IPAC2021 - List of Keywords (cathode)

Paper	Title	Other Keywords	Page
MOXC02	Improved Lifetime of a High Spin Polarization Superlattice Photocathode	electron, polarization, gun, vacuum	31
	L. Cultrera BNL, Upton, New York, USA
	Funding: Department of Energy under grant DE-SC0012704 Highly spin polarized electron beams are required for the operation of a wide range of accelerators and instruments. The production of such electrons requires the use of Negative Electron Affinity (NEA) activated GaAs-based cathodes operated in photoelectron guns. Because of their extreme sensitivity to poor vacuum conditions the degradation of the photoemission process is so strong that NEA activated GaAs-based photocathodes can only survive in the extreme vacuums typical of DC gun. State-of-the-art on photocathode technology for spin polarized beam productions are summarized. Recent results on the use of robust NEA coating based on the Cs-Te and Cs-Sb leading to improved operational lifetime of a high spin polarization photocathode are reviewed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOXC02
About •	paper received ※ 20 May 2021 paper accepted ※ 19 July 2021 issue date ※ 11 August 2021
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MOPAB138	Dielectric Wakefield Acceleration with a Laser Injected Witness Beam	wakefield, laser, experiment, simulation	481
	G. Andonian, T.J. Campese RadiaBeam, Santa Monica, California, USA N.M. Cook RadiaSoft LLC, Boulder, Colorado, USA D.S. Doran, G. Ha, J.G. Power, J.H. Shao, E.E. Wisniewski ANL, Lemont, Illinois, USA W.J. Lynn, N. Majernik, J.B. Rosenzweig, V.S. Yu UCLA, Los Angeles, California, USA
	Funding: Work supported by DOE grant DE-SC0017690 The plasma photocathode concept, whereby a two-species gas mixture is used to generate a beam -driven accelerating wakefield and a laser-ionized generation of a witness beam, was recently experimentally demonstrated. In a variation of this concept, a beam-driven dielectric wakefield accelerator is employed, filled with a neutral gas for laser-ionization and creation of a witness beam. The dielectric wakefields, in the terahertz regime, provide comparatively modest timing requirements for the injection phase of the witness beam. In this paper, we provide an update on the progress of the experimental realization of the hybrid dielectric wakefield accelerator with laser injected witness beam at the Argonne Wakefield Accelerator (AWA), including engineering considerations for gas delivery, and preliminary simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB138
About •	paper received ※ 19 May 2021 paper accepted ※ 17 June 2021 issue date ※ 15 August 2021
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MOPAB153	Laser Microfabrication for Accelerator Applications	laser, FEM, simulation, emittance	535
	S.P. Antipov, S.V. Kuzikov Euclid TechLabs, Solon, Ohio, USA A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia
	Laser microfabrication allows high precision ablation of materials at sub-mm scale. When laser pulse length is shorter than about 10 picoseconds the heat affected zone is minimized and ablation occurs without melting. Work-pieces processed in this fashion exhibit less structural damage and are expected to have a higher damage thresholds. In this paper we will review several case studies of laser-microfabricated components for accelerator and x-ray applications. Ablated materials include diamond, quartz, tungsten, copper, YAG:Ce and silicon.
	Poster MOPAB153 [2.781 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB153
About •	paper received ※ 20 May 2021 paper accepted ※ 01 July 2021 issue date ※ 31 August 2021
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MOPAB257	Effects of Mode Launcher on Beam Dynamics in Next Generation High Brightness C-Band Guns	gun, emittance, simulation, electron	813
	A. Giribono, D. Alesini, F. Cardelli, G. Di Raddo, M. Ferrario, A. Gallo, J. Scifo, C. Vaccarezza, A. Vannozzi INFN/LNF, Frascati (Roma), Italy G. Castorina AVO-ADAM, Meyrin, Switzerland L. Ficcadenti INFN-Roma, Roma, Italy G. Muti Sapienza University of Rome, Rome, Italy G. Pedrocchi SBAI, Roma, Italy
	High-brightness RF photo-injectors plays nowadays a crucial role in the fields of radiation generation and advanced acceleration schemes. A high gradient C-band photoinjector consisting of a 2.5 cell gun followed by TW sections is here proposed as an electron source for radiation user facilities. The paper reports on beam dynamics studies in the RF injector and illustrates the effects on the beam quality of the mode launcher with a focus on the compensation of the quadrupole RF components.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB257
About •	paper received ※ 19 May 2021 paper accepted ※ 08 June 2021 issue date ※ 12 August 2021
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TUPAB033	Photocathode Stress Test Bench at INFN LASA	laser, gun, electron, high-voltage	1413
	D. Sertore, D. Giove, G. Guerini Rocco, 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
	In the framework of the preparatory activities to the BriXSino project, a test bench for testing Cs₂Te photocathode at 100 MHz laser repetition rate has been installed at INFN LASA. This high repetition operation mode is foreseen to be the base operation mode of BriXSino and a qualification of the Cs₂Te photocathodes is a key component. While we are not at full specification due to the limited HV of the present DC gun, we discuss the status of the test bench and the initial results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB033
About •	paper received ※ 19 May 2021 paper accepted ※ 27 May 2021 issue date ※ 16 August 2021
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TUPAB034	Development of Multi-Alkali Antimonides Photocathodes for High-Brightness RF Photoinjectors	electron, emittance, site, laser	1416
	S.K. Mohanty, M. Krasilnikov, A. Oppelt, H.J. Qian, F. Stephan DESY Zeuthen, Zeuthen, Germany G. Guerini Rocco, C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany P. Michelato, L. Monaco, D. Sertore INFN/LASA, Segrate (MI), Italy
	Multi-alkali antimonide-based photocathodes are suitable candidate for the electron sources of next-generation high brightness RF photoinjectors due to their excellent photoemissive properties especially, like low thermal emittances and high sensitivity to visible light. The former stands out, paving the way towards CW operations. Based on the previous successful development of Cesium Telluride photocathodes, we are now channelling our efforts toward an R&D activity focused on KCsSb and NaKSb(Cs) photocathodes. Parallel to that R&D activity, we have installed a new dedicated photocathode production system at the INFN-LASA to start the preparation of these photocathodes for their test in the PITZ photoinjector at DESY in Zeuthen. In this paper, detailed experimental results obtained from the KCsSb, along with a preliminary result from the NaKSb(Cs) photocathode material as well as the status of the overall project are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB034
About •	paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 02 September 2021
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TUPAB037	The Design of a High Charge Polarized Preinjector for the Electron-Ion Collider	gun, cavity, linac, electron	1428
	E. Wang, W. Liu, V.H. Ranjbar, J. Skaritka, N. Tsoupas BNL, Upton, New York, USA J.M. Grames, J. Guo JLab, Newport News, Virginia, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy The design of the electron pre-injector of the Electron-Ion Collider (EIC) project to generate 4 x 7 nC bunch has been advancing to meet the requirements for injection into the Rapid Cycling Synchrotron (RCS). The major challenges are high charge transport and achieving small energy spread from 3 GHz traveling-wave plate(TWP). The designed preinjector includes the polarized electron source, bunching section, TWP Linac, zigzag phase space manipulation and spin rotator. In this report, we will discuss the RF frequency selection and the way to reduce energy spread down to 0.2% by longitudinal phase space manipulate. We will also report the results of beamline simulation using space charge code and the conceptual design of spin rotator.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB037
About •	paper received ※ 16 May 2021 paper accepted ※ 15 June 2021 issue date ※ 31 August 2021
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TUPAB105	Simulation Studies for Dark Current Signature From DLS RF Gun	simulation, electron, cavity, solenoid	1630
	J. Karmakar, M. Aggarwal, S. Ghosh, B. Karmakar, P. Patra, B.K. Sahu, A. Sharma IUAC, New Delhi, India
	The Delhi Light source (DLS) is an upcoming compact THz facility at IUAC, New Delhi, based on pre-bunched FEL. RF conditioning of the 2.6 cell S-band RF gun is presently carried out with a Cu photo-cathode (PC) plug and dark current is produced when substantial accelerating field is reached inside the cavity. To identify the possible field emission sites contributing to dark current, single electron ASTRA simulations are done with a phase scan of the RF field. The simulation is extended to include multi-particle emission from the PC edge as a ring. The energies present in the dark current is analysed from the the Fowler Nordheim current plot and energy phase scan plot. The distribution of few dark current energies and their respective trajectories upto the YAG screen at a given solenoid setting is traced and shown in the simulations. We also present the dark current images captured during the initial RF conditioning and try to compare it with the simulations.
	Poster TUPAB105 [0.742 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB105
About •	paper received ※ 19 May 2021 paper accepted ※ 17 August 2021 issue date ※ 28 August 2021
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TUPAB121	Photoinjector Drive Laser Temporal Shaping for Shanghai Soft X-Ray Free Electron Laser	laser, electron, FEL, flattop	1674
	C.L. Li, X.T. Wang, W.Y. Zhang Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China X.L. Dai SSRF, Shanghai, People’s Republic of China H.X. Deng, L. Feng, B. Liu, J.G. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China
	Shanghai soft X ray free electron laser (SXFEL) initial designed shape of the photocathode driver laser is flattop produced by α-BBO stacking. The advantage of this design is attractive in producing electron bunch with low initial emittance and high uniformity along the electron bunch. However, some unavoidable modulations are generated along the laser pulse which trigger the electron bunch modulation generated at the source, which is due to the fast response time (tens of femtosecond) of copper cathode. In order to eliminate the modulation of electron bunch, temporal Gaussian driver laser was designed and tested, measurement results show the electron bunch longitudinal modulation was removed. In this paper, we present two kinds of driver laser pulse temporal shaping methods based on α-BBO stacking and UV grating pair shaping. Moreover, corresponding electron bunch temporal profile are also presented.
	Poster TUPAB121 [2.469 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB121
About •	paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 10 August 2021
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TUPAB127	Spare Gun Multi-Physics Analysis for LCLS-II	gun, cavity, simulation, electron	1688
	L. Xiao, C. Adolphsen, A. Cedillo, E.N. Jongewaard, X. Liu, C.-K. Ng, F. Zhou SLAC, Menlo Park, California, USA
	LBNL APEX VHF normal conducting gun was adopted for LCLS-II CW operation to provide ultra-bright high repetition rate X-ray pulses. The initial LCLS-II gun and injector commissioning showed excessive dark current dominated by field emission around the cathode plug outer diameter and the gun cavity nose. There is a concern that the dark current may get worse with time of operation. It is planning to build a spare rf gun largely based on the current LCLS-II gun to replace current LCLS-II gun. The proposed spare gun has a reduced the peak electrical fields around the cathode plug corner and cavity nose by 10% through further optimizing APEX gun cavity shape. In addition, there are some moderate modifications on the engineering design to increase mechanical robustness and vacuum performance. SLAC developed parallel finite-element electromagnetic code suite ACE3P is used to apply for the spare gun modeling including RF, thermal and structural analysis at static and transient states to ensure its successful operation in LCLS-II. In this paper, the spare gun multi-physics analysis is described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB127
About •	paper received ※ 19 May 2021 paper accepted ※ 20 August 2021 issue date ※ 25 August 2021
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TUPAB200	Status of the Electron Lens for Space Charge Compensation in SIS18	electron, gun, solenoid, space-charge	1880
	K. Schulte-Urlichs, S. Artikova, D. Ondreka, P.J. Spiller GSI, Darmstadt, Germany P. Apse-Apsitis, I. Steiks Riga Technical University, Riga, Latvia M. Droba, O. Meusel, H. Podlech, K.I. Thoma IAP, Frankfurt am Main, Germany
