IPAC2022 - Classification: MC2: Photon Sources and Electron Accelerators / T02: Electron Sources

Paper	Title	Page
THPOST046	CrYogenic Brightness-Optimized Radiofrequency Gun (CYBORG)	2544
SUSPMF021	use link to see paper's listing under its alternate paper code
	G.E. Lawler, A. Fukasawa, N. Majernik, J.R. Parsons, J.B. Rosenzweig, Y. Sakai, A. Suraj UCLA, Los Angeles, California, USA
	Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE Contract DE-SC0020409 Producing higher brightness beams at the cathode is one of the main focuses for future electron beam applications. For photocathodes operating close to their emission threshold, the cathode lattice temperature begins to dominate the minimum achievable intrinsic emittance. At UCLA, we are designing a radiofrequency (RF) test bed for measuring the temperature dependence of the mean transverse energy (MTE) and quantum efficiency for a number of candidate cathode materials. We intend to quantify the attainable brightness improvements at the cathode from cryogenic operation and establish a proof-of-principle cryogenic RF gun for future studies of a 1.6-cell cryogenic photoinjector for the UCLA ultra compact XFEL concept (UC-XFEL). The test bed will use a C-band 0.5-cell RF gun designed to operate down to 45 K, producing an on-axis accelerating field of 120 MV/m. The cryogenic system uses conduction cooling and a load-lock system is being designed for transport and storage of air-sensitive high brightness cathodes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOST046
About •	Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 01 July 2022
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THPOPT005	Field Enhanced, Compact S-Band Gun Employing a Pin Cathode	2567
SUSPMF020	use link to see paper's listing under its alternate paper code
	R. Bazrafshan, T. Rohwer Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany M. Fakhari, K. Flöttmann, F.X. Kaernter DESY, Hamburg, Germany N.H. Matlis CFEL, Hamburg, Germany
	S-band RF-guns are highly developed for production of low emittance relativistic electron bunches, but need powerful klystrons for driving. Here, we present the design and first experimental tests of a compact S-band gun, which can accelerate electrons up to 180 keV powered by only 10 kW from a compact rack-mountable solid-state amplifier. A pin-cathode is used to enhance the RF electric field on the cathode up to 100 MV/m as in large-scale S-band guns. An electron bunch is generated through photoemission off a flat copper surface on the pin excited by a UV laser pulse followed by a focusing solenoid producing a low emittance bunch with 0.1 mm mrad transverse emittance for up to 100 fC bunch charge. We are currently in the conditioning phase of the gun and first experiments show good agreement with simulations. The compact gun will serve three purposes: (i) it can be used directly for ultrafast electron diffraction; (ii) as an injector into a THz booster producing 0.3MeV to 2 MeV electron bunches for ultrafast electron diffraction; (iii) The system in (ii) serves as an injector into a THz linear accelerator producing a 20 MeV beam for the AXSIS X-ray source project.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT005
About •	Received ※ 21 May 2022 — Revised ※ 12 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 10 July 2022
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THPOPT019	Multi-Alkali Antimonide Photocathode Development for High Brightness Beams	2610
	S. Mistry, T. Kamps, J. Kühn, C. Wang HZB, Berlin, Germany T. Kamps HU Berlin, Berlin, Germany C. Wang University Siegen, Siegen, Germany
	Funding: This work is funded by the DFG CO 1509/10-1 \| MI 2917/1-1 Photocathode R&D at the Helmholtz-Zentrum Berlin (HZB) is driven by the motivation to produce high brightness electron beams for the SRF photoinjector test facility, Sealab/ bERLinPro. Multi-alkali antimonides are the choice photocathode material due to high quantum efficiency (QE) and low intrinsic emittance in the visible range. In this work a more robust alternative to the tried and tested Cs-K-Sb is considered. Na-K-Sb offers similar advantages to Cs-K-Sb including, high QE at green wavelengths but moreover, it offers excellent stability at elevated temperatures. This property could lengthen the cathode lifetime by enhancing the robustness of the photocathode inside the SRF gun. In this work, a status report showcasing first results towards the development of a growth procedure for Na-K-Sb is presented by means of spectral response and XPS measurements conducted in the HZB photocathode lab.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT019
About •	Received ※ 03 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 04 July 2022
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THPOPT020	Status and Plans for the New CLS Electron Source Lab	2614
	M.J. Boland, D. Bertwistle, F. Le Pimpec CLS, Saskatoon, Saskatchewan, Canada X.F.D. Stragier TUE, Eindhoven, The Netherlands
	The Canadian Light Source (CLS) has recently created a new Electron Source Lab (ESL) that can run independently from user operations. A section of the old Saskatchewan Accelerator Laboratory experimental nuclear physics tunnels has been rebuilt with new shielding and a separate entrance. The laboratory will be used to prepare an operational spare electron gun for the 250 MeV linac. In addition, there are plans to develop RF guns for a future branch line to inject into the linac and for possible short pulse production. This paper will give an overview of the ESL space and the first electron guns which plan to be installed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT020
About •	Received ※ 16 June 2022 — Revised ※ 29 June 2022 — Accepted ※ 04 July 2022 — Issue date ※ 08 July 2022
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THPOPT022	Study on QE Evolution of Cs₂Te Photocathodes in ELBE SRF Gun-II	2617
	R. Xiang, A. Arnold, S. Ma, P. Michel, P. Murcek, A.A. Ryzhov, J. Schaber, J. Teichert, P.Z. Zwartek HZDR, Dresden, Germany
