileva BINP SB RAS, Novosibirsk, Russia A.E. Levichev, A.V. Pavlenko NSU, Novosibirsk, Russia A.G. Tribendis NSTU, Novosibirsk, Russia
	The Siberian Circular Light Source is a new medium-energy high brightness synchrotron light facility that is under construction on the Budker Institute of Nuclear Physics (BINP) in Russia, Novosibirsk. The accelerator facility is divided for convenience into three components; a 3 GeV storage ring, a full-energy booster synchrotron, and a 200 MeV injector linac with a thermionic gridded RF gun electron source. This paper describes the RF gun design and plans for operations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB149
About •	paper received ※ 19 May 2021 paper accepted ※ 07 June 2021 issue date ※ 10 August 2021
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WEPAB152	Carbon Nanotubes as Cold Electron Field Emitters for Electron Cooling in the CERN Extra Low Energy Antiproton (ELENA) Ring	2975
	B. Galante, G. Tranquille CERN, Meyrin, Switzerland O. Apsimon, C.P. Welsch The University of Liverpool, Liverpool, United Kingdom J. Resta-López IFIC, Valencia, Spain
	In ELENA electron cooling reduces the emittance of the antiproton beam allowing to deliver a high-quality beam to the experiments at the unprecedented low energy of 100 keV. To cool the antiproton beam at this low energy, the electron gun must emit electrons with as monoenergetic a distribution as possible. The currently used thermionic gun limits the cooling performance due to the relatively high transverse energy spread of the emitted electrons. Optimization is therefore being studied, aiming at developing a cold-cathode electron gun. This has led to the investigation of carbon nanotubes (CNTs) as cold electron field emitters. CNTs are considered the most promising field emitter material due to their high aspect ratio, chemical stability, and capability to deliver high current densities. To assess the feasibility of using such material operationally a full characterization is required, focussing on key parameters such as emitted current, emission stability, and lifetime. This contribution will present the status of ongoing experiments reporting on the conditioning process necessary to reach good stability over time and the emitting performance of different CNT arrays.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB152
About •	paper received ※ 18 May 2021 paper accepted ※ 25 June 2021 issue date ※ 17 August 2021
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WEPAB157	Understanding the Growth Dynamics Cs-Sb Thin Films via In-Situ Characterization Techniques: Towards Epitaxial Alkali Antimonide Photocathodes	2979
	A. Galdi, I.V. Bazarov, L. Cultrera, J.M. Maxson Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J. Balajka, W.J.I. DeBenedetti, M. Hines, C. Hu, L. Moreschini, H. Paik, C.T. Parzyck, K.M. Shen Cornell University, Ithaca, New York, USA
	Funding: National Science Foundation award PHY-1549132, the Center for Bright Beams and PARADIM, Cooperative Agreement No.DMR-1539918. Alkali antimonide photocathodes, such as Cs3Sb, have attractive properties, such as low emittance and high quantum efficiency, which makes them excellent candidates for next-generation high-brightness electron sources. A large number of studies in literature focus on quantum efficiency and lifetime, and fewer report chemical and structural analysis, despite the latter ultimately determine the brightness at the photocathode. Epitaxial, single-crystalline films would allow to study the intrinsic properties of alkali antimonide photocathodes and to optimize them for maximum brightness, but this goal remains elusive. A strong limiting factor is the extreme air sensitivity, preventing ex-situ structural and chemical analysis. We report a study on the growth of Cs-Sb films via molecular beam epitaxy with reflection high-energy electron diffraction to monitor the growth in real time. The samples were characterized via in-situ ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy and scanning tunneling microscopy. Cs3Sb and CsSb phases can be stabilized on appropriate single crystal substrates, with the latter reproducibly resulting in atomically smooth surfaces.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB157
About •	paper received ※ 19 May 2021 paper accepted ※ 30 June 2021 issue date ※ 01 September 2021
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WEPAB158	Compact Terahertz-Powered Electron Photo-Gun	2983
	T. Kroh, H. Çankaya, U. Demirbas, M. Fakhari, N.H. Matlis, M. Pergament, T. Rohwer CFEL, Hamburg, Germany R.W. Aßmann, H. Dinter, M.J. Kellermeier DESY, Hamburg, Germany M. Hemmer, F.X. Kärtner Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany F.X. Kärtner The Hamburg Center for Ultrafast Imaging, University of Hamburg, Hamburg, Germany
	Funding: This work is supported by the Cluster of Excellence "CUI: Advanced Imaging of Matter" of the Deutsche Forschungsgemeinschaft (DFG) - EXC 2056 - project ID 390715994. Novel accelerator concepts such as all-optical THz based compact accelerators promise to enable new science due to unique features such as reduced timing-jitter and improved space-charge broadening of the generated electron bunches. However, multi-keV electron photo-guns based on short single-cycle THz pulses for acceleration have not been demonstrated experimentally so far. Here, we present a modular THz-driven electron gun with both tunable interaction length and output orifice allowing optimization of the sub-mm interaction volume. First extraction of multi-keV electrons is demonstrated and the parameter space as well as resulting performance of the THz-driven gun by varying the timing of the two single-cycle THz pulses and the UV photo-excitation pulse are explored. Such compact gun prototypes are not only promising as injectors for compact THz-based LINACs but also as source for ultrafast electron diffraction experiments.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB158