	At GSI a project has been initiated to investigate the option of space charge compensation (SCC) by use of an electron lens in order to overcome space charge (SC) limits in the synchrotrons SIS18 and SIS100 for the Facility for Antiproton and Ion Research (FAIR). The repeated crossing of resonance lines due to the synchrotron motion in bunched beams is considered one of the main drivers of SC induced beam loss in the synchrotrons. Electron lenses provide a compensation of ion beam SC by virtue of their negative charge interacting with the ions in the overlap region while a time-varying compensation can be achieved by the modulation of the electron beam. In order to demonstrate space charge compensation of bunched ion beams, an electron lens is under development for the application in SIS18. In this contribution, the status of the electron lens design will be reported putting special emphasis on its main components: the RF modulated electron gun, that is being developed within an ARIES collaboration, and the magnet system.
	Poster TUPAB200 [1.869 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB200
About •	paper received ※ 19 May 2021 paper accepted ※ 23 June 2021 issue date ※ 17 August 2021
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TUPAB236	Progress on the Electron Gun Design for a McMillan Electron Lens in the Fermilab Integrable Optics Test Accelerator (IOTA)	electron, gun, simulation, optics	1988
	B.L. Cathey, G. Stancari Fermilab, Batavia, Illinois, USA
	Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. This paper covers the progress made so far in designing the first McMillan electron lens for the Fermilab IOTA ring. The novel design allows for an increase in tune spread without limiting the dynamic aperture due to its integrability. Shown are simulations for an electron gun design to generate the specific required current density distribution for the nonlinear integrable system in IOTA.
	Poster TUPAB236 [5.391 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB236
About •	paper received ※ 19 May 2021 paper accepted ※ 19 July 2021 issue date ※ 25 August 2021
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TUPAB366	Design and Realization of New Solenoids for High Brightness Electron Beam Injectors	solenoid, gun, electron, simulation	2374
	A. Vannozzi, D. Alesini, A. Giribono, C. Vaccarezza INFN/LNF, Frascati (Roma), Italy
	High-brightness, high-current electron beams are the main requirement for fourth generation light sources such as free-electron lasers (FELs), energy recovery Linacs (ERLs) and high-energy linear colliders. The most successful device for producing such beams is the Radio-Frequency photoinjector where a key element is the gun solenoid. Its main task is to limit the beam emittance growth in the first acceleration stages by imposing a spiraling motion to the beam. This paper is focused on two magnets: the first one is the solenoid gun for the new photoinjector at INFN-LNF SPARC_LAB test facility. The design, the realization, and all the measurements performed at the factory and at LNF are shown. Moreover, the design of a solenoid for a novel C-band gun for CompactLight project is presented. Both magnets have been designed with the goal to reach the same integrated field of the gun solenoid currently installed at SPARC_LAB, with an integrated field quality of 5·10^-4 in a good field radius of 30mm and 10mm radius respectively for SPARC_LAB and CompactLight solenoid. This one is equipped with a bucking coil to limit the field on cathode that could led to an undesired emittance growth.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB366
About •	paper received ※ 19 May 2021 paper accepted ※ 18 June 2021 issue date ※ 12 August 2021
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TUPAB396	The Thermal Outgassing Rate of Materials Used in Vacuum Systems	vacuum, experiment, diagnostics, radiation	2447
	A.M. Semenov BINP & NSTU, Novosibirsk, Russia A. Burdakov, A.A. Krasnov, B.P. Tolochko, A.V. Varand BINP SB RAS, Novosibirsk, Russia S.R. Ivanova GPI, Moscow, Russia A.A. Krasnov NSU, Novosibirsk, Russia M.A. Mikhailenko ISSCM SB RAS, Novosibirsk, Russia A.A. Shoshin Budker INP & NSU, Novosibirsk, Russia
	There are many rarely used materials in vacuum systems that are poorly investigated in terms of vacuum properties. For example, phosphors, scintillating materials, ferrites, various adhesives, etc. In addition, new organic materials are being developed with mechanical properties similar to those of conventional steel. The use of such materials is very promising in vacuum technology. This article presents the thermal degassing performance of several rarely used materials and promising materials for vacuum applications.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB396
About •	paper received ※ 18 May 2021 paper accepted ※ 26 August 2021 issue date ※ 31 August 2021
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WEXA02	Operational Electron Cooling in the Relativistic Heavy Ion Collider	electron, operation, collider, cavity	2516
	A.V. Fedotov, K.A. Drees, W. Fischer, X. Gu, D. Kayran, J. Kewisch, C. Liu, K. Mernick, M.G. Minty, V. Schoefer, H. Zhao 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. Since the invention of the electron cooling technique its application to cool hadron beams in colliders was considered for numerous accelerator physics projects worldwide. However, achieving the required high-brightness electron beams of required quality and cooling of ion beams in collisions was deemed to be challenging. An electron cooling of ion beams employing a high-energy approach with RF-accelerated electron bunches was recently successfully implemented at BNL. It was used to cool ion beams in both collider rings with ion beams in collision. Electron cooling in RHIC became fully operational during the 2020 physics run and led to substantial improvements in luminosity. This presentation will discuss implementation, optimization and challenges of electron cooling for colliding ion beams in RHIC.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEXA02
About •	paper received ※ 18 May 2021 paper accepted ※ 15 June 2021 issue date ※ 13 August 2021
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WEXC03	Review of Superconducting Radio Frequency Gun	gun, SRF, cavity, operation	2556
	R. Xiang HZDR, Dresden, Germany
	The success of proposed high power free-electron lasers (FELs) and energy recovery linac (ERL) largely depends on the development of the electron source, which requires the best beam quality and CW operation. An elegant way to realize this average brilliance is to combine the high beam quality of mature normal conducting radio frequency photoinjector with the quick developing superconducting radio frequency technology, to build superconducting rf photoinjectors (SRF guns). In last decade, several SRF gun programs based on different approaches have achieved promising progress, even succeeded in routine operation at BNL and HZDR [,]. In the near future SRF guns are expected to play an important role for hard X-ray FEL facilities. In this contribution, we will review the design concepts, parameters, and the status of the major SRF gun projects. I. Petrushina et al., Phys. Rev. Lett. 124, 244801 **J. Teichert at al., Phys. Rev. Accel. Beams 24, 033401
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEXC03
About •	paper received ※ 19 May 2021 paper accepted ※ 28 June 2021 issue date ※ 11 August 2021
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WEPAB040	Characterization of Low Emittance Electron Beams Generated by Transverse Laser Beam Shaping	laser, emittance, flattop, electron	2690
	M. Groß, N. Aftab, P. Boonpornprasert, G.Z. Georgiev, J. Good, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, G. Shu, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany Y. Chen, G. Loisch DESY, Hamburg, Germany I. Will MBI, Berlin, Germany
	Linac based X-ray free electron laser demand a high beam quality from the electron source, therefore RF photoinjectors are used to generate the electron bunches for state of the art beam brightness. One important figure of merit for these injectors is the transverse emittance of the generated electron beam, which can be minimized by shaping the photocathode laser pulses. Best performance can be achieved with ellipsoidal laser pulses, but 3D shaping is technically challenging. Typically, a quasi-uniform transverse laser profile is truncated from the Gaussian profile generated by the laser with an aperture to reduce the transverse nonlinear space charge forces. This is investigated in detail by optimizing the laser transverse profile at the Photoinjector Test facility at DESY in Zeuthen (PITZ), where photoinjector R&D is conducted for the E-XFEL and FLASH free electron lasers at DESY in Hamburg. In this contribution we present experimental results at high acceleration gradients (up to 60 MV/m) for both 250 pC and 500 pC. For a bunch charge of 500 pC an emittance reduction of about 30% compared to the commonly used transverse flat-top laser distribution was achieved.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB040
About •	paper received ※ 17 May 2021 paper accepted ※ 02 June 2021 issue date ※ 31 August 2021
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WEPAB051	Beam Dynamics for a High Field C-Band Hybrid Photoinjector	electron, emittance, linac, gun	2714
	L. Faillace, F. Bosco, M. Carillo, L. Giuliano, M. Migliorati, A. Mostacci, L. Palumbo Sapienza University of Rome, Rome, Italy R.B. Agustsson, I.I. Gadjev, S.V. Kutsaev, A.Y. Murokh RadiaBeam, Marina del Rey, California, USA M. Behtouei, A. Giribono, B. Spataro, C. Vaccarezza INFN/LNF, Frascati, Italy A. Fukasawa, N. Majernik, J.B. Rosenzweig, O. Williams UCLA, Los Angeles, California, USA S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This work supported by DARPA GRIT under contract no. 20204571 and partially by INFN National Committee V through the ARYA project. In this paper, we present a new class of a hybrid photoinjector in C-Band. This project is the effort result of a UCLA/Sapienza/INFN-LNF/SLAC/RadiaBeam collaboration. This device is an integrated structure consisting of an initial standing-wave 2.5-cell gun connected to a traveling-wave section at the input coupler. Such a scheme nearly avoids power reflection back to the klystron, removing the need for a high-power circulator. It also introduces strong velocity bunching due to a 90° phase shift in the accelerating field. A relatively high cathode electric field of 120 MV/m produces a ~4 MeV beam with ~20 MW input RF power in a small foot-print. The beam transverse dynamics are controlled with a ~0.27 T focusing solenoid. We show the simulation results of the RF/magnetic design and the optimized beam dynamics that shows 6D phase space compensation at 250 pC. Proper beam shaping at the cathode yields a ~0.5 mm-mrad transverse emittance. A beam waist occurs simultaneously with a longitudinal focus of <400 fs rms and peak current >600 A. We discuss application of this injector to an Inverse-Compton Scattering system and present corresponding start-to-end beam dynamics simulations.
	Poster WEPAB051 [0.827 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB051
About •	paper received ※ 18 May 2021 paper accepted ※ 01 July 2021 issue date ※ 22 August 2021
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WEPAB092	Redesign of the Jefferson Lab -300 kV DC Photo-Gun for High Bunch Charge Operations	gun, high-voltage, simulation, electron	2802
	S.A.K. Wijethunga, J.R. Delayen, G.A. Krafft, G.G. Palacios Serrano ODU, Norfolk, Virginia, USA J.F. Benesch, J.R. Delayen, C. Hernandez-Garcia, G.A. Krafft, M.A. Mamun, M. Poelker, R. Suleiman JLab, Newport News, Virginia, USA
	Funding: The U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177, JSA initiatives fund program and Laboratory Directed Research and Development program. Production of high bunch charge beams for the Electron-Ion Collider (EIC) is a challenging task. High bunch charge (a few nC) electron beam studies at Jefferson Lab using an inverted insulator DC high voltage photo-gun showed evidence of space charge limitations starting at 0.3 nC, limiting the maximum delivered bunch charge to 0.7 nC for beam at -225 kV, 75 ps (FWHM) pulse width, and 1.64 mm (rms) laser spot size. The low extracted charge is due to the modest longitudinal electric field (Ez) at the photocathode leading to beam loss at the anode and downstream beam pipe. To reach the few nC high bunch charge goal, and to correct the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun the existing photo-gun was modified. This contribution discusses the electrostatic design of the modified photo-gun obtained using CST Studio Suite’s electromagnetic field solver. Beam dynamics simulations performed using General Particle Tracer (GPT) with the resulting electrostatic field map obtained from the modified electrodes confirmed the validity of the new design.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB092
About •	paper received ※ 20 May 2021 paper accepted ※ 02 June 2021 issue date ※ 19 August 2021