	The quality of the photocathodes is critical for the sta-bility and reliability of the photoinjector’s operation. Thanks to the robust magnesium and Cs₂Te photocathodes, SRF gun-II at HZDR has been proven to be a suc-cessful example in CW mode for high current user operation. In this contribution, we will present our observation of the QE evolution of Cs₂Te photocathodes during SRF gun operation. The variables including substrate surface, film thickness, Cs/Te stoichiometric, multipacting, RF loading and charge extract are considered in the analysis.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT022
About •	Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 06 July 2022
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THPOPT024	MIST - The MESA-Injector Source Two	2624
	M.A. Dehn, P.S. Plattner IKP, Mainz, Germany K. Aulenbacher HIM, Mainz, Germany K. Aulenbacher GSI, Darmstadt, Germany K. Aulenbacher KPH, Mainz, Germany
	Funding: Work supported by the German science ministry BMBF through Verbundforschung The new accelerator MESA (Mainz Energy Recovering Superconducting Accelerator) will provide an average CW electron beam current of up to 10 mA. Operating at 1.3 GHz, this corresponds to a bunch charge of 7.7 pC. The new DC photoemission source MIST is optimized for these requirements. A challenge is heating of the photocathode at high laser power. By a suitable mechanical construction and the use of specific materials, the heat can be dissipated during operation. Options for further improvements are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT024
About •	Received ※ 07 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 01 July 2022
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THPOPT025	Photocathode Stress Test Bench at INFN LASA	2627
	D. Sertore, D. Giove, L. Monaco INFN/LASA, Segrate (MI), Italy A. Bacci, F. Canella, S. Cialdi, I. Drebot, D. Giannotti, L. Serafini INFN-Milano, Milano, Italy D. Cipriani, E. Suerra Università degli Studi di Milano, Milano, Italy G. Galzerano POLIMI, Milano, Italy G. Guerini Rocco Università degli Studi di Milano & INFN, Segrate, Italy
	A UHV test bench based on a 100 kV DC gun and a 100 MHz repetition rate laser has been setup up at INFN LASA to test Cs₂Te photocathodes. This operation mode is the baseline of the BriXSinO project, currently in the design phase in our laboratory, and the qualification of the Cs₂Te photocathodes is a key issue. In this paper, we present the recent advances in the different aspects of this R&D activity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT025
About •	Received ※ 10 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 20 June 2022
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THPOPT026	Assembly and Characterization of Low-Energy Electron Transverse Momentum Measurement Device (TRAMM) at INFN LASA	2630
	D. Sertore, M. Bertucci, A. Bosotti, D. Giove, L. Monaco, R. Paparella INFN/LASA, Segrate (MI), Italy G. Guerini Rocco, C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	In the framework of high-brightness electron beam generation, thermal emittance is nowadays a key parameter. While alkali tellurides are extensively used in advanced electron sources, alkali antimonides photocathodes demonstrated high QE in the visible, thus making feasible CW operations for RF-based photoinjectors. The INFN LASA laboratory in Milan is fully equipped with dedicated production systems for photocathode preparation and optical setup for QE evaluation. In this paper, we describe a newly designed device dedicated to electron transverse momentum measurement (TRAMM). It will be connected to the main production chambers and will serve as an "emittance monitoring" system during photocathode growth. From the design phase, through the parameter estimate, assembly of the components, to the installation and first measurements, we describe the status of this project and its future developments.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT026
About •	Received ※ 09 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 07 July 2022
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THPOPT027	R&D on High QE Photocathodes at INFN LASA	2633
	D. Sertore, M. Bertucci, L. Monaco INFN/LASA, Segrate (MI), Italy G. Guerini Rocco Università degli Studi di Milano & INFN, Segrate, Italy S.K. Mohanty, H.J. Qian, F. Stephan DESY Zeuthen, Zeuthen, Germany
	We present the recent activities on antimonide and telluride alkali based photocathodes at INFN LASA. The R&D on Cs₂Te materials is focused on investigating effects of material thickness and growth procedures on the photocathodes performances during operation in RF guns. We aim to improve thermal emittance and long term stability of these films. The more recent work on alkali antimonide showed the need for substantial improvements in stability and QE during operation. We present here our recent achievements and plans for future activities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT027
About •	Received ※ 09 June 2022 — Revised ※ 16 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022
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THPOPT028	Dependence of CsK2Sb Photocathode Performance on the Quality of Graphene Substrate Film	2637
	L. Guo, K. Goto, Y. Takashima Nagoya University, Nagoya, Japan H. Yamaguchi LANL, Los Alamos, New Mexico, USA M. Yamamoto KEK, Ibaraki, Japan