About •	paper received ※ 19 May 2021 paper accepted ※ 09 June 2021 issue date ※ 10 August 2021
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WEPAB163	An X-Band Ultra-High Gradient Photoinjector	2986
	S.V. Kuzikov, S.P. Antipov, P.V. Avrakhov, E. Dosov, C.-J. Jing, E.W. Knight Euclid TechLabs, Solon, Ohio, USA G. Ha, C.-J. Jing, W. Liu, P. Piot, J.G. Power, D.S. Scott, J.H. Shao, E.E. Wisniewski ANL, Lemont, Illinois, USA C.-J. Jing Euclid Beamlabs, Bolingbrook, USA X. Lu MIT/PSFC, Cambridge, Massachusetts, USA X. Lu SLAC, Menlo Park, California, USA P. Piot Fermilab, Batavia, Illinois, USA P. Piot, W.H. Tan Northern Illinois University, DeKalb, Illinois, USA E.E. Wisniewski IIT, Chicago, Illinois, USA
	Funding: This work was supported by DoE SBIR grant # DE-SC0018709. High brightness beams appealing for XFELs and UEM essentially imply a high current and a low emittance. To obtain such beams we propose to raise the accelerating voltage in the gun mitigating repealing Coulomb forces. An ultra-high gradient is achieved utilizing a short-pulse technology. We have designed a room temperature X-band 1,5 cell gun that is able to inject 4 MeV, 100 pC bunches with as low as 0.15 mcm normalized transverse emittance. The gun is operated with as high gradients as 400 MV/m and fed by 200 MW, 10 ns RF pulses generated with Argonne Wakefield Accelerator (AWA) power extractor. We report results of low RF power tests, laser alignment test results, and successful gun conditioning results carried out at nominal RF power.
	Poster WEPAB163 [5.427 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB163
About •	paper received ※ 18 May 2021 paper accepted ※ 02 June 2021 issue date ※ 13 August 2021
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WEPAB169	Towards Ultra-Smooth Alkali Antimonide Photocathode Epitaxy	3001
	E.J. Montgomery Private Address, Bolingbrook, USA O. Chubenko, G.S. Gevorkyan, S.S. Karkare, P. Saha Arizona State University, Tempe, USA R.G. Hennig, J.T. Paul University of Florida, Gainesville, Florida, USA C. Jing, S. Poddar Euclid Beamlabs, Bolingbrook, USA H.A. Padmore LBNL, Berkeley, California, USA
	Funding: Work supported by Department of Energy, Office of Science, Office of Basic Energy Sciences, under grant number DE-SC0020575. Photocathodes lead in brightness among electron emitters, but transverse momenta are unavoidably nonzero. Ultra-low transverse emittance would enable brighter, higher energy x-ray free-electron lasers (FEL), improved colliders, and more coherent, detailed ultrafast electron diffraction/microscopy (UED/UEM). Although high quantum efficiency (QE) is desired to avoid laser-induced nonlinearities, the state-of-the-art is 100 pC bunches from copper, 0.4 mm-mrad emittance. Advances towards 0.1 mm-mrad require ultra-low emittance, high QE, cryo-compatible materials. We report efforts towards epitaxial growth of cesium antimonide on lattice matched substrates. DFT calculations were performed to downselect from a list of candidate lattice matches. Co-evaporations achieving >3% QE at 532 nm followed by atomic force and Kelvin probe microscopy (AFM and KPFM) show ultra-low 313 pm rms (root mean square) physical and 2.65 mV rms chemical roughness. We simulate roughness-induced mean transverse energy (MTE) to predict <1 meV from roughness effects at 10 MV/m in as-grown optically thick cathodes, promising low emittance via epitaxial growth.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB169
About •	paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 13 August 2021
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THPAB141	Novel Design of a HVDC Magnetized Electron Source	4034
	O.H. Rahman, J. Skaritka, 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. The hadron beam in EIC is flat with a transverse size ratio of about 1:3. The cooling rate of the hadron beam can be maximized if the electron beam from the strong hadron cooler fully overlaps with the hadron beam. Therefore, generating a flat electron beam is essential. The most efficient way to generate a flat electron beam is to produce a magnetized beam first, and then convert it to flat to the desired transverse size ratio. Using a Magnetized electron beam is a promising way to cool high-energy hadrons. One of the major challenges in producing magnetized beams is fine-tuning the longitudinal magnetic field on the cathode surface and maintaining the desired field uniformity over the emission area. In this paper, we discuss the design of a novel high voltage DC gun capable of fine-tuning the B field on the cathode. This is achieved by installing a permanent magnet inside the cathode puck, with a solenoid field at the front of the cathode. We show magnetostatic simulation to prove the feasibility of this idea. We also show preliminary beam dynamics simulations showing emittance from the gun as the permanent magnet and solenoidal fields are tuned for minimum emittance.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB141
About •	paper received ※ 19 May 2021 paper accepted ※ 02 August 2021 issue date ※ 25 August 2021
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THPAB142	Optical and Surface Characterization of Alkali-Antimonide Photocathodes	4037