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WEPAB093	Space Charge Effects in Low Energy Magnetized Electron Beam	laser, electron, solenoid, space-charge	2806
	S.A.K. Wijethunga, J.R. Delayen, G.A. Krafft ODU, Norfolk, Virginia, USA J.F. Benesch, G.A. Krafft, M.A. Mamun, M. Poelker, R. Suleiman, S. Zhang JLab, Newport News, Virginia, USA
	Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and Laboratory Directed Research and Development program. Magnetized electron cooling is one of the major approaches towards obtaining the required high luminosity in the proposed Electron-Ion Collider (EIC). In order to increase the cooling efficiency, a bunched electron beam with a high bunch charge and high repetition rate is required. At Jefferson Lab, we generated magnetized electron beams with high bunch charge using a new compact DC high voltage photogun biased at -300 kV with bialkali-antimonide photocathode and a commercial ultra-fast laser. This contribution discusses how magnetization affects space charge dominated beams as a function of magnetic field strength, gun high voltage, and laser pulse width, and spot size in comparison with simulations performed using General Particle Tracer.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB093
About •	paper received ※ 19 May 2021 paper accepted ※ 08 June 2021 issue date ※ 23 August 2021
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WEPAB096	RF Testbed for Cryogenic Photoemission Studies	cryogenics, gun, electron, brightness	2810
	G.E. Lawler, A. Fukasawa, N. Majernik, J.B. Rosenzweig, A. Suraj, M. Yadav UCLA, Los Angeles, California, USA Z. Li SLAC, Menlo Park, California, USA M. Yadav The University of Liverpool, Liverpool, United Kingdom M. Yadav Cockcroft Institute, Warrington, Cheshire, United Kingdom
	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 40K, 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-IPAC2021-WEPAB096
About •	paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 21 August 2021
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WEPAB097	Initial Nanoblade-Enhanced Laser-Induced Cathode Emission Measurements	electron, laser, simulation, experiment	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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WEPAB098	Cryogenic Component and Material Testing for Compact Electron Beamlines	cryogenics, cavity, electron, gun	2818
	G.E. Lawler, N. Majernik, J.B. Rosenzweig UCLA, Los Angeles, California, USA
	Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE Contract DE-SC0020409 Cryogenic regimes of operation are, for various reasons, highly advantageous for normal conducting accelerator structures. Liquid cryogen-based systems are costly to implement and maintain. As a result, developing cryogenic test facilities at a smaller more cost effective scale using cryo-coolers is attractive. Before real implementations of a cryo-cooler based beamline, a significant amount of information is necessary regarding the behavior and properties of various components and materials at cryogenic temperatures. Finding this information lacking for our particular beamline case and by extension similar electron beamlines, we endeavor to generate a thorough beamline-relevant material and component properties down to the range of a liquid nitrogen temperatures (77 K) and the nominal operating temperature of a modest Gifford-McMahon cryocooler (45 K).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB098
About •	paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 18 August 2021
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WEPAB099	Near-Threshold Nonlinear Photoemission From Cu(100)	electron, laser, experiment, photon	2822
	C.J. Knill, S.S. Karkare Arizona State University, Tempe, USA H.A. Padmore LBNL, Berkeley, California, USA
	Funding: National Science Foundation Grant No. PHY-1549132 Photocathodes that have a low mean transverse energy (MTE) are crucial to the development of compact X-ray Free Electron Lasers (XFEL) and ultrafast electron diffraction (UED) experiments. For FELs, low MTE cathodes result in a lower requirement for electron energy when lasing at a defined energy, and for a defined electron energy result in lasing at higher energy. For UED experiments, low MTE cathodes give a longer coherence length, allowing measurements on larger unit cell materials. A record low MTE of 5 meV has been recently demonstrated from a Cu (100) surface when measured near the photoemission threshold and cooled down to 30 K with liquid Helium []. For UED and XFEL applications that require a high charge density, the low quantum efficiency of Cu (100) near threshold necessitates the use of a high laser fluence to achieve the desired charge density []. At high laser fluences the MTE is limited by nonlinear effects, and therefore it is necessary to investigate near photoemission threshold at these high laser fluences. In this paper we report on nonlinear, near-threshold photoemission from a Cu (100) cathode, and its effect on the MTE. S. Karkare et al, Phys. Rev. Lett. 125, 054801 (2020) ** J. Bae et al, J. Appl. Phys., 124, 244903 (2018)
	Poster WEPAB099 [0.829 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB099
About •	paper received ※ 19 May 2021 paper accepted ※ 21 July 2021 issue date ※ 20 August 2021
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WEPAB100	Heat Dissipation of Photocathodes at High Laser Intensities for a New DC Electron Source	electron, experiment, laser, operation	2826
	M.A. Dehn, K. Aulenbacher IKP, Mainz, Germany K. Aulenbacher HIM, Mainz, Germany K. Aulenbacher GSI, Darmstadt, Germany
	Funding: This project was supported by the German science ministry BMBF through the Verbundforschung Laser intensities of 1W or more are required to extract average beam currents of more than 10mA from photocathodes. Most of this laser power is converted into thermal load within the cathode and has to be dissipated to avoid excessive heating of the cathode and thus a significant reduction in lifetime. At Johannes Gutenberg-University Mainz, we are developing a new high current DC electron source operating at an energy of 100keV, where an efficient heat dissipation of the photocathode is achieved by a mechanical design of the supporting structure.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB100
About •	paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 26 August 2021
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WEPAB101	An Improved Model for Photoemission of Space Charge Dominated Picosecond Electron Bunches: Theory and Experiment	electron, experiment, laser, space-charge	2829
	S.M. Polozov, V.I. Rashchikov MEPhI, Moscow, Russia M. Krasilnikov DESY Zeuthen, Zeuthen, Germany
	The emission of a short highly charged electron bunch in a radiofrequency photogun is discussed. The traditional space charge limited emission numerical model is extended by an introduction of positively charged ions arising in the cathode region and dynamically changing during the emission. Estimates on the time characteristics of the charge migrating process in the semiconductor region are given. The numerical results are compared with the results of other numerical models and with experimental observations at the Photo Injector Test facility at DESY in Zeuthen (PITZ).
	Poster WEPAB101 [1.601 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB101
About •	paper received ※ 08 May 2021 paper accepted ※ 07 June 2021 issue date ※ 29 August 2021
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WEPAB102	Half-Metal Spin Filter for Highly Polarized Emission from GaAs Photocathodes	electron, polarization, lattice, hardware	2833
	S. Poddar, C.-J. Jing, E.J. Montgomery Euclid Beamlabs, Bolingbrook, USA P. Lukashev University of Northern Iowa, Cedar Falls, Iowa, USA C. Palmstrøm UCSB, Santa Barbara, California, USA M.L. Stutzman, S. Zhang JLab, Newport News, Virginia, USA
	Funding: Work supported by Department of Energy grant number DE-SC0020564. GaAs-based photocathodes are one of the major sources of spin-polarized electrons and are crucial for the upcoming Electron-Ion collider experiments which includes study of proton spin and spin parity violation in the standard model. The theoretical polarization limit in unstrained GaAs photocathodes is 50 % but only 35 % is routinely achieved in experiments. Spin selective filtering allows to boost the spin polarization beyond the 50 % theoretical limit. In this work, first-principle electronic calculations using standard Density Functional Theory are performed to predict possible Heusler alloy half-metal candidates to be used as spin-filter. Simulations are also performed to investigate the half-metallicity as function of the magnetic spin direction. Several devices are experimentally fabricated using dedicated Molecular Beam Epitaxy growth system. We implemented Quantum Efficiency and Polarization testing of these half-metal/GaAs heterostructures using a dedicated Mott polarimeter system. Photoemission can also be seen on magnetically switching the spin-filter direction accompanied by a change in sign of the asymmetry which is a qualitative proof of the spin-filtering effect.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB102
About •	paper received ※ 20 May 2021 paper accepted ※ 28 July 2021 issue date ※ 18 August 2021
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WEPAB103	Systematic Beam Parameter Studies at the Injector Section of FLUTE	laser, emittance, electron, quadrupole	2837
	T. Schmelzer, E. Bründermann, D. Hoffmann, I. Križnar, S. Marsching, A.-S. Müller, M.J. Nasse, R. Ruprecht, J. Schäfer, M. Schuh, N.J. Smale, P. Wesolowski, T. Windbichler KIT, Karlsruhe, Germany
	Funding: This work is supported by the DFG-funded Doctoral School "Karlsruhe School of Elementary and Astroparticle Physics: Science and Technology (KSETA)" FLUTE (Ferninfrarot Linac- und Test-Experiment) is a compact linac-based test facility for accelerator R&D and source of intense THz radiation for photon science. In preparation for the next experiments, the electron beam of the injector section of FLUTE has been characterized. In systematic studies the electron beam parameters, e.g., beam energy and emittance, are measured with several diagnostic systems. This knowledge allows the establishment of different operation settings and the optimization of electron beam parameters for future experiments.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB103
About •	paper received ※ 19 May 2021 paper accepted ※ 26 August 2021 issue date ※ 01 September 2021
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WEPAB104	Improving the Operational Lifetime of the CEBAF Photo-Gun by Anode Biasing	laser, simulation, electron, gun	2840
	J.T. Yoskowitz, G.A. Krafft, G.G. Palacios Serrano, S.A.K. Wijethunga ODU, Norfolk, Virginia, USA J.M. Grames, J. Hansknecht, C. Hernandez-Garcia, M. Poelker, M.L. Stutzman, R. Suleiman JLab, Newport News, Virginia, USA S.B. van der Geer Pulsar Physics, Eindhoven, The Netherlands
	Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. The operating lifetime of GaAs-based photocathodes in DC high voltage electron photo-guns is dominated by the ionization rate of residual beamline gas molecules. In this work, experiments were performed to quantify the improvement in photocathode charge lifetime by biasing the photo-gun anode with a positive voltage, which repels ions generated downstream of the anode. The photo-cathode charge lifetime improved by almost a factor of two when the anode was biased compared to the usual grounded configuration. Simulations were performed using the particle tracking code General Particle Tracer (GPT) with a new custom element. The simulation results showed that both the number and energy of ions play a role in the pattern of QE degradation. The experiment results and conclusions supported by GPT simulations will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB104
About •	paper received ※ 20 May 2021 paper accepted ※ 02 June 2021 issue date ※ 24 August 2021
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WEPAB105	Simulating Electron Impact Ionization Using a General Particle Tracer (GPT) Custom Element	electron, simulation, gun, high-voltage	2843
	J.T. Yoskowitz, G.A. Krafft ODU, Norfolk, Virginia, USA J.M. Grames JLab, Newport News, Virginia, USA G.R. Montoya Soto Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico C.A. Valerio ECFM-UAS, Culiacan, Sinaloa, Mexico S.B. van der Geer Pulsar Physics, Eindhoven, The Netherlands
	Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177, Consejo Nacional de Ciencia y Tecnología (CONACYT). A new C++ custom element has been developed with the framework of General Particle Tracer (GPT) to simulate electron impact ionization of residual gas molecules. The custom element uses Monte-Carlo routines to determine both the ion production rate and the secondary electron kinetic energy based on user-defined gas densities and theoretical values for the ionization cross section and the secondary electron differential cross section. It then uses relativistic kinematics to track the secondary electron, the scattered electron, and the newly formed ion after ionization. The ion production rate and the secondary electron energy distribution determined by the custom element have been benchmarked against theoretical calculations and against simulations made using the simulation package IBSimu. While the custom element was originally built for particle accelerator simulations, it is readily extensible to other applications. The custom element will be described in detail and examples of applications at the Thomas Jefferson National Accelerator Facility will be presented for ion production in a DC high voltage photo-gun.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB105