	Funding: U.S.-Japan Science and Technology Cooperation Program in High Energy Physics A photocathode that extracts electrons by irradiating a semiconductor or metal with a laser is applied to advanced accelerators and electron microscopes as a high-performance cathode. In particular, the CsK2Sb photocathode is of interest because it has features such as low emittance, excitability with visible light, and high quantum efficiency. Generally, the CsK2Sb photocathode is produced by depositing a cathode element on a substrate, so that the cathode performance strongly depends on the surface condition of the substrate. We have found graphene as reusable substrate, which has the property of being chemically inactive. In this study, graphene film quality dependence of CsK2Sb photo-cathode performance was evaluated. Specifically, CsK2Sb cathode was deposited using different quality graphene film substrates and their QE values and uniformity were compared. The quality of graphene films was analyzed using X-ray Photoelectron Spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). We found that the graphene film can be cleaned by heating at 500 deg. The QE of the cathode on a good quality graphene film was higher and more uniform than that on a poor quality graphene film.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT028
About •	Received ※ 16 May 2022 — Revised ※ 10 June 2022 — Accepted ※ 10 June 2022 — Issue date ※ 24 June 2022
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THPOPT029	Study on the Performance Improvement of Alkali Antimonide Photocathodes for Radio Frequency Electron Guns	2640
	R. Fukuoka, K. Ezawa, Y. Koshiba, M. Washio Waseda University, Tokyo, Japan K. Sakaue The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan
	Semiconductor photocathodes such as Cs-Te and Cs-K-Sb are used as electron sources in accelerators to generate high brightness beams using radio frequency (rf) electron guns. Alkali antimonide photocathodes have a high quantum efficiency (Q.E.) of ~10%, and their excitation wavelength is in the visible light region (532 nm), so that they are expected to reduce the requirements on the optical system and increase the amount of charge compared to Cs-Te. However, alkali antimonide photocathodes have a short lifetime and degrade under poor vacuum conditions, so it is essential to improve durability by protective film coatings. Therefore, we are currently working on the fabrication of high Q.E. alkali antimonide photocathodes that can withstand the Q.E. reduction during coating. In this presentation, we will report the results of comparison between the fabricated alkali antimonide photocathode and Cs-Te photocathode, and future prospects.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT029
About •	Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 09 July 2022
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THPOPT030	Design Study of 30 MeV Linac for a Compact THz Radiation Source	2643
	S. Jummunt, S. Chunjarean, N. Juntong, S. Klinkhieo SLRI, Nakhon Ratchasima, Thailand K. Manasatitpong Synchrotron Light Research Institute (SLRI), Muang District, Thailand
	Funding: This work is supported by Science, Research, and Innovation Fund (SRI Fund) A compact THz radiation source plays a possibility to achieve intense THz radiation at tunable frequencies between 0.5 and 5.0 THz, with a peak power of several MW and narrow-bandwidth. This source requires essentially the reliable high gradient s-band linear accelerator (linac) to provide an electron beam energy up to 30 MeV with high bunch charge. In order to obtain a high gradient linac mentioned, the cavity structure has been optimized and performed using the software CST. The preliminary design of linac and beam dynamics study are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT030
About •	Received ※ 14 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 16 June 2022
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THPOPT033	Performance Characterisation at Daresbury Laboratory of Cs-Te Photocathodes Grown at CERN	2653
	L.A.J. Soomary, C.P. Welsch The University of Liverpool, Liverpool, United Kingdom C. Benjamin, H.M. Churn, L.B. Jones, T.C.Q. Noakes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C. Benjamin University of Warwick, Coventry, United Kingdom E. Chevallay, V.N. Fedosseev, E. Granados, M. Himmerlich, H. Panuganti CERN, Meyrin, Switzerland L.B. Jones, T.C.Q. Noakes, C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Funding: STFC Doctoral Training Studentship The search for high-performance photocathodes is a priority in the field of particle accelerators. The surface characteristics of a photocathode affect many important factors of the photoemission process including the photoemission threshold, the intrinsic emittance and the quantum efficiency. These factors in turn define the electron beam quality, which is measurable using figures of merit like beam emittance, brightness and energy spread. We present characterisation measurements for four caesium telluride photocathodes synthesized at CERN. The photocathodes were transported under ultra-high vacuum (UHV) and analysed at STFC Daresbury Laboratory, using ASTeC’s Multiprobe (SAPI)* for surface characterisation via XPS and STM, and for Mean Transverse Energy (MTE) measurements using the Transverse Energy Spread Spectrometer (TESS)*. The MTE measurements were estimated at cryogenic and room temperatures based on the respective transverse energy distribution curves. We discuss correlations found between the synthesis parameters, and the measured surface characteristics and MTE values. B.L. Militsyn, 4-th EuCARD2 WP12.5 meeting, Warsaw, 14-15 March 2017 **L.B. Jones et al., Proc. FEL ’13, TUPPS033, 290-293; https://accelconf.web.cern.ch/FEL2013/papers/tupso33.pdf
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT033
About •	Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 05 July 2022
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THPOPT034	Controlled Degradation of a Ag Photocathode by Exposure to Multiple Gases	2657