	P. Saha, O. Chubenko, G.S. Gevorkyan, A.H. Kachwala, S.S. Karkare, C.J. Knill Arizona State University, Tempe, USA E.J. Montgomery, S. Poddar Euclid Beamlabs, Bolingbrook, USA H.A. Padmore LBNL, Berkeley, California, USA
	Alkali-antimonides, characterized by high quantum efficiency and low mean transverse energy in visible light, are excellent electron sources to drive x-ray free electron lasers, electron cooling and ultrafast electron diffraction applications etc. Existing studies of alkali-antimonides have focused on quantum efficiency and emittance, but information is lacking on the fundamental aspects of the electronic structure, such as the energy gap of the semiconductor and the density of defects as well as the overall nano-structure of the materials. We are, therefore, conducting photoconductivity measurements to measure fundamental semiconductor properties as well as using atomic force microscope (AFM) and kelvin probe force microscope (KPFM) to measure the nanostructure variations in structure and surface potential.
	Poster THPAB142 [1.211 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB142
About •	paper received ※ 16 May 2021 paper accepted ※ 14 July 2021 issue date ※ 15 August 2021
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THPAB145	Cold Test of a Novel S-Band 1.6 Cell Photocathode RF Gun	4045
	Zh.X. Tang, S.X. Dong, Y.J. Pei, B.F. Wei USTC/NSRL, Hefei, Anhui, People’s Republic of China
	Funding: Work supported by National Natural Science Foundation of China(Grant No. 11805199 and U1832135) and Fundamental Research Funds for the Central Universities (Grant No. WK2310000072) The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell cavity with a symmetrical distribution of four grooves is concatenated to the photocathode end of the traditional 0.6 cell cavity to form the novel 0.6 cell cavity. Through the detailed design study, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Considering the filling time, a coupling slot is designed to couple input power into the RF gun. The RF cavity is machined by numerical control machine tool, and the tuning and low power RF measurement are carried out. The experimental results are consistent with the simulation results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB145
About •	paper received ※ 09 May 2021 paper accepted ※ 30 August 2021 issue date ※ 02 September 2021
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THPAB146	Preliminary Study of Femtosecond Electron Source Based on THz Acceleration and Field Emission	4048
	Zh.X. Tang, G. Feng, B.F. Wei USTC/NSRL, Hefei, Anhui, People’s Republic of China
	Funding: Work supported by National Natural Science Foundation of China (Grant No. U1832135 and 11805199) and Fundamental Research Funds for the Central Universities (Grant No. WK2310000072) In this paper, we propose a novel electron gun based on THz acceleration and field emission to generate femtosecond electron bunches. The field emission cathode is placed in the center of the cavity, and the standing wave field is established in the cavity to achieve the field emission conditions and extract the electron beam. Because the period of THz band is about picosecond, the femtosecond bunch is formed by controlling the field strength and the pulse width of the extracted beam. We analyzed the feasibility of field emission and the length of the pulse beam. The surface peak field intensity of the structure of the cavity with different emitters are simulated by CST software.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB146
About •	paper received ※ 09 May 2021 paper accepted ※ 18 August 2021 issue date ※ 02 September 2021
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THPAB151	The Advantage of Cold Electron Source in Electron Diffraction	4053
	J. Liu, H. Luo SWUST, Mianyang City, Sichuan Province, People’s Republic of China
	In this paper, a model for discussing the influence of transverse coherence of electron beams on electron diffraction is established. With reference to Fedele’s thermal-wave model, the transverse coherence length is introduced into this model to characterize the transverse coherence of electron beams. The simulation results show that the transverse coherence of electron beams has a significant influence on electron diffraction, and the cold electron source with high transverse coherence has an obvious advantage in electron diffraction.
	Poster THPAB151 [0.647 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB151
About •	paper received ※ 15 May 2021 paper accepted ※ 21 June 2021 issue date ※ 20 August 2021
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THPAB156	Built-in Thermionic Electron Source for an SRF Linacs	4062
	I.V. Gonin, S. Kazakov, R.D. Kephart, T.N. Khabiboulline, T.H. Nicol, N. Solyak, J.C.T. Thangaraj, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	The design of a thermionic electron source connected directly to a superconducting cavity, the key part of an SRF gun, is described. The results of beam dynamics optimization are presented which allow lack of beam current intercepting in the superconducting cavity. The electron source concept is presented including the cathode-grid assembly, thermal insulation of the cathode from the cavity, and the gun resonator design. The cavity thermal load caused by the gun is analyzed including the static heat load, black body radiation, backward electron heating, etc.
	Poster THPAB156 [0.670 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB156
About •	paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 28 August 2021
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Paper