About •	paper received ※ 20 May 2021 paper accepted ※ 25 June 2021 issue date ※ 02 September 2021
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WEPAB106	Study on Durability Improvement of Cs-Te Photocathode by Means of Alkali Halide Protective Films	electron, experiment, ECR, laser	2847
	K. Ezawa, R. Fukuoka, Y. Koshiba, T. Tamba, M. Washio Waseda University, Tokyo, Japan K. Sakaue The University of Tokyo, Graduate School of Engineering, Bunkyo, Japan
	We have been conducting basic and applied research for generating high quality electron beams, using 1.6 cell laser photocathode RF-gun. In our laboratory, Cesium Telluride (Cs-Te), one of the semiconductor photocathodes, is used as an electron source for accelerator experiments. This semiconductor photocathode is known for high quantum efficiency (Q.E.) about 5~10% and 3-month 1/e lifetime. High Q.E. photocathodes can reduce the power requirement of the laser system, and long lifetime photocathodes can decrease the maintenance frequency, contributing to an efficient experimental environment. For these reasons, high Q.E. and long lifetime photocathodes are necessary in accelerator experiments. In order to produce robust photocathodes and extend the lifetime, we have conducted covering Cs-Te photocathodes with CsBr and CsI protective films. In this conference, we report the thickness dependency on the lifetime of Cs-Te photocathodes when we intentionally exposed oxygen gas to coated and non-coated Cs-Te photocathodes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB106
About •	paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 01 September 2021
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WEPAB109	Initial Study of GaN Thin Films for Photocathodes Prepared by Magnetron Sputtering on Copper Substrates	electron, plasma, gun, experiment	2850
	M. Vogel, X. Jiang, C. Wang University Siegen, Siegen, Germany P. Murcek, J. Schaber, R. Xiang HZDR, Dresden, Germany
	Funding: This research is funded by the Federal Ministry of Education and Research of Germany in the framework of BETH (project number 05K19PSB). On the path for high brightness electron beams, Gallium Nitride (GaN) is one promising candidate for a photo-cathode material. In this contribution, we report on the continuation of the study to optimize the crystallization quality and crystallography of Mg-doped GaN samples on copper substrates that are synthesized by RF magnetron sputtering. SEM and XRD results show that the pretreatment methods and the sputtering conditions (temperature, sputtering power, and partial pressure of the reactive gas) can both affect the morphology and crystal quality of GaN films. The initial QE measurements of these samples are done in our newly build in-situ QE measurement system and the first results of QE analyses done at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) are presented in a dedicated contribution. Part of this work was performed at the Micro- and Nanoanalytics Facility (MNaF) of the University of Siegen.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB109
About •	paper received ※ 19 May 2021 paper accepted ※ 09 June 2021 issue date ※ 29 August 2021
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WEPAB111	Controlled Degradation by Oxygen Exposure in the Performance of a Ag (100) Single-Crystal Photocathode	experiment, electron, cryogenics, emittance	2856
	L.A.J. Soomary, C.P. Welsch The University of Liverpool, Liverpool, United Kingdom L.B. Jones, T.C.Q. Noakes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	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 including the work function, intrinsic emittance, and quantum efficiency of the photocathode. These factors in turn define the electron beam performance which is measurable as normalized 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 electron source community. As such, pure metal photocathodes and their performance at UV wavelengths are of interest as seen at the LCLS at SLAC and CLARA at Daresbury. We present performance data for an Ag (100) single-crystal photocathode under illumination at 266 nm wavelength, with known levels of surface roughness, using our Transverse Energy Spread Spectrometer (TESS)** both at room and cryogenic temperatures. Crucially our data shows the effect of progressive degradation in the photo-cathode performance as a consequence of exposure to controlled levels of oxygen. * D.H. Dowell, et al., Nucl. Instr. and Meth. A (2010), doi:10.1016/j.nima.2010.03.104 Appl. Phys. Lett. 89, 224103 (2006); doi:10.1063/1.2387968 * Proc. FEL’13, TUPPS033, 290-293
	Poster WEPAB111 [0.866 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB111
About •	paper received ※ 20 May 2021 paper accepted ※ 22 June 2021 issue date ※ 21 August 2021
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WEPAB112	Performance Characterisation of a Cu (100) Single-Crystal Photocathode	electron, emittance, experiment, photon	2860
	L.A.J. Soomary, D.P. Juarez-Lopez, C.P. Welsch The University of Liverpool, Liverpool, United Kingdom L.B. Jones, T.C.Q. Noakes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The search for high performance photocathode electron sources is a priority in the accelerator science community. The surface characteristics of a photocathode define important factors of the photoemission including the intrinsic emittance, the quantum efficiency and the work function of the photocathode. These factors in turn define the electron beam performance which are measurable as emittance, brightness and energy spread. We have used ASTeC’s Multiprobe (SAPI)* to characterise and analyse photocathode performance using multiple techniques including XPS, STM, and LEED imaging, and their Transverse Energy Spread Spectrometer (TESS)** to measure mean transverse energy (MTE). We present characterisation measurements for a Cu (100) single-crystal photocathode sample with data from SAPI confirming the crystallographic face and showing surface composition and roughness, supported by data from TESS showing the photocathode electron beam energy spread. * B.L. Militsyn, 4-th EuCARD2 WP12.5 meeting, Warsaw, 14-15 March 2017 **Proc. FEL’13, TUPPS033, 290-293
	Poster WEPAB112 [0.814 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB112
About •	paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 25 August 2021
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WEPAB115	Beam Preparation with Temporally Modulated Photocathode Laser Pulses for a Seeded THz FEL	FEL, laser, electron, simulation	2866
	G.Z. Georgiev, N. Aftab, P. Boonpornprasert, J. Good, M. Groß, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, A. Lueangaramwong, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach DESY Zeuthen, Zeuthen, Germany N. Chaisueb Chiang Mai University, Chiang Mai, Thailand W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	The need for carrier-envelope-phase (CEP) stable THz pump pulses is recognized at many pump-probe experiments at the European XFEL. At the Photo Injector Test Facility at DESY in Zeuthen (PITZ), a proof-of-principle experiment of an accelerator-based THz FEL source is in preparation. Since the CEP stability of FEL pulses is not guaranteed in the SASE regime, a seeding scheme is needed. A common scheme for seeding is to drive the microbunching process with external laser pulses, which are power-limited in the THz range. Alternatively, a pre-bunched beam, generated for example by applying a temporally modulated photocathode laser pulse, can be used to drive the FEL. The beam dynamics with such a seeding method are studied with ASTRA tracking code simulations with space-charge forces as well as experimentally. The results of these studies are shown and discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB115
About •	paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 21 August 2021
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WEPAB138	Superconducting RF Gun with High Current and the Capability to Generate Polarized Electron Beams	gun, SRF, electron, cavity	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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WEPAB149	The RF Gun for the Siberian Circular Light Source "SKIF"	cavity, gun, electron, linac	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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WEPAB157	Understanding the Growth Dynamics Cs-Sb Thin Films via In-Situ Characterization Techniques: Towards Epitaxial Alkali Antimonide Photocathodes	electron, brightness, lattice, scattering	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	electron, gun, injection, acceleration	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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WEPAB169	Towards Ultra-Smooth Alkali Antimonide Photocathode Epitaxy	lattice, interface, emittance, electron	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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WEPAB256	Three-Dimensional Space Charge Oscillations in a Hybrid Photoinjector	emittance, plasma, simulation, electron	3240
	M. Carillo, M. Behtouei, F. Bosco, L. Faillace, A. Giribono, L. Giuliano, M. Migliorati, A. Mostacci, L. Palumbo Sapienza University of Rome, Rome, Italy L. Ficcadenti INFN-Roma, Roma, Italy J.B. Rosenzweig UCLA, Los Angeles, California, USA B. Spataro, C. Vaccarezza INFN/LNF, Frascati, Italy
	Funding: This work supported by DARPA GRIT under contract no. 20204571 and partially by INFN National committee V through the ARYA project. A new hybrid C-band photo-injector, consisting of a standing wave RF gun connected to a traveling wave structure, operating in a velocity bunching regime, has shown to produce an extremely high brightness beam with very low emittance and a very high peak current through a simultaneous compression of the beam in the longitudinal and transverse dimensions. A beam slice analysis has been performed in order to understand the evolution of the relevant physical parameters of the beam in the longitudinal and transverse phase spaces along the structure. A simple model for the envelope equation has been developed to describe the beam behavior in this particular dynamics regime that we term "triple waist", since all three dimensions reach a minimum condition almost simultaneously. The model analyzes the transverse envelope dynamics at the exit of the hybrid photo-injector, in the downstream drift where the triple waist occurs. The analytical solutions obtained from the envelope equation are compared with the simulations, showing a good agreement. Finally, these results have been analyzed also in terms of plasma oscillation to obtain a further physical interpretation of the beam dynamics.
	Poster WEPAB256 [1.162 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB256
About •	paper received ※ 19 May 2021 paper accepted ※ 21 July 2021 issue date ※ 12 August 2021
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WEPAB290	Pointing Stabilization Algorithms Explored and Implemented with the Low Energy RHIC Electron Cooling Laser	laser, operation, electron, feedback	3336
	L.K. Nguyen 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 electron beam for the Low Energy RHIC electron Cooler (LEReC) at Brookhaven National Laboratory (BNL) is generated by a high-power fiber laser illuminating a photocathode, with a total propagation distance of 34 m separating the laser output and the photocathode. This propagation is facilitated by three independent laser tables that have varying responses to changes in time of day, weather, and season. Alignment drifts induced by these environmental changes are mitigated by an active "slow" pointing stabilization system found along the length of the transport, and this in-house system was commissioned as part of the full laser transport in 2019, as previously reported. In 2020, the system became fully operational alongside LEReC, the world’s first electron cooler in a collider, and helped establish the transverse stability of the electron beam required for cooling. A summary of the different slow stabilization algorithms, which were continually refined during the run in order to achieve long-term center-of-mass stability of the laser spot on the photocathode to within 10 microns RMS, is provided. L. K. Nguyen et al., "Active Pointing Stabilization Techniques Applied to the Low Energy RHIC Electron Cooling Laser Transport at BNL", presented at NAPAC’19, paper THYBA6.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB290
About •	paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 30 August 2021