	L.A.J. Soomary, C.P. Welsch The University of Liverpool, Liverpool, United Kingdom L.B. Jones, T.C.Q. Noakes, C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom L.B. Jones, T.C.Q. Noakes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: STFC Doctoral Training Studentship The search for high performance photocathode electron sources is a priority in the accelerator science community. The surface characteristics of a photocathode define many important factors of the photoemission process including the work function, the intrinsic emittance and the quantum efficiency of the photocathode. These factors in turn define the ultimate electron beam quality, which is measurable as normalised emittance, brightness and energy spread. Strategies for improving these parameters vary, but understanding and influencing the relevant cathode surface physics which underpin these attributes is a primary focus for the community. We present performance data under illumination at 266 nm for Ag (100) single-crystal cathode and a Ag polycrystalline cathode after progressive exposure to O₂, CO₂, CO and N₂ using our TESS* instrument both at room and cryogenic temperatures. Crucially the data shows the effect of progressive degradation*** in the photocathode performance as a consequence of exposure to controlled levels of O₂ and that exposing an oxidized Ag surface to CO can drive partial QE recovery. K.L. Jensen; Appl. Phys. Lett. 89, 224103 (2006); L.B. Jones et al.; Proc. FEL ’13, TUPPS033, 290-293; **N. Chanlek et al.; J. Phys. D: Appl. Phys. (2014) 47, 055110;
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT034
About •	Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 10 July 2022
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THPOPT036	New Microwave Thermionic Electron Gun for APS Upgrade: Test Results and Operation Experience	2665
	S.V. Kutsaev, R.B. Agustsson, A.C. Araujo Martinez, R.D. Berry, O. Chimalpopoca, A.Y. Murokh, M. Ruelas, A.Yu. Smirnov, S.U. Thielk RadiaBeam, Santa Monica, California, USA J.E. Hoyt, W.G. Jansma, A. Nassiri, Y. Sun, G.J. Waldschmidt ANL, Lemont, Illinois, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Science, under contracts DE-SC0015191 and DE- AC02-06CH11357 Recently, RadiaBeam has designed and built a robust thermionic RF gun with optimized electromagnetic per-formance, improved thermal engineering, and a robust cathode mounting technique. This gun allows to improve the performance of existing and future light sources, industrial accelerators, and electron beam driven te-rahertz sources. Unlike conventional electrically or side-coupled RF guns, this new gun operates in ’-mode with the help of magnetic coupling holes. Such a design al-lows operation at longer pulses and has negligible dipole and quadrupole components. The gun prototype was built, then installed and tested at the Advanced Photon Source (APS) injector. This paper presents the results of high power and beam tests of this RF gun, and operation-al experience at APS to this moment.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT036
About •	Received ※ 31 May 2022 — Revised ※ 10 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 27 June 2022
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THPOPT044	The Alkali-Metal Photocathode Preparation Facility at Daresbury Laboratory: First Caesium Telluride Deposition Results	2693
	H.M. Churn, C. Benjamin, L.B. Jones, T.C.Q. Noakes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom C. Benjamin University of Warwick, Coventry, United Kingdom H.M. Churn, L.B. Jones, T.C.Q. Noakes Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Fourth generation light sources require high brightness electron beams. To achieve this a photocathode with a high quantum efficiency and low intrinsic emittance is required, which is also robust with a long operational lifetime and low dark current. Alkali-metal photocathodes have the potential to fulfil these requirements, so are an important research area for the accelerator physics community. STFC Daresbury Laboratory are currently commissioning the Alkali-metal Photocathode Preparation Facility (APPF) which will be used to grow alkali photocathodes. Photocathodes produced by the APPF will be analysed using Daresbury Laboratory’s existing Multiprobe system* and the Transverse Energy Spread Spectrometer (TESS). Multiprobe can perform a variety of surface analysis techniques while the TESS can measure the Mean Transverse Energy of a photocathode from its Transverse Energy Distribution Curve over a large range of illumination wavelengths. We present an overview on our current progress in the commissioning and testing of the APPF, the results from the first Cs-Te deposition and detail the work planned to facilitate the manufacture of Cs₂Te photocathodes for the CLARA accelerator. B.L. Militsyn, 4th EuCARD2 WP12.5 meeting, Warsaw, 14-15 Mar. 2017 L. Jones et al., Proc. FEL ’13, TUPPS033, 290-293 *D. Angal-Kalinin et al., Phys. Rev. Accel. Beams, Vol. 23, Iss. 4, 2020
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT044
About •	Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 23 June 2022
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THPOTK014	100 keV Electron Source Design for the New 3 GeV Synchrotron Facility in Thailand	2800
	N. Juntong, S. Bootiew, T. Chanwattana, Ch. Dhammatong, S. Jummunt, K. Kittimanapun, W. Phacheerak SLRI, Nakhon Ratchasima, Thailand K. Manasatitpong Synchrotron Light Research Institute (SLRI), Muang District, Thailand
	The Synchrotron Light Research Institute (SLRI) is developing a new synchrotron light source with an electron beam energy of 3 GeV. The DC thermionic electron gun was chosen because it is simple and less cost. The design process is well known. The operation is more stable compared to the RF gun. The cathode Y-646B was considered because it had already been used at the old synchrotron machine and the possibility of sharing the stock outweighs other disadvantages. Moreover, it is used in many synchrotron facilities, so it is easy to find references. The present of the focusing electrode was discussed. The focusing electrode will increase the complexity of the gun, but it is necessary to get a high-quality beam from the gun. The designed electron gun can produce 1.1 A beams current with the normalized emittance of 0.910 Pi·mm·mrad, which satisfied the requirement of the linac injector. The design and study results will be discussed in this report.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOTK014
About •	Received ※ 20 May 2022 — Accepted ※ 14 June 2022 — Issue date ※ 29 June 2022
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Paper