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TUXX01

Review of High Brightness Photoinjectors

H.J. Qian
DESY Zeuthen, Zeuthen, Germany

High brightness photoinjectors have become the enabling technology in accelerator based light sources, ultrafast electron microscopy, energy recovery linac for ion cooling and many other advanced accelerator concepts. To match the frontiers of these scientific applications, photoinjectors continue to develop for both higher peak and higher average beam brightness. In this review, state of the art photoinjector performances and developments are presented.

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TUXB04

Fabrication and Tuning of a THz-Driven Electron Gun

1297

S.M. Lewis, A.A. Haase, J.W. Merrick, E.A. Nanni, M.A.K. Othman, S.G. Tantawi
SLAC, Menlo Park, California, USA
S.M. Lewis
Fermilab, Batavia, Illinois, USA

Funding: This work was supported by the Department of Energy Contract No. DE-AC02-76SF00515 (SLAC) and by NSF Grant No. PHY-1734015.
We have developed a THz-driven field emission electron gun and beam characterization assembly. The two cell standing-wave gun operates in the pi mode at 110.08 GHz. It is designed to produce 360 keV electrons with 500 kW of input power supplied by a 110 GHz gyrotron. Multiple gun structures were electroformed in copper using a high precision diamond-turned mandrel. The field emission cathode is a rounded copper tip located in the first cell. The cavity resonances were mechanically tuned using azimuthal compression. This work will discuss details of the fabrication and tuning and present the results of low power measurements.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXB04

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paper received ※ 18 May 2021 paper accepted ※ 22 June 2021 issue date ※ 28 August 2021

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TUPAB098

Recent Progress Toward a Conduction-Cooled Superconducting Radiofrequency Electron Gun

1604

O. Mohsen, N. Adams, V. Korampally, A. McKeown, D. Mihalcea, P. Piot, I. Salehinia, N. Tom
Northern Illinois University, DeKalb, Illinois, USA
R. Dhuley, M.G. Geelhoed, D. Mihalcea, J.C.T. Thangaraj
Fermilab, Batavia, Illinois, USA
P. Piot
ANL, Lemont, Illinois, USA

Funding: This work was supported by the US Department of Energy (DOE) under contract DE-SC0018367
High-repetition-rate electron sources have widespread applications. This contribution discusses the progress toward a proof-of-principle demonstration for a conduction-cooled electron source. The source consists of a simple modification of an elliptical cavity that enhances the field electric field at the photocathode surface. The source was cooled to cryogenic temperatures and preliminary measurements for the quality factor and accelerating field were performed. Additionally, we present future plans to improve the source along with simulated beam-dynamics performances.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB098

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paper received ※ 29 May 2021 paper accepted ※ 17 June 2021 issue date ※ 14 August 2021

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WEPAB097

Initial Nanoblade-Enhanced Laser-Induced Cathode Emission Measurements

2814

G.E. Lawler, J.I. Mann, J.B. Rosenzweig, V.S. Yu
UCLA, Los Angeles, California, USA
R.J. Roussel
University of Chicago, Chicago, Illinois, 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
Nanostructured photocathodes offer a unique functionality not possible in traditional photocathodes, increasing beam brightness by reducing the effective emission area. Inspired by field emitter tips, we examine a possible extension for higher current operation, an extended nanoblade capable of producing asymmetric emittance electron beams. A full understanding of emission is necessary to establish the effectiveness of nanoblades as usable cathode for electron accelerators. Utilizing wet etching of silicon wafers, we arrive at a robust sample capable of dissipating incident laser fields in excess of 20 GV/m without permanent damage. Initial predictions and experiments from the nanotip case predict energies up to the keV scale from electron rescattering and fine features on the order of the photon quantum. We will present initial electron data from 800 nm Ti:S laser illumination and measurements of a focused 1 keV beam.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB097

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paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 26 August 2021

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WEPAB138

Superconducting RF Gun with High Current and the Capability to Generate Polarized Electron Beams

2936

I. Petrushina
SUNY SB, Stony Brook, New York, USA
S.A. Belomestnykh, S. Kazakov, T.N. Khabiboulline, M. Martinello, Y.M. Pischalnikov, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
J.C. Brutus, P. Inacker, Y.C. Jing, V. Litvinenko, J. Skaritka, E. Wang
BNL, Upton, New York, USA
J.M. Grames, M. Poelker, R. Suleiman, E.J-M. Voutier
JLab, Newport News, Virginia, USA