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WEPAB296	A Klystron Phase Lock Loop for RF System at TPS Booster Ring	controls, klystron, LLRF, injection	3354
	F.Y. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.D. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh, T.-C. Yu NSRRC, Hsinchu, Taiwan
	In TPS booster ring, the DLLRF is used to controlled the ramping gap voltage and also the energy saving module is applied to save power while the ring does not inject beam. But we occurred to have a problem of PI saturation due to a large phase change when the energy saving module working. The energy saving module switches the anode voltage of the klystron from high to low level to decrease the cathode current while the ring does not inject and do the opposite while the ring injects. This action causes a large phase change of the transmitter and leads the PI controller to work in the wrong direction. We add a klystron phase loop to solve this situation.
	Poster WEPAB296 [0.792 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB296
About •	paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 31 August 2021
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WEPAB308	Measurement-Based Surrogate Model of the SLAC LCLS-II Injector	laser, simulation, network, controls	3395
	L. Gupta, Y.K. Kim University of Chicago, Chicago, Illinois, USA A.L. Edelen, C.E. Mayes, A.A. Mishra, N.R. Neveu SLAC, Menlo Park, California, USA
	Funding: This project was funded by the DOE SCGSR Program. There is significant effort within particle accelerator physics to use machine learning methods to improve modeling of accelerator components. Such models can be made realistic and representative of machine components by training them with measured data. These models could be used as virtual diagnostics or for model-based control when fast feedback is needed for tuning to different user settings. To prototype such a model, we demonstrate how a machine learning based surrogate model of the SLAC LCLS-II photocathode injector was developed. To create machine-based data, laser measurements were taken at the LCLS using the virtual cathode camera. These measurements were used to sample particles, resulting in realistic electron bunches, which were then propagated through the injector via the Astra space charge simulation. By doing this, the model is not only able to predict many bulk electron beam parameters and distributions which are often hard to measure or not usually available to measure, but the predictions are more realistic relative to traditionally simulated training data. The methods for training such models, as well as model capabilities and future work are presented here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB308
About •	paper received ※ 26 May 2021 paper accepted ※ 27 July 2021 issue date ※ 21 August 2021
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WEPAB327	Sheet Electron Probe for Beam Tomography	electron, proton, diagnostics, simulation	3437
	V.G. Dudnikov, M.A. Cummings, G. Dudnikova Muons, Inc, Illinois, USA
	Funding: Work is funded by DOE SBIR grant DE-SC0021581 An electron beam probe has been successfully used for the determination of accelerated particle density distributions. However, the apparatus used for this diagnostic had a large size and complex design which limit the broad use of this diagnostic for tomography of accelerated bunches. We propose a new approach to electron beam tomography: we will generate a continuous sheet of electrons. As the ion beam bunches pass through the sheet, they cause distortions in the distribution of sheet electrons arriving at CCD device on the other side of the beam that is interpreted to give a continuous measurement of the beam profile. The apparatus to generate the sheet beam is a strip cathode, which, compared to the scanning electron beam probe, is smaller, has a simpler design and less expensive manufacturing, has better magnetic shielding, has higher sensitivity, higher resolution, has better accuracy of measurement and better time resolution. With this device, it is possible to develop almost ideal tomography diagnostics of bunches in linear accelerators and in circular accelerators and storage rings.
	Poster WEPAB327 [0.640 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB327
About •	paper received ※ 19 May 2021 paper accepted ※ 15 July 2021 issue date ※ 25 August 2021
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WEPAB328	Rapid Surface Microanalysis Using a Low Temperature Plasma	plasma, electron, radiation, target	3440
	V.G. Dudnikov, M.A. Cummings, R.P. Johnson Muons, Inc, Illinois, USA
	There is a need for rapid, high-resolution (micron or sub-micron) scanning of surfaces of special nuclear materials (SNM) and surrogate materials to locate and identify regions of abnormalities. One technique that is commonly used to analyze the composition of solid surfaces and thin films is secondary-ion mass spectrometry (SIMS). SIMS devices are very complex and expensive. We propose to develop simpler, less expensive surface analysis devices, based on glow-discharge optical emission spectroscopy (GOES) that can provide excellent spatial resolution. Ions from a plasma discharge sputtered atoms from the surface and the discharge electrons effectively excite and ionize the sputtered atoms. GOES uses the light emitted by the excited particles for quantitative analysis. In the GOES device, the ion flux is extracted from the gas-discharge plasma and focused to a micron size on the sample, providing very local sputtering and local elemental analysis. The radiation from the sputtered atoms is passed through an optical fiber to an optical spectrometer and recorded. To register the distribution of elements over the sample, the sample is scanned electro-mechanically.
	Poster WEPAB328 [0.385 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB328
About •	paper received ※ 19 May 2021 paper accepted ※ 29 July 2021 issue date ※ 24 August 2021
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WEPAB336	Aluminum Vacuum Chamber for the Sirius Commissioning Undulators	undulator, vacuum, MMI, storage-ring	3467
	B.M. Ramos, O.R. Bagnato, R.O. Ferraz, H.G. Filho, P.P.S. Freitas, G.R. Gomes, P.H. Lima, R.F. Oliveira, T.M. Rocha, F. Rodrigues, R.M. Seraphim, D.R. Silva, M.B. Silva LNLS, Campinas, Brazil
	Sirius is a 3 GeV fourth generation light source under commissioning by the Brazilian Synchrotron Light Laboratory (LNLS). Compact Linear Polarizing Undulators with magnet vertical aperture of 8 mm have been used for the commissioning of some beam lines. Extruded aluminum vacuum chambers having small vertical aperture of 6 mm and horizontal aperture of 40 mm, were built. This paper details the design and manufacturing processes of a complete chamber and its installation procedure at the storage ring. Challenges regarding the precision machining of the 0.5 mm wall thickness, TIG welding for aluminum, NEG coating for small apertures will also be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB336
About •	paper received ※ 18 May 2021 paper accepted ※ 17 August 2021 issue date ※ 25 August 2021
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WEPAB379	Photocathode Laser Development for Superconducting X-Ray Free Electron Lasers at DESY	laser, FEL, operation, electron	3599
	C. Li, O. Akcaalan, U. Grosse-Wortmann, I. Hartl, C. Mohr, M. Seidel, H. Tuennermann, C. Vidoli, L. Winkelmann DESY, Hamburg, Germany M. Frede, O. Puncken neoLASE GmbH, Hanover, Germany
	Funding: Deutsches Elektronen-Synchrotron, Hamburg, 22609, Germany Modern X-Ray Free-Electron Lasers (XFEL) are a key tool to enable a variety of scientific research. Those large-scale machines rely on robust and reliable deep ultraviolet (DUV) laser sources to drive electrons from their RF photocathode gun. In this paper we present a new photocathode laser prototype, which offers more flexibility in duration and shape of the 257.5 nm pulses for driving the CsTe Photocathodes of DESY’s superconducting burst-mode FELs. The laser matches the FEL pulse structure, which are 800 µs bursts at up to 4.5 MHz intraburst-rate with 10 Hz burst-repetition-rate. In a first version the system will offer variable DUV pulse durations, tunable from 1 ps to 20 ps to address different operational regimes of the XFEL. The laser system comprises a high-resolution spectral shaper with the option of generating flat-top DUV pulses for reducing electron-beam emittance at a later version. The laser is constructed in a hybrid Yb:fiber and Yb:YAG architecture. Our prototype delivers 180 uJ pulse energy at 1030 nm and 1 MHz intra-burst rate and we demonstrated conversion of 50µJ of the NIR beam to DUV, resulting 11.5µJ at 21ps (FWHM) and 6.15 µJ at 1.05 ps (FWHM) pulse duration.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB379
About •	paper received ※ 27 May 2021 paper accepted ※ 02 July 2021 issue date ※ 29 August 2021
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WEPAB385	Beam Dynamic Analysis of RF Modulated Electron Beam Produced by Gridded Thermionic Guns	electron, gun, emittance, linac	3618
	G. Adam University of Strathclyde, Glasgow, United Kingdom A.W. Cross, L. Zhang USTRAT/SUPA, Glasgow, United Kingdom B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom B.L. Militsyn Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Funding: Science and Technology Facilities Council (STFC) U.K training grant, industrial case with TMD Ltd, UK ST/R002141/1 "Accelerators for Security, healthcare and Environmental applications ". A thermionic cathode gridded electron gun used in injectors for different types of circular and linear particle accelerators and for energy recovery configurations was studied. Both theory and numerical simulation were used to explore the relationship between the bunch charge and bunch length. The electron gun is based on a Pierce-type geometry. It was initially designed using Vaughan synthesis followed by optimization using a 2D electron trajectory solver TRAK. After optimization, the grid in front of the cathode was inserted and the RF field was introduced through a coaxial waveguide structure. The complete gun was simulated using the PIC code MAGIC. High duty cycle operations at frequencies 1.5 GHz and 3.0 GHz, were investigated using different combinations of both the bias and the RF voltage applied between the cathode and the grid. The beam dynamics results from the PIC showed that a minimum bunch length of 10⁶ ps could be achieved with a bunch charge of 33 pC when the driving RF frequency was 1.5 GHz. Operating at the higher RF frequency of 3GHz did not significantly reduce the bunch length. The normalized emittance of about 5.6 mm-mrad was demonstrated in PIC simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB385
About •	paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 24 August 2021
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THXC07	Adaptive Control of Klystron Operation Parameters for Energy Saving at Storage Ring of TPS	klystron, operation, controls, storage-ring	3748
	T.-C. Yu, F.Y. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.D. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh NSRRC, Hsinchu, Taiwan
	To satisfy maximum beam current operation in the storage ring of TPS, the operation parameters of both RF transmitters are set to be able to generate its maxi-mum RF power in daily usage. Under such condition, the klystrons can deliver any power below 300kW at constant AC power consumption which is about 520-530 kW. Hence, the AC power usage is independent of the required RF output power. To best utilize the avail-able AC power based on the required RF power, an adaptive control methodology is proposed here to change the operation parameters of the klystron, cath-ode voltage and anode voltage, according to the pre-sent RF power. The corresponding operation parame-ters are applied by the prior tested table which maps the operation parameters with the different saturation RF power. The test results show that the saved energy can be 32% to 11% from 30mA to 450mA for both RF plants as comparing to constant operation parameters of 1047 kW AC power.
	Slides THXC07 [1.241 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXC07
About •	paper received ※ 19 May 2021 paper accepted ※ 06 July 2021 issue date ※ 29 August 2021
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THPAB022	Possibilities for Upgrading to Polarized SuperKEKB	electron, polarization, experiment, lattice	3799
	Z.J. Liptak, M. Kuriki HU/AdSM, Higashi-Hiroshima, Japan J.M. Roney Victoria University, Victoria, B.C., Canada
	The SuperKEKB accelerator is currently in operation in Tsukuba, Japan, with a planned long shutdown in 2026. Among the possible upgrades being considered during this period is the change to a polarized electron beam in the High Energy Ring. Such a change would require modifications in the source generation and transport, geometrical and lattice variations to provide spin rotation, and polarimetry. A Polarized SuperKEKB Working Group has been formed from members of the Belle II experiment and the SuperKEKB accelerator team to investigate the possibilities and challenges of these modifications. This talk lays out the goals of the proposed upgrade, considers the necessary changes to the existing accelerator and their feasibility and lays out the physics motivation behind such an effort.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB022