Title

Page

THPOST046

CrYogenic Brightness-Optimized Radiofrequency Gun (CYBORG)

2544

SUSPMF021

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

G.E. Lawler, A. Fukasawa, N. Majernik, J.R. Parsons, J.B. Rosenzweig, Y. Sakai, A. Suraj
UCLA, Los Angeles, California, USA

Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE Contract DE-SC0020409
Producing higher brightness beams at the cathode is one of the main focuses for future electron beam applications. For photocathodes operating close to their emission threshold, the cathode lattice temperature begins to dominate the minimum achievable intrinsic emittance. At UCLA, we are designing a radiofrequency (RF) test bed for measuring the temperature dependence of the mean transverse energy (MTE) and quantum efficiency for a number of candidate cathode materials. We intend to quantify the attainable brightness improvements at the cathode from cryogenic operation and establish a proof-of-principle cryogenic RF gun for future studies of a 1.6-cell cryogenic photoinjector for the UCLA ultra compact XFEL concept (UC-XFEL). The test bed will use a C-band 0.5-cell RF gun designed to operate down to 45 K, producing an on-axis accelerating field of 120 MV/m. The cryogenic system uses conduction cooling and a load-lock system is being designed for transport and storage of air-sensitive high brightness cathodes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOST046

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Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 01 July 2022

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THPOPT005

Field Enhanced, Compact S-Band Gun Employing a Pin Cathode

2567

SUSPMF020

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

R. Bazrafshan, T. Rohwer
Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
M. Fakhari, K. Flöttmann, F.X. Kaernter
DESY, Hamburg, Germany
N.H. Matlis
CFEL, Hamburg, Germany

S-band RF-guns are highly developed for production of low emittance relativistic electron bunches, but need powerful klystrons for driving. Here, we present the design and first experimental tests of a compact S-band gun, which can accelerate electrons up to 180 keV powered by only 10 kW from a compact rack-mountable solid-state amplifier. A pin-cathode is used to enhance the RF electric field on the cathode up to 100 MV/m as in large-scale S-band guns. An electron bunch is generated through photoemission off a flat copper surface on the pin excited by a UV laser pulse followed by a focusing solenoid producing a low emittance bunch with 0.1 mm mrad transverse emittance for up to 100 fC bunch charge. We are currently in the conditioning phase of the gun and first experiments show good agreement with simulations. The compact gun will serve three purposes: (i) it can be used directly for ultrafast electron diffraction; (ii) as an injector into a THz booster producing 0.3MeV to 2 MeV electron bunches for ultrafast electron diffraction; (iii) The system in (ii) serves as an injector into a THz linear accelerator producing a 20 MeV beam for the AXSIS X-ray source project.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT005

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Received ※ 21 May 2022 — Revised ※ 12 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 10 July 2022

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THPOPT019

Multi-Alkali Antimonide Photocathode Development for High Brightness Beams

2610

S. Mistry, T. Kamps, J. Kühn, C. Wang
HZB, Berlin, Germany
T. Kamps
HU Berlin, Berlin, Germany
C. Wang
University Siegen, Siegen, Germany

Funding: This work is funded by the DFG CO 1509/10-1 | MI 2917/1-1
Photocathode R&D at the Helmholtz-Zentrum Berlin (HZB) is driven by the motivation to produce high brightness electron beams for the SRF photoinjector test facility, Sealab/ bERLinPro. Multi-alkali antimonides are the choice photocathode material due to high quantum efficiency (QE) and low intrinsic emittance in the visible range. In this work a more robust alternative to the tried and tested Cs-K-Sb is considered. Na-K-Sb offers similar advantages to Cs-K-Sb including, high QE at green wavelengths but moreover, it offers excellent stability at elevated temperatures. This property could lengthen the cathode lifetime by enhancing the robustness of the photocathode inside the SRF gun. In this work, a status report showcasing first results towards the development of a growth procedure for Na-K-Sb is presented by means of spectral response and XPS measurements conducted in the HZB photocathode lab.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT019

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Received ※ 03 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 04 July 2022

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THPOPT020

Status and Plans for the New CLS Electron Source Lab

2614

M.J. Boland, D. Bertwistle, F. Le Pimpec
CLS, Saskatoon, Saskatchewan, Canada
X.F.D. Stragier
TUE, Eindhoven, The Netherlands

The Canadian Light Source (CLS) has recently created a new Electron Source Lab (ESL) that can run independently from user operations. A section of the old Saskatchewan Accelerator Laboratory experimental nuclear physics tunnels has been rebuilt with new shielding and a separate entrance. The laboratory will be used to prepare an operational spare electron gun for the 250 MeV linac. In addition, there are plans to develop RF guns for a future branch line to inject into the linac and for possible short pulse production. This paper will give an overview of the ESL space and the first electron guns which plan to be installed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT020

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Received ※ 16 June 2022 — Revised ※ 29 June 2022 — Accepted ※ 04 July 2022 — Issue date ※ 08 July 2022

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THPOPT022

Study on QE Evolution of Cs₂Te Photocathodes in ELBE SRF Gun-II

2617

R. Xiang, A. Arnold, S. Ma, P. Michel, P. Murcek, A.A. Ryzhov, J. Schaber, J. Teichert, P.Z. Zwartek
HZDR, Dresden, Germany