High-current low-emittance CW electron beams are indispensable for nuclear and high-energy physics fixed target and collider experiments, cooling high energy hadron beams, generating CW beams of monoenergetic X-rays (in FELs) and gamma-rays (in Compton sources). Polarization of electrons in these beams provides extra value by opening a new set of observables and frequently improving the data quality. We report on the upgrade of the unique and fully functional CW SRF 1.25 MeV SRF gun, built as part of the Coherent electron Cooling (CeC) project, which has demonstrated sustained CW operation with CsK2Sb photocathodes generating electron bunches with record-low transverse emittances and record-high bunch charge exceeding 10 nC. We propose to extend the capabilities of this system to high average current of 100 milliampere in two steps: increasing the current 30-fold at each step with the goal to demonstrate reliable long-term operation of the high-current low-emittance CW SRF guns. We also propose to test polarized GaAs photocathodes in the ultra-high vacuum (UHV) environment of the SRF gun, which has never been successfully demonstrated in RF accelerators.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB138

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paper received ※ 25 May 2021 paper accepted ※ 29 July 2021 issue date ※ 23 August 2021

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WEPAB144

A New Flux Concentrator Made of Cu Alloy for the SuperKEKB Positron Source

2954

Y. Enomoto, K. Abe, N. Okada, T. Takatomi
KEK, Ibaraki, Japan

Flux concentrator (FC) is one of important device for positron source which translates position and momentum spread of the particles adiabatically to match them to the acceptance of the following section. To realize higher positron yield, higher magnetic field is desired. However, higher field by higher current generate stronger force on the coil. Since the gap between each turn of the coil is as narrow as 0.2 mm and the voltage across them is about as high as 1 kV at the design current, slight deformation of the coil cause discharge between the gap. To avoid such problem, a new FC made of Cu alloy which has 40 times higher yield strength than that of pure Cu was designed and tested. Finally, during summer shutdown in 2020, the old FC made of pure Cu was replaced by the new one made of Cu alloy in the KEK electron positron injector linac. The new one has been working stably at the design current, 12 kA, since Oct. 2020, and positron yield of 0.5 was realized. There were no discharge and other trouble till now.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB144

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paper received ※ 08 May 2021 paper accepted ※ 01 July 2021 issue date ※ 31 August 2021

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WEPAB147

Simulations of Nanoblade-Enhanced Laser-Induced Cathode Emissions and Analyses of Yield, MTE, and Brightness

2957

J.I. Mann, G.E. Lawler, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
T. Arias, J.K. Nangoi
Cornell University, Ithaca, New York, 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.
Laser-induced field emission of electrons from metallic nanotips has been well studied. Unfortunately, nanotips suffer low damage thresholds with enhanced fields around 10 GV/m. The nanoblade, akin to a nanotip extruded in one lateral dimension, may reach upwards of 40 GV/m due to its robust thermomechanical properties. This increased surface field promises brighter electron emissions. We perform simulations of strong-field emissions from metallic nanoblades via the 1-D time-dependent Schr\"odinger equation with effective Jellium and nonlinear collective image charge potentials, including the strong field gradients induced by the nanostructure. We measure spectra and yields and compare to recent experiments. Potential analytical forms of image potential limited yield for a spectrally rich emission are presented. Calculations of mean transverse energy are provided as well as a prospective method of mitigation with the goal of increasing brightness.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB147

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paper received ※ 19 May 2021 paper accepted ※ 06 July 2021 issue date ※ 31 August 2021

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WEPAB148

RF Design of an X-Band TM02 Mode Cavity for Field Emitter Testing

2961

Z. Li, S.G. Tantawi
SLAC, Menlo Park, California, USA
S.V. Baryshev, T. Posos, M.E. Schneider
Michigan State University, East Lansing, Michigan, USA

Funding: Work at SLAC was supported by DOE under contract No. DE-AC02-76SF00515. Work at MSU was supported by DOE under Award No. DE-SC0020429 and under Cooperative Agreement Award No. DE-SC0018362.
Planar polycrystalline synthetic diamond with nitrogen-doping/incorporation was found to be a remarkable field emitter. It is capable of generating a high charge beam and handling moderate vacuum conditions. Integrating it with an efficient RF cavity could therefore provide a compact electron source for RF injectors. Understanding the performance metrics of the emitter in RF fields is essential toward developing such a device. We investigated a test setup of the field emitter at the X-band frequency. The setup included an X-band cavity operating at the TM02 mode. The field emitter material will be plated on the tip of a insertion rod on the cavity back plate. Part of the back plate and the emitter rod are demountable, allowing for exchange of the field emitters. The TM02 mode was chosen such that the design of the demountable back plate does not induce field enhancement at the installation gap. The cavity were optimized to achieve a high surface field at the emitter tip and a maximum energy gain of the emitted electrons at a given input power. We will present the RF and mechanical design of such a TM02 X-band cavity for field emitter testing.