About •	paper received ※ 19 May 2021 paper accepted ※ 23 July 2021 issue date ※ 15 August 2021
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THPAB082	Recent Operational Experience with Thermionic RF Guns at the APS	gun, linac, operation, injection	3959
	Y. Sun, M. Borland, G.I. Fystro, X. Huang, H. Shang ANL, Lemont, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 The electron beam at the Argonne Advanced Photon Source (APS) is generated from an S-band thermionic RF gun. There are two locations at the frontend of the linac where thermionic RF guns are installed – RG1 and RG2. Three so-called generation-III guns are available, two are installed at RG1 and RG2, one is a spare. In recent years, these guns are showing signs of aging after over a couple of decades of operations. RF trips started to occur, and we had to reduce the nominal operating rf power to alleviate the problem. In addition, beam generated by RG1 suffers from low transportation efficiency from the gun to the linac, and beam trajectory is unstable which results in charge instabilities. Recently, APS obtained a new type of prototype gun and it was beam commissioned in the linac. In this paper, we report our operational experience with these thermionic rf guns including thermionic-cathode beam extraction, gun front-end optimization for maximum charge transmission through the linac, linac lattice setup to match beam for injection into the Particle Accumulator Ring (PAR) and optimization for maximum PAR injection efficiency.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB082
About •	paper received ※ 19 May 2021 paper accepted ※ 28 July 2021 issue date ※ 16 August 2021
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THPAB129	Beam Dynamics Simulations in a High-Gradient X-Band Photoinjector	gun, emittance, electron, linac	4013
	W.H. Tan, P. Piot Northern Illinois University, DeKalb, Illinois, USA G. Chen, S.V. Kuzikov Euclid TechLabs, Solon, Ohio, USA G. Chen IIT, Chicago, Illinois, USA G. Ha, C.-J. Jing ANL, Lemont, Illinois, USA C.-J. Jing Euclid Beamlabs, Bolingbrook, USA
	A high-gradient X-band (11.7-GHz) photoinjector was recently developed by Euclid Techlabs and is in its commissioning phase at the Argonne Wakefield Accelerator (AWA). This contribution discuss the beam-dynamics modeling of the photoinjector system comprising an RF gun and linac section. We especially discuss beam-dynamics optimization of setup for an integrated proof-of-principle experiments. We also discuss the use of such a photoinjector as a witness-bunch source for a future high-gradient collinear-wakefield accelerator experiments at the AWA. * S. V. Kuzikov, et al. these proceedings.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB129
About •	paper received ※ 20 May 2021 paper accepted ※ 14 July 2021 issue date ※ 31 August 2021
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THPAB141	Novel Design of a HVDC Magnetized Electron Source	solenoid, permanent-magnet, gun, simulation	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	electron, photon, emittance, vacuum	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	gun, cavity, coupling, simulation	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	electron, cavity, FEM, gun	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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THPAB156	Built-in Thermionic Electron Source for an SRF Linacs	cavity, electron, gun, SRF	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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THPAB221	Multi-Objective Optimization with ACE3P and IMPACT	cavity, simulation, lattice, interface	4223
	D.A. Bizzozero, J. Qiang LBNL, Berkeley, California, USA L. Ge, Z. Li, C.-K. Ng, L. Xiao SLAC, Menlo Park, California, USA
	Funding: This work is supported by the Director of the Office of Science of the US Department of Energy under contracts DE-AC02-05-CH11231 and DE-AC02-76-SF00515. Photo injector design is an important consideration in the construction of next-generation accelerators. In current injector optimization, components (e.g. RF cavities) are individually shape-optimized for performance subject to requirements such as peak surface field, shunt impedance, and resonant frequency. Once these component shapes are determined, beam dynamics simulations optimize the injector lattice by adjusting parameters such as the amplitude and phase of the driving fields. However, this form of beam dynamics optimization is restricted by the fixed geometry and field profile of the components. To optimize accelerator design more generally, a coupled optimization of the cavity shape and beam parameters is required. For this coupled optimization problem, we have created an integrated ACE3P-IMPACT workflow. Within this workflow, component geometries are adjusted, field modes are computed with Omega3P (a module in the ACE3P suite), and beam dynamics are simulated with IMPACT-T. This workflow is encapsulated into a multi-objective optimization algorithm using the DEAP* and libEnsemble** Python libraries to yield a Pareto-optimal set of solutions for a simple injector model. * F.-A. Fortin et al, DEAP: Evolutionary Algorithms Made Easy, J Mach Learn Res, 13, 2171-2175, July 2012 ** S. Hudson et al, libEnsemble User Manual, Argonne National Laboratory, Rev 0.7.1, 2020
	Poster THPAB221 [1.842 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB221
About •	paper received ※ 19 May 2021 paper accepted ※ 02 August 2021 issue date ※ 26 August 2021
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THPAB229	Energy-Binning Fast Multipole Method for Electron Injector Simulations	space-charge, simulation, electron, multipole	4244
	S.A. Schmid, H. De Gersem, E. Gjonaj TEMF, TU Darmstadt, Darmstadt, Germany
	In a high brilliance electron injector, small beam energy and large charge density give rise to strong space charge effects. Furthermore, a large relative energy spread during the beam generation modifies the space charge interaction between different regions of the particle bunch. Therefore, modeling the phase space evolution in an electron injector requires a numerically efficient particle tracking code that can handle space charge interactions of spatially and energetically strongly inhomogeneous particle distributions. We implemented an energy-binning scheme for a meshless fast multipole method (FMM). The energy-binning approximates the momentum distribution of the beam by assigning particles to adaptive tree structures defined at different Lorentz frames. Based on the tree structures, the FMM computes a hierarchical approximation for the space charge interaction of the particle bunch. We use the energy-binning FMM to simulate the beam generation in the photoinjector of the European XFEL developed at DESY-PITZ. Furthermore, we present numerical convergence and performance studies and compare the simulation results to direct particle-particle methods.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB229
About •	paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 13 August 2021
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THPAB313	Drive Laser System for Shanghai Soft X-Ray Free Electron Laser	laser, FEL, electron, free-electron-laser	4403
	L. Feng, C.L. Li, B. Liu, J.G. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China X. Lu ANL, Lemont, Illinois, USA X.T. Wang, W.Y. Zhang Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
	In this paper, we introduce the design and layout of the drive laser of Shanghai Soft X-ray Free Electron Laser (SXFEL). It is known that the temporal and spatial distribution of the drive laser is crucial for high-quality electron beams. The drive laser provides the laser pulse of 266nm wavelength and 8ps pulse duration for the photocathode, as well as 400nm wavelength, 2-20ps tunable pulse duration for the laser heater. For this purpose, there are mainly four parts in such system, including a third-harmonic generation device, pulse stretcher, image transmitted system, and laser optical module for laser heater. Finally, the measured results of the electron beam under this drive laser system are presented and discussed.
	Poster THPAB313 [0.691 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB313
About •	paper received ※ 20 May 2021 paper accepted ※ 15 July 2021 issue date ※ 10 August 2021
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THPAB331	High-Power Test of a Highly Over-Coupled X-Band RF Gun Driven by Short RF Pulses	gun, electron, wakefield, flattop	4432
	J.H. Shao, D.S. Doran, W. Liu, J.G. Power, C. Whiteford, E.E. Wisniewski ANL, Lemont, Illinois, USA C.-J. Jing, S.V. Kuzikov Euclid TechLabs, Solon, Ohio, USA X. Lu, P. Piot, W.H. Tan Northern Illinois University, DeKalb, Illinois, USA
	Beam brightness, a key figure of merit of RF photocathode guns, can be improved by increasing the cathode surface field which suppresses emittance growth from space charge. The surface field in normal-conducting structures is mainly limited by RF breakdown and it has been experimentally discovered that RF breakdown rate exponentially depends on RF pulse length. A highly over-coupled 1.5-cell X-band photocathode gun has been developed to be powered by 9 ns RF pulses with 3 ns rising time, 3 ns flat-top, and 3 ns falling time generated by an X-band metallic power extractor. In the recent experiment at Argonne Wakefield Accelerator facility, cathode surface field up to ~350 MV/m with a low breakdown rate has been obtained under ~250 MW input power. Strong beam loading from dark current was observed during RF conditioning and quickly recovered to a negligible level after the gun reached the maximum gradient. Detailed high-power test results and data analysis will be reported in this manuscript.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB331
About •	paper received ※ 25 May 2021 paper accepted ※ 14 July 2021 issue date ※ 10 August 2021
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THPAB344	Magneto-Optical Trap Cathode for High Brightness Applications	electron, laser, gun, emittance	4466
	V.S. Yu, C.E. Hansel, G.E. Lawler, M. Mills, J.B. Rosenzweig UCLA, Los Angeles, California, USA J.I. Mann PBPL, Los Angeles, USA
	Funding: This work was performed with support of the US Department of Energy under Contract No. DE-SC0020409 and the National Science Foundation under Grant No. PHY-1549132 Electron bunches extracted from magneto-optical traps (MOTs) via femtosecond photo-ionization and electrostatic acceleration can have significantly lower transverse emittance than emissions from traditional metal cathodes. Such MOT cathodes, however, have two drawbacks: the need for multiple trapping lasers and the limit to ~MV/m fields. Designs exist for MOTs which only require one trapping laser. Our RF simulations in High-Frequency Structure Simulator (HFSS) indicate that the cone MOT is the only one compatible with high gradient RF cavities. We present the combination of the two, an RF cavity with a cone-MOT as part of its geometry. It only requires one trapping laser and can use much higher fields. The geometry of the chamber is compatible with a wide range of MOT species, which allows the search for one which is compatible with copper cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB344
About •	paper received ※ 19 May 2021 paper accepted ※ 29 July 2021 issue date ※ 31 August 2021
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THPAB349	Feed-Forward Neural Network Based Modelling of an Ultrafast Laser for Enhanced Control	laser, network, controls, electron	4478
	A. Aslam, M. Martínez-Ramón, S.D. Scott UNM-ECE, Albuquerque, USA S. Biedron Argonne National Laboratory, Office of Naval Research Project, Argonne, Illinois, USA S. Biedron Element Aero, Chicago, USA S. Biedron UNM-ME, Albuquerque, New Mexico, USA M. Burger, J. Murphy NERS-UM, Ann Arbor, Michigan, USA K.M. Krushelnick, J. Nees, A.G.R. Thomas University of Michigan, Ann Arbor, Michigan, USA Y. Ma IHEP, Beijing, People’s Republic of China Y. Ma Michigan University, Ann Arbor, Michigan, USA
	Funding: Acknowledgements: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under award number DE-SC0019468. The applications of machine learning in today’s world encompass all fields of life and physical sciences. In this paper, we implement a machine learning based algorithm in the context of laser physics and particle accelerators. Specifically, a neural network-based optimisation algorithm has been developed that offers enhanced control over an ultrafast femtosecond laser in comparison to the traditional Proportional Integral and derivative (PID) controls. This research opens a new potential of utilising machine learning and even deep learning techniques to improve the performance of several different lasers and accelerators systems.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB349
About •	paper received ※ 20 May 2021 paper accepted ※ 02 July 2021 issue date ※ 19 August 2021
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Paper