The quality of the photocathodes is critical for the sta-bility and reliability of the photoinjector’s operation. Thanks to the robust magnesium and Cs₂Te photocathodes, SRF gun-II at HZDR has been proven to be a suc-cessful example in CW mode for high current user operation. In this contribution, we will present our observation of the QE evolution of Cs₂Te photocathodes during SRF gun operation. The variables including substrate surface, film thickness, Cs/Te stoichiometric, multipacting, RF loading and charge extract are considered in the analysis.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT022

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Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 06 July 2022

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THPOPT024

MIST - The MESA-Injector Source Two

2624

M.A. Dehn, P.S. Plattner
IKP, Mainz, Germany
K. Aulenbacher
HIM, Mainz, Germany
K. Aulenbacher
GSI, Darmstadt, Germany
K. Aulenbacher
KPH, Mainz, Germany

Funding: Work supported by the German science ministry BMBF through Verbundforschung
The new accelerator MESA (Mainz Energy Recovering Superconducting Accelerator) will provide an average CW electron beam current of up to 10 mA. Operating at 1.3 GHz, this corresponds to a bunch charge of 7.7 pC. The new DC photoemission source MIST is optimized for these requirements. A challenge is heating of the photocathode at high laser power. By a suitable mechanical construction and the use of specific materials, the heat can be dissipated during operation. Options for further improvements are discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT024

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Received ※ 07 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 01 July 2022

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THPOPT025

Photocathode Stress Test Bench at INFN LASA

2627

D. Sertore, D. Giove, L. Monaco
INFN/LASA, Segrate (MI), Italy
A. Bacci, F. Canella, S. Cialdi, I. Drebot, D. Giannotti, L. Serafini
INFN-Milano, Milano, Italy
D. Cipriani, E. Suerra
Università degli Studi di Milano, Milano, Italy
G. Galzerano
POLIMI, Milano, Italy
G. Guerini Rocco
Università degli Studi di Milano & INFN, Segrate, Italy

A UHV test bench based on a 100 kV DC gun and a 100 MHz repetition rate laser has been setup up at INFN LASA to test Cs₂Te photocathodes. This operation mode is the baseline of the BriXSinO project, currently in the design phase in our laboratory, and the qualification of the Cs₂Te photocathodes is a key issue. In this paper, we present the recent advances in the different aspects of this R&D activity.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT025

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Received ※ 10 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 20 June 2022

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THPOPT026

Assembly and Characterization of Low-Energy Electron Transverse Momentum Measurement Device (TRAMM) at INFN LASA

2630

D. Sertore, M. Bertucci, A. Bosotti, D. Giove, L. Monaco, R. Paparella
INFN/LASA, Segrate (MI), Italy
G. Guerini Rocco, C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

In the framework of high-brightness electron beam generation, thermal emittance is nowadays a key parameter. While alkali tellurides are extensively used in advanced electron sources, alkali antimonides photocathodes demonstrated high QE in the visible, thus making feasible CW operations for RF-based photoinjectors. The INFN LASA laboratory in Milan is fully equipped with dedicated production systems for photocathode preparation and optical setup for QE evaluation. In this paper, we describe a newly designed device dedicated to electron transverse momentum measurement (TRAMM). It will be connected to the main production chambers and will serve as an "emittance monitoring" system during photocathode growth. From the design phase, through the parameter estimate, assembly of the components, to the installation and first measurements, we describe the status of this project and its future developments.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT026

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Received ※ 09 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 07 July 2022

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THPOPT027

R&D on High QE Photocathodes at INFN LASA

2633

D. Sertore, M. Bertucci, L. Monaco
INFN/LASA, Segrate (MI), Italy
G. Guerini Rocco
Università degli Studi di Milano & INFN, Segrate, Italy
S.K. Mohanty, H.J. Qian, F. Stephan
DESY Zeuthen, Zeuthen, Germany

We present the recent activities on antimonide and telluride alkali based photocathodes at INFN LASA. The R&D on Cs₂Te materials is focused on investigating effects of material thickness and growth procedures on the photocathodes performances during operation in RF guns. We aim to improve thermal emittance and long term stability of these films. The more recent work on alkali antimonide showed the need for substantial improvements in stability and QE during operation. We present here our recent achievements and plans for future activities.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT027

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Received ※ 09 June 2022 — Revised ※ 16 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022

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THPOPT028

Dependence of CsK2Sb Photocathode Performance on the Quality of Graphene Substrate Film

2637

L. Guo, K. Goto, Y. Takashima
Nagoya University, Nagoya, Japan
H. Yamaguchi
LANL, Los Alamos, New Mexico, USA
M. Yamamoto
KEK, Ibaraki, Japan