Poster WEPAB148 [1.642 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB148

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paper received ※ 14 May 2021 paper accepted ※ 12 July 2021 issue date ※ 25 August 2021

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WEPAB149

The RF Gun for the Siberian Circular Light Source "SKIF"

2965

V. Volkov, A.M. Batrakov, S.M. Gurov, S.E. Karnaev, A.A. Kondakov, S.A. Krutikhin, G.Y. Kurkin, A.E. Levichev, O.I. Meshkov, V.K. Ovchar, A.V. Pavlenko, O.A. Pavlov, A.G. Tribendis, N.G. Vasileva
BINP SB RAS, Novosibirsk, Russia
A.E. Levichev, A.V. Pavlenko
NSU, Novosibirsk, Russia
A.G. Tribendis
NSTU, Novosibirsk, Russia

The Siberian Circular Light Source is a new medium-energy high brightness synchrotron light facility that is under construction on the Budker Institute of Nuclear Physics (BINP) in Russia, Novosibirsk. The accelerator facility is divided for convenience into three components; a 3 GeV storage ring, a full-energy booster synchrotron, and a 200 MeV injector linac with a thermionic gridded RF gun electron source. This paper describes the RF gun design and plans for operations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB149

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paper received ※ 19 May 2021 paper accepted ※ 07 June 2021 issue date ※ 10 August 2021

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WEPAB152

Carbon Nanotubes as Cold Electron Field Emitters for Electron Cooling in the CERN Extra Low Energy Antiproton (ELENA) Ring

2975

B. Galante, G. Tranquille
CERN, Meyrin, Switzerland
O. Apsimon, C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
J. Resta-López
IFIC, Valencia, Spain

In ELENA electron cooling reduces the emittance of the antiproton beam allowing to deliver a high-quality beam to the experiments at the unprecedented low energy of 100 keV. To cool the antiproton beam at this low energy, the electron gun must emit electrons with as monoenergetic a distribution as possible. The currently used thermionic gun limits the cooling performance due to the relatively high transverse energy spread of the emitted electrons. Optimization is therefore being studied, aiming at developing a cold-cathode electron gun. This has led to the investigation of carbon nanotubes (CNTs) as cold electron field emitters. CNTs are considered the most promising field emitter material due to their high aspect ratio, chemical stability, and capability to deliver high current densities. To assess the feasibility of using such material operationally a full characterization is required, focussing on key parameters such as emitted current, emission stability, and lifetime. This contribution will present the status of ongoing experiments reporting on the conditioning process necessary to reach good stability over time and the emitting performance of different CNT arrays.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB152

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paper received ※ 18 May 2021 paper accepted ※ 25 June 2021 issue date ※ 17 August 2021

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WEPAB157

Understanding the Growth Dynamics Cs-Sb Thin Films via In-Situ Characterization Techniques: Towards Epitaxial Alkali Antimonide Photocathodes

2979

A. Galdi, I.V. Bazarov, L. Cultrera, J.M. Maxson
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J. Balajka, W.J.I. DeBenedetti, M. Hines, C. Hu, L. Moreschini, H. Paik, C.T. Parzyck, K.M. Shen
Cornell University, Ithaca, New York, USA

Funding: National Science Foundation award PHY-1549132, the Center for Bright Beams and PARADIM, Cooperative Agreement No.DMR-1539918.
Alkali antimonide photocathodes, such as Cs3Sb, have attractive properties, such as low emittance and high quantum efficiency, which makes them excellent candidates for next-generation high-brightness electron sources. A large number of studies in literature focus on quantum efficiency and lifetime, and fewer report chemical and structural analysis, despite the latter ultimately determine the brightness at the photocathode. Epitaxial, single-crystalline films would allow to study the intrinsic properties of alkali antimonide photocathodes and to optimize them for maximum brightness, but this goal remains elusive. A strong limiting factor is the extreme air sensitivity, preventing ex-situ structural and chemical analysis. We report a study on the growth of Cs-Sb films via molecular beam epitaxy with reflection high-energy electron diffraction to monitor the growth in real time. The samples were characterized via in-situ ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy and scanning tunneling microscopy. Cs3Sb and CsSb phases can be stabilized on appropriate single crystal substrates, with the latter reproducibly resulting in atomically smooth surfaces.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB157

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paper received ※ 19 May 2021 paper accepted ※ 30 June 2021 issue date ※ 01 September 2021

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WEPAB158

Compact Terahertz-Powered Electron Photo-Gun

2983

T. Kroh, H. Çankaya, U. Demirbas, M. Fakhari, N.H. Matlis, M. Pergament, T. Rohwer
CFEL, Hamburg, Germany
R.W. Aßmann, H. Dinter, M.J. Kellermeier
DESY, Hamburg, Germany
M. Hemmer, F.X. Kärtner
Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
F.X. Kärtner
The Hamburg Center for Ultrafast Imaging, University of Hamburg, Hamburg, Germany

Funding: This work is supported by the Cluster of Excellence "CUI: Advanced Imaging of Matter" of the Deutsche Forschungsgemeinschaft (DFG) - EXC 2056 - project ID 390715994.
Novel accelerator concepts such as all-optical THz based compact accelerators promise to enable new science due to unique features such as reduced timing-jitter and improved space-charge broadening of the generated electron bunches. However, multi-keV electron photo-guns based on short single-cycle THz pulses for acceleration have not been demonstrated experimentally so far. Here, we present a modular THz-driven electron gun with both tunable interaction length and output orifice allowing optimization of the sub-mm interaction volume. First extraction of multi-keV electrons is demonstrated and the parameter space as well as resulting performance of the THz-driven gun by varying the timing of the two single-cycle THz pulses and the UV photo-excitation pulse are explored. Such compact gun prototypes are not only promising as injectors for compact THz-based LINACs but also as source for ultrafast electron diffraction experiments.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB158