Title

Other Keywords

Page

MOXC02

Improved Lifetime of a High Spin Polarization Superlattice Photocathode

electron, polarization, gun, vacuum

31

L. Cultrera
BNL, Upton, New York, USA

Funding: Department of Energy under grant DE-SC0012704
Highly spin polarized electron beams are required for the operation of a wide range of accelerators and instruments. The production of such electrons requires the use of Negative Electron Affinity (NEA) activated GaAs-based cathodes operated in photoelectron guns. Because of their extreme sensitivity to poor vacuum conditions the degradation of the photoemission process is so strong that NEA activated GaAs-based photocathodes can only survive in the extreme vacuums typical of DC gun. State-of-the-art on photocathode technology for spin polarized beam productions are summarized. Recent results on the use of robust NEA coating based on the Cs-Te and Cs-Sb leading to improved operational lifetime of a high spin polarization photocathode are reviewed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOXC02

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paper received ※ 20 May 2021 paper accepted ※ 19 July 2021 issue date ※ 11 August 2021

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MOPAB138

Dielectric Wakefield Acceleration with a Laser Injected Witness Beam

wakefield, laser, experiment, simulation

481

G. Andonian, T.J. Campese
RadiaBeam, Santa Monica, California, USA
N.M. Cook
RadiaSoft LLC, Boulder, Colorado, USA
D.S. Doran, G. Ha, J.G. Power, J.H. Shao, E.E. Wisniewski
ANL, Lemont, Illinois, USA
W.J. Lynn, N. Majernik, J.B. Rosenzweig, V.S. Yu
UCLA, Los Angeles, California, USA

Funding: Work supported by DOE grant DE-SC0017690
The plasma photocathode concept, whereby a two-species gas mixture is used to generate a beam -driven accelerating wakefield and a laser-ionized generation of a witness beam, was recently experimentally demonstrated. In a variation of this concept, a beam-driven dielectric wakefield accelerator is employed, filled with a neutral gas for laser-ionization and creation of a witness beam. The dielectric wakefields, in the terahertz regime, provide comparatively modest timing requirements for the injection phase of the witness beam. In this paper, we provide an update on the progress of the experimental realization of the hybrid dielectric wakefield accelerator with laser injected witness beam at the Argonne Wakefield Accelerator (AWA), including engineering considerations for gas delivery, and preliminary simulations.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB138

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paper received ※ 19 May 2021 paper accepted ※ 17 June 2021 issue date ※ 15 August 2021

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MOPAB153

Laser Microfabrication for Accelerator Applications

laser, FEM, simulation, emittance

535

S.P. Antipov, S.V. Kuzikov
Euclid TechLabs, Solon, Ohio, USA
A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia

Laser microfabrication allows high precision ablation of materials at sub-mm scale. When laser pulse length is shorter than about 10 picoseconds the heat affected zone is minimized and ablation occurs without melting. Work-pieces processed in this fashion exhibit less structural damage and are expected to have a higher damage thresholds. In this paper we will review several case studies of laser-microfabricated components for accelerator and x-ray applications. Ablated materials include diamond, quartz, tungsten, copper, YAG:Ce and silicon.