Funding: U.S.-Japan Science and Technology Cooperation Program in High Energy Physics
A photocathode that extracts electrons by irradiating a semiconductor or metal with a laser is applied to advanced accelerators and electron microscopes as a high-performance cathode. In particular, the CsK2Sb photocathode is of interest because it has features such as low emittance, excitability with visible light, and high quantum efficiency. Generally, the CsK2Sb photocathode is produced by depositing a cathode element on a substrate, so that the cathode performance strongly depends on the surface condition of the substrate. We have found graphene as reusable substrate, which has the property of being chemically inactive. In this study, graphene film quality dependence of CsK2Sb photo-cathode performance was evaluated. Specifically, CsK2Sb cathode was deposited using different quality graphene film substrates and their QE values and uniformity were compared. The quality of graphene films was analyzed using X-ray Photoelectron Spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). We found that the graphene film can be cleaned by heating at 500 deg. The QE of the cathode on a good quality graphene film was higher and more uniform than that on a poor quality graphene film.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT028

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Received ※ 16 May 2022 — Revised ※ 10 June 2022 — Accepted ※ 10 June 2022 — Issue date ※ 24 June 2022

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THPOPT029

Study on the Performance Improvement of Alkali Antimonide Photocathodes for Radio Frequency Electron Guns

2640

R. Fukuoka, K. Ezawa, Y. Koshiba, M. Washio
Waseda University, Tokyo, Japan
K. Sakaue
The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan

Semiconductor photocathodes such as Cs-Te and Cs-K-Sb are used as electron sources in accelerators to generate high brightness beams using radio frequency (rf) electron guns. Alkali antimonide photocathodes have a high quantum efficiency (Q.E.) of ~10%, and their excitation wavelength is in the visible light region (532 nm), so that they are expected to reduce the requirements on the optical system and increase the amount of charge compared to Cs-Te. However, alkali antimonide photocathodes have a short lifetime and degrade under poor vacuum conditions, so it is essential to improve durability by protective film coatings. Therefore, we are currently working on the fabrication of high Q.E. alkali antimonide photocathodes that can withstand the Q.E. reduction during coating. In this presentation, we will report the results of comparison between the fabricated alkali antimonide photocathode and Cs-Te photocathode, and future prospects.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT029

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Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 09 July 2022

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THPOPT030

Design Study of 30 MeV Linac for a Compact THz Radiation Source

2643

S. Jummunt, S. Chunjarean, N. Juntong, S. Klinkhieo
SLRI, Nakhon Ratchasima, Thailand
K. Manasatitpong
Synchrotron Light Research Institute (SLRI), Muang District, Thailand

Funding: This work is supported by Science, Research, and Innovation Fund (SRI Fund)
A compact THz radiation source plays a possibility to achieve intense THz radiation at tunable frequencies between 0.5 and 5.0 THz, with a peak power of several MW and narrow-bandwidth. This source requires essentially the reliable high gradient s-band linear accelerator (linac) to provide an electron beam energy up to 30 MeV with high bunch charge. In order to obtain a high gradient linac mentioned, the cavity structure has been optimized and performed using the software CST. The preliminary design of linac and beam dynamics study are presented in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT030

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Received ※ 14 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 16 June 2022

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THPOPT033

Performance Characterisation at Daresbury Laboratory of Cs-Te Photocathodes Grown at CERN

2653

L.A.J. Soomary, C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
C. Benjamin, H.M. Churn, L.B. Jones, T.C.Q. Noakes
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
C. Benjamin
University of Warwick, Coventry, United Kingdom
E. Chevallay, V.N. Fedosseev, E. Granados, M. Himmerlich, H. Panuganti
CERN, Meyrin, Switzerland
L.B. Jones, T.C.Q. Noakes, C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Funding: STFC Doctoral Training Studentship
The search for high-performance photocathodes is a priority in the field of particle accelerators. The surface characteristics of a photocathode affect many important factors of the photoemission process including the photoemission threshold, the intrinsic emittance and the quantum efficiency. These factors in turn define the electron beam quality, which is measurable using figures of merit like beam emittance, brightness and energy spread. We present characterisation measurements for four caesium telluride photocathodes synthesized at CERN. The photocathodes were transported under ultra-high vacuum (UHV) and analysed at STFC Daresbury Laboratory, using ASTeC’s Multiprobe (SAPI)* for surface characterisation via XPS and STM, and for Mean Transverse Energy (MTE) measurements using the Transverse Energy Spread Spectrometer (TESS)**. The MTE measurements were estimated at cryogenic and room temperatures based on the respective transverse energy distribution curves. We discuss correlations found between the synthesis parameters, and the measured surface characteristics and MTE values.
*B.L. Militsyn, 4-th EuCARD2 WP12.5 meeting, Warsaw, 14-15 March 2017
**L.B. Jones et al., Proc. FEL ’13, TUPPS033, 290-293; https://accelconf.web.cern.ch/FEL2013/papers/tupso33.pdf

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT033

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Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 05 July 2022