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paper received ※ 19 May 2021 paper accepted ※ 09 June 2021 issue date ※ 10 August 2021

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WEPAB163

An X-Band Ultra-High Gradient Photoinjector

2986

S.V. Kuzikov, S.P. Antipov, P.V. Avrakhov, E. Dosov, C.-J. Jing, E.W. Knight
Euclid TechLabs, Solon, Ohio, USA
G. Ha, C.-J. Jing, W. Liu, P. Piot, J.G. Power, D.S. Scott, J.H. Shao, E.E. Wisniewski
ANL, Lemont, Illinois, USA
C.-J. Jing
Euclid Beamlabs, Bolingbrook, USA
X. Lu
MIT/PSFC, Cambridge, Massachusetts, USA
X. Lu
SLAC, Menlo Park, California, USA
P. Piot
Fermilab, Batavia, Illinois, USA
P. Piot, W.H. Tan
Northern Illinois University, DeKalb, Illinois, USA
E.E. Wisniewski
IIT, Chicago, Illinois, USA

Funding: This work was supported by DoE SBIR grant # DE-SC0018709.
High brightness beams appealing for XFELs and UEM essentially imply a high current and a low emittance. To obtain such beams we propose to raise the accelerating voltage in the gun mitigating repealing Coulomb forces. An ultra-high gradient is achieved utilizing a short-pulse technology. We have designed a room temperature X-band 1,5 cell gun that is able to inject 4 MeV, 100 pC bunches with as low as 0.15 mcm normalized transverse emittance. The gun is operated with as high gradients as 400 MV/m and fed by 200 MW, 10 ns RF pulses generated with Argonne Wakefield Accelerator (AWA) power extractor. We report results of low RF power tests, laser alignment test results, and successful gun conditioning results carried out at nominal RF power.

Poster WEPAB163 [5.427 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB163

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paper received ※ 18 May 2021 paper accepted ※ 02 June 2021 issue date ※ 13 August 2021

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WEPAB169

Towards Ultra-Smooth Alkali Antimonide Photocathode Epitaxy

3001

E.J. Montgomery
Private Address, Bolingbrook, USA
O. Chubenko, G.S. Gevorkyan, S.S. Karkare, P. Saha
Arizona State University, Tempe, USA
R.G. Hennig, J.T. Paul
University of Florida, Gainesville, Florida, USA
C. Jing, S. Poddar
Euclid Beamlabs, Bolingbrook, USA
H.A. Padmore
LBNL, Berkeley, California, USA

Funding: Work supported by Department of Energy, Office of Science, Office of Basic Energy Sciences, under grant number DE-SC0020575.
Photocathodes lead in brightness among electron emitters, but transverse momenta are unavoidably nonzero. Ultra-low transverse emittance would enable brighter, higher energy x-ray free-electron lasers (FEL), improved colliders, and more coherent, detailed ultrafast electron diffraction/microscopy (UED/UEM). Although high quantum efficiency (QE) is desired to avoid laser-induced nonlinearities, the state-of-the-art is 100 pC bunches from copper, 0.4 mm-mrad emittance. Advances towards 0.1 mm-mrad require ultra-low emittance, high QE, cryo-compatible materials. We report efforts towards epitaxial growth of cesium antimonide on lattice matched substrates. DFT calculations were performed to downselect from a list of candidate lattice matches. Co-evaporations achieving >3% QE at 532 nm followed by atomic force and Kelvin probe microscopy (AFM and KPFM) show ultra-low 313 pm rms (root mean square) physical and 2.65 mV rms chemical roughness. We simulate roughness-induced mean transverse energy (MTE) to predict <1 meV from roughness effects at 10 MV/m in as-grown optically thick cathodes, promising low emittance via epitaxial growth.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB169

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paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 13 August 2021

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THPAB141

Novel Design of a HVDC Magnetized Electron Source

4034

O.H. Rahman, J. Skaritka, 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.
The hadron beam in EIC is flat with a transverse size ratio of about 1:3. The cooling rate of the hadron beam can be maximized if the electron beam from the strong hadron cooler fully overlaps with the hadron beam. Therefore, generating a flat electron beam is essential. The most efficient way to generate a flat electron beam is to produce a magnetized beam first, and then convert it to flat to the desired transverse size ratio. Using a Magnetized electron beam is a promising way to cool high-energy hadrons. One of the major challenges in producing magnetized beams is fine-tuning the longitudinal magnetic field on the cathode surface and maintaining the desired field uniformity over the emission area. In this paper, we discuss the design of a novel high voltage DC gun capable of fine-tuning the B field on the cathode. This is achieved by installing a permanent magnet inside the cathode puck, with a solenoid field at the front of the cathode. We show magnetostatic simulation to prove the feasibility of this idea. We also show preliminary beam dynamics simulations showing emittance from the gun as the permanent magnet and solenoidal fields are tuned for minimum emittance.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB141