Poster MOPAB153 [2.781 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB153

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paper received ※ 20 May 2021 paper accepted ※ 01 July 2021 issue date ※ 31 August 2021

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MOPAB257

Effects of Mode Launcher on Beam Dynamics in Next Generation High Brightness C-Band Guns

gun, emittance, simulation, electron

813

A. Giribono, D. Alesini, F. Cardelli, G. Di Raddo, M. Ferrario, A. Gallo, J. Scifo, C. Vaccarezza, A. Vannozzi
INFN/LNF, Frascati (Roma), Italy
G. Castorina
AVO-ADAM, Meyrin, Switzerland
L. Ficcadenti
INFN-Roma, Roma, Italy
G. Muti
Sapienza University of Rome, Rome, Italy
G. Pedrocchi
SBAI, Roma, Italy

High-brightness RF photo-injectors plays nowadays a crucial role in the fields of radiation generation and advanced acceleration schemes. A high gradient C-band photoinjector consisting of a 2.5 cell gun followed by TW sections is here proposed as an electron source for radiation user facilities. The paper reports on beam dynamics studies in the RF injector and illustrates the effects on the beam quality of the mode launcher with a focus on the compensation of the quadrupole RF components.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB257

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paper received ※ 19 May 2021 paper accepted ※ 08 June 2021 issue date ※ 12 August 2021

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TUPAB033

Photocathode Stress Test Bench at INFN LASA

laser, gun, electron, high-voltage

1413

D. Sertore, D. Giove, G. Guerini Rocco, 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

In the framework of the preparatory activities to the BriXSino project, a test bench for testing Cs₂Te photocathode at 100 MHz laser repetition rate has been installed at INFN LASA. This high repetition operation mode is foreseen to be the base operation mode of BriXSino and a qualification of the Cs₂Te photocathodes is a key component. While we are not at full specification due to the limited HV of the present DC gun, we discuss the status of the test bench and the initial results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB033

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paper received ※ 19 May 2021 paper accepted ※ 27 May 2021 issue date ※ 16 August 2021

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TUPAB034

Development of Multi-Alkali Antimonides Photocathodes for High-Brightness RF Photoinjectors

electron, emittance, site, laser

1416

S.K. Mohanty, M. Krasilnikov, A. Oppelt, H.J. Qian, F. Stephan
DESY Zeuthen, Zeuthen, Germany
G. Guerini Rocco, C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
P. Michelato, L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy

Multi-alkali antimonide-based photocathodes are suitable candidate for the electron sources of next-generation high brightness RF photoinjectors due to their excellent photoemissive properties especially, like low thermal emittances and high sensitivity to visible light. The former stands out, paving the way towards CW operations. Based on the previous successful development of Cesium Telluride photocathodes, we are now channelling our efforts toward an R&D activity focused on KCsSb and NaKSb(Cs) photocathodes. Parallel to that R&D activity, we have installed a new dedicated photocathode production system at the INFN-LASA to start the preparation of these photocathodes for their test in the PITZ photoinjector at DESY in Zeuthen. In this paper, detailed experimental results obtained from the KCsSb, along with a preliminary result from the NaKSb(Cs) photocathode material as well as the status of the overall project are presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB034

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paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 02 September 2021

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TUPAB037

The Design of a High Charge Polarized Preinjector for the Electron-Ion Collider

gun, cavity, linac, electron

1428

E. Wang, W. Liu, V.H. Ranjbar, J. Skaritka, N. Tsoupas
BNL, Upton, New York, USA
J.M. Grames, J. Guo
JLab, Newport News, Virginia, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy
The design of the electron pre-injector of the Electron-Ion Collider (EIC) project to generate 4 x 7 nC bunch has been advancing to meet the requirements for injection into the Rapid Cycling Synchrotron (RCS). The major challenges are high charge transport and achieving small energy spread from 3 GHz traveling-wave plate(TWP). The designed preinjector includes the polarized electron source, bunching section, TWP Linac, zigzag phase space manipulation and spin rotator. In this report, we will discuss the RF frequency selection and the way to reduce energy spread down to 0.2% by longitudinal phase space manipulate. We will also report the results of beamline simulation using space charge code and the conceptual design of spin rotator.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB037

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paper received ※ 16 May 2021 paper accepted ※ 15 June 2021 issue date ※ 31 August 2021

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TUPAB105

Simulation Studies for Dark Current Signature From DLS RF Gun

simulation, electron, cavity, solenoid

1630

J. Karmakar, M. Aggarwal, S. Ghosh, B. Karmakar, P. Patra, B.K. Sahu, A. Sharma
IUAC, New Delhi, India

The Delhi Light source (DLS) is an upcoming compact THz facility at IUAC, New Delhi, based on pre-bunched FEL. RF conditioning of the 2.6 cell S-band RF gun is presently carried out with a Cu photo-cathode (PC) plug and dark current is produced when substantial accelerating field is reached inside the cavity. To identify the possible field emission sites contributing to dark current, single electron ASTRA simulations are done with a phase scan of the RF field. The simulation is extended to include multi-particle emission from the PC edge as a ring. The energies present in the dark current is analysed from the the Fowler Nordheim current plot and energy phase scan plot. The distribution of few dark current energies and their respective trajectories upto the YAG screen at a given solenoid setting is traced and shown in the simulations. We also present the dark current images captured during the initial RF conditioning and try to compare it with the simulations.

Poster TUPAB105 [0.742 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB105

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paper received ※ 19 May 2021 paper accepted ※ 17 August 2021 issue date ※ 28 August 2021

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TUPAB121

Photoinjector Drive Laser Temporal Shaping for Shanghai Soft X-Ray Free Electron Laser

laser, electron, FEL, flattop

1674

C.L. Li, X.T. Wang, W.Y. Zhang
Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
X.L. Dai
SSRF, Shanghai, People’s Republic of China
H.X. Deng, L. Feng, B. Liu, J.G. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China

Shanghai soft X ray free electron laser (SXFEL) initial designed shape of the photocathode driver laser is flattop produced by α-BBO stacking. The advantage of this design is attractive in producing electron bunch with low initial emittance and high uniformity along the electron bunch. However, some unavoidable modulations are generated along the laser pulse which trigger the electron bunch modulation generated at the source, which is due to the fast response time (tens of femtosecond) of copper cathode. In order to eliminate the modulation of electron bunch, temporal Gaussian driver laser was designed and tested, measurement results show the electron bunch longitudinal modulation was removed. In this paper, we present two kinds of driver laser pulse temporal shaping methods based on α-BBO stacking and UV grating pair shaping. Moreover, corresponding electron bunch temporal profile are also presented.

Poster TUPAB121 [2.469 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB121

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paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 10 August 2021

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TUPAB127

Spare Gun Multi-Physics Analysis for LCLS-II

gun, cavity, simulation, electron

1688

L. Xiao, C. Adolphsen, A. Cedillo, E.N. Jongewaard, X. Liu, C.-K. Ng, F. Zhou
SLAC, Menlo Park, California, USA

LBNL APEX VHF normal conducting gun was adopted for LCLS-II CW operation to provide ultra-bright high repetition rate X-ray pulses. The initial LCLS-II gun and injector commissioning showed excessive dark current dominated by field emission around the cathode plug outer diameter and the gun cavity nose. There is a concern that the dark current may get worse with time of operation. It is planning to build a spare rf gun largely based on the current LCLS-II gun to replace current LCLS-II gun. The proposed spare gun has a reduced the peak electrical fields around the cathode plug corner and cavity nose by 10% through further optimizing APEX gun cavity shape. In addition, there are some moderate modifications on the engineering design to increase mechanical robustness and vacuum performance. SLAC developed parallel finite-element electromagnetic code suite ACE3P is used to apply for the spare gun modeling including RF, thermal and structural analysis at static and transient states to ensure its successful operation in LCLS-II. In this paper, the spare gun multi-physics analysis is described.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB127

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paper received ※ 19 May 2021 paper accepted ※ 20 August 2021 issue date ※ 25 August 2021

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TUPAB200

Status of the Electron Lens for Space Charge Compensation in SIS18

electron, gun, solenoid, space-charge

1880

K. Schulte-Urlichs, S. Artikova, D. Ondreka, P.J. Spiller
GSI, Darmstadt, Germany
P. Apse-Apsitis, I. Steiks
Riga Technical University, Riga, Latvia
M. Droba, O. Meusel, H. Podlech, K.I. Thoma
IAP, Frankfurt am Main, Germany

At GSI a project has been initiated to investigate the option of space charge compensation (SCC) by use of an electron lens in order to overcome space charge (SC) limits in the synchrotrons SIS18 and SIS100 for the Facility for Antiproton and Ion Research (FAIR). The repeated crossing of resonance lines due to the synchrotron motion in bunched beams is considered one of the main drivers of SC induced beam loss in the synchrotrons. Electron lenses provide a compensation of ion beam SC by virtue of their negative charge interacting with the ions in the overlap region while a time-varying compensation can be achieved by the modulation of the electron beam. In order to demonstrate space charge compensation of bunched ion beams, an electron lens is under development for the application in SIS18. In this contribution, the status of the electron lens design will be reported putting special emphasis on its main components: the RF modulated electron gun, that is being developed within an ARIES collaboration, and the magnet system.

Poster TUPAB200 [1.869 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB200

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paper received ※ 19 May 2021 paper accepted ※ 23 June 2021 issue date ※ 17 August 2021

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TUPAB236

Progress on the Electron Gun Design for a McMillan Electron Lens in the Fermilab Integrable Optics Test Accelerator (IOTA)

electron, gun, simulation, optics

1988

B.L. Cathey, G. Stancari
Fermilab, Batavia, Illinois, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
This paper covers the progress made so far in designing the first McMillan electron lens for the Fermilab IOTA ring. The novel design allows for an increase in tune spread without limiting the dynamic aperture due to its integrability. Shown are simulations for an electron gun design to generate the specific required current density distribution for the nonlinear integrable system in IOTA.

Poster TUPAB236 [5.391 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB236

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

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TUPAB366

Design and Realization of New Solenoids for High Brightness Electron Beam Injectors

solenoid, gun, electron, simulation

2374

A. Vannozzi, D. Alesini, A. Giribono, C. Vaccarezza
INFN/LNF, Frascati (Roma), Italy

High-brightness, high-