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THPOPT034

Controlled Degradation of a Ag Photocathode by Exposure to Multiple Gases

2657

L.A.J. Soomary, C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
L.B. Jones, T.C.Q. Noakes, C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom
L.B. Jones, T.C.Q. Noakes
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Funding: STFC Doctoral Training Studentship
The search for high performance photocathode electron sources is a priority in the accelerator science community. The surface characteristics of a photocathode define many important factors of the photoemission process including the work function, the intrinsic emittance and the quantum efficiency of the photocathode. These factors in turn define the ultimate electron beam quality, which is measurable as normalised emittance, brightness and energy spread. Strategies for improving these parameters vary, but understanding and influencing the relevant cathode surface physics which underpin these attributes is a primary focus for the community*. We present performance data under illumination at 266 nm for Ag (100) single-crystal cathode and a Ag polycrystalline cathode after progressive exposure to O₂, CO₂, CO and N₂ using our TESS** instrument both at room and cryogenic temperatures. Crucially the data shows the effect of progressive degradation*** in the photocathode performance as a consequence of exposure to controlled levels of O₂ and that exposing an oxidized Ag surface to CO can drive partial QE recovery.
*K.L. Jensen; Appl. Phys. Lett. 89, 224103 (2006);
**L.B. Jones et al.; Proc. FEL ’13, TUPPS033, 290-293;
***N. Chanlek et al.; J. Phys. D: Appl. Phys. (2014) 47, 055110;

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT034

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Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 10 July 2022

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THPOPT036

New Microwave Thermionic Electron Gun for APS Upgrade: Test Results and Operation Experience

2665

S.V. Kutsaev, R.B. Agustsson, A.C. Araujo Martinez, R.D. Berry, O. Chimalpopoca, A.Y. Murokh, M. Ruelas, A.Yu. Smirnov, S.U. Thielk
RadiaBeam, Santa Monica, California, USA
J.E. Hoyt, W.G. Jansma, A. Nassiri, Y. Sun, G.J. Waldschmidt
ANL, Lemont, Illinois, USA

Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Science, under contracts DE-SC0015191 and DE- AC02-06CH11357
Recently, RadiaBeam has designed and built a robust thermionic RF gun with optimized electromagnetic per-formance, improved thermal engineering, and a robust cathode mounting technique. This gun allows to improve the performance of existing and future light sources, industrial accelerators, and electron beam driven te-rahertz sources. Unlike conventional electrically or side-coupled RF guns, this new gun operates in ’-mode with the help of magnetic coupling holes. Such a design al-lows operation at longer pulses and has negligible dipole and quadrupole components. The gun prototype was built, then installed and tested at the Advanced Photon Source (APS) injector. This paper presents the results of high power and beam tests of this RF gun, and operation-al experience at APS to this moment.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT036

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Received ※ 31 May 2022 — Revised ※ 10 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 27 June 2022

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THPOPT044

The Alkali-Metal Photocathode Preparation Facility at Daresbury Laboratory: First Caesium Telluride Deposition Results

2693

H.M. Churn, C. Benjamin, L.B. Jones, T.C.Q. Noakes
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
C. Benjamin
University of Warwick, Coventry, United Kingdom
H.M. Churn, L.B. Jones, T.C.Q. Noakes
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Fourth generation light sources require high brightness electron beams. To achieve this a photocathode with a high quantum efficiency and low intrinsic emittance is required, which is also robust with a long operational lifetime and low dark current. Alkali-metal photocathodes have the potential to fulfil these requirements, so are an important research area for the accelerator physics community. STFC Daresbury Laboratory are currently commissioning the Alkali-metal Photocathode Preparation Facility (APPF) which will be used to grow alkali photocathodes. Photocathodes produced by the APPF will be analysed using Daresbury Laboratory’s existing Multiprobe system* and the Transverse Energy Spread Spectrometer (TESS)**. Multiprobe can perform a variety of surface analysis techniques while the TESS can measure the Mean Transverse Energy of a photocathode from its Transverse Energy Distribution Curve over a large range of illumination wavelengths. We present an overview on our current progress in the commissioning and testing of the APPF, the results from the first Cs-Te deposition and detail the work planned to facilitate the manufacture of Cs₂Te photocathodes for the CLARA accelerator***.
*B.L. Militsyn, 4th EuCARD2 WP12.5 meeting, Warsaw, 14-15 Mar. 2017
**L. Jones et al., Proc. FEL ’13, TUPPS033, 290-293
***D. Angal-Kalinin et al., Phys. Rev. Accel. Beams, Vol. 23, Iss. 4, 2020

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOPT044

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Received ※ 07 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 23 June 2022

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THPOTK014

100 keV Electron Source Design for the New 3 GeV Synchrotron Facility in Thailand

2800

N. Juntong, S. Bootiew, T. Chanwattana, Ch. Dhammatong, S. Jummunt, K. Kittimanapun, W. Phacheerak
SLRI, Nakhon Ratchasima, Thailand
K. Manasatitpong
Synchrotron Light Research Institute (SLRI), Muang District, Thailand

The Synchrotron Light Research Institute (SLRI) is developing a new synchrotron light source with an electron beam energy of 3 GeV. The DC thermionic electron gun was chosen because it is simple and less cost. The design process is well known. The operation is more stable compared to the RF gun. The cathode Y-646B was considered because it had already been used at the old synchrotron machine and the possibility of sharing the stock outweighs other disadvantages. Moreover, it is used in many synchrotron facilities, so it is easy to find references. The present of the focusing electrode was discussed. The focusing electrode will increase the complexity of the gun, but it is necessary to get a high-quality beam from the gun. The designed electron gun can produce 1.1 A beams current with the normalized emittance of 0.910 Pi·mm·mrad, which satisfied the requirement of the linac injector. The design and study results will be discussed in this report.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOTK014

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Received ※ 20 May 2022 — Accepted ※ 14 June 2022 — Issue date ※ 29 June 2022

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