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paper received ※ 19 May 2021 paper accepted ※ 02 August 2021 issue date ※ 25 August 2021

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THPAB142

Optical and Surface Characterization of Alkali-Antimonide Photocathodes

4037

P. Saha, O. Chubenko, G.S. Gevorkyan, A.H. Kachwala, S.S. Karkare, C.J. Knill
Arizona State University, Tempe, USA
E.J. Montgomery, S. Poddar
Euclid Beamlabs, Bolingbrook, USA
H.A. Padmore
LBNL, Berkeley, California, USA

Alkali-antimonides, characterized by high quantum efficiency and low mean transverse energy in visible light, are excellent electron sources to drive x-ray free electron lasers, electron cooling and ultrafast electron diffraction applications etc. Existing studies of alkali-antimonides have focused on quantum efficiency and emittance, but information is lacking on the fundamental aspects of the electronic structure, such as the energy gap of the semiconductor and the density of defects as well as the overall nano-structure of the materials. We are, therefore, conducting photoconductivity measurements to measure fundamental semiconductor properties as well as using atomic force microscope (AFM) and kelvin probe force microscope (KPFM) to measure the nanostructure variations in structure and surface potential.

Poster THPAB142 [1.211 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB142

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paper received ※ 16 May 2021 paper accepted ※ 14 July 2021 issue date ※ 15 August 2021

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THPAB145

Cold Test of a Novel S-Band 1.6 Cell Photocathode RF Gun

4045

Zh.X. Tang, S.X. Dong, Y.J. Pei, B.F. Wei
USTC/NSRL, Hefei, Anhui, People’s Republic of China

Funding: Work supported by National Natural Science Foundation of China(Grant No. 11805199 and U1832135) and Fundamental Research Funds for the Central Universities (Grant No. WK2310000072)
The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell cavity with a symmetrical distribution of four grooves is concatenated to the photocathode end of the traditional 0.6 cell cavity to form the novel 0.6 cell cavity. Through the detailed design study, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Considering the filling time, a coupling slot is designed to couple input power into the RF gun. The RF cavity is machined by numerical control machine tool, and the tuning and low power RF measurement are carried out. The experimental results are consistent with the simulation results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB145

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paper received ※ 09 May 2021 paper accepted ※ 30 August 2021 issue date ※ 02 September 2021

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THPAB146

Preliminary Study of Femtosecond Electron Source Based on THz Acceleration and Field Emission

4048

Zh.X. Tang, G. Feng, B.F. Wei
USTC/NSRL, Hefei, Anhui, People’s Republic of China

Funding: Work supported by National Natural Science Foundation of China (Grant No. U1832135 and 11805199) and Fundamental Research Funds for the Central Universities (Grant No. WK2310000072)
In this paper, we propose a novel electron gun based on THz acceleration and field emission to generate femtosecond electron bunches. The field emission cathode is placed in the center of the cavity, and the standing wave field is established in the cavity to achieve the field emission conditions and extract the electron beam. Because the period of THz band is about picosecond, the femtosecond bunch is formed by controlling the field strength and the pulse width of the extracted beam. We analyzed the feasibility of field emission and the length of the pulse beam. The surface peak field intensity of the structure of the cavity with different emitters are simulated by CST software.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB146

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paper received ※ 09 May 2021 paper accepted ※ 18 August 2021 issue date ※ 02 September 2021

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THPAB151

The Advantage of Cold Electron Source in Electron Diffraction

4053

J. Liu, H. Luo
SWUST, Mianyang City, Sichuan Province, People’s Republic of China

In this paper, a model for discussing the influence of transverse coherence of electron beams on electron diffraction is established. With reference to Fedele’s thermal-wave model, the transverse coherence length is introduced into this model to characterize the transverse coherence of electron beams. The simulation results show that the transverse coherence of electron beams has a significant influence on electron diffraction, and the cold electron source with high transverse coherence has an obvious advantage in electron diffraction.

Poster THPAB151 [0.647 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB151

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paper received ※ 15 May 2021 paper accepted ※ 21 June 2021 issue date ※ 20 August 2021

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THPAB156

Built-in Thermionic Electron Source for an SRF Linacs

4062

I.V. Gonin, S. Kazakov, R.D. Kephart, T.N. Khabiboulline, T.H. Nicol, N. Solyak, J.C.T. Thangaraj, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

The design of a thermionic electron source connected directly to a superconducting cavity, the key part of an SRF gun, is described. The results of beam dynamics optimization are presented which allow lack of beam current intercepting in the superconducting cavity. The electron source concept is presented including the cathode-grid assembly, thermal insulation of the cathode from the cavity, and the gun resonator design. The cavity thermal load caused by the gun is analyzed including the static heat load, black body radiation, backward electron heating, etc.

Poster THPAB156 [0.670 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB156

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paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 28 August 2021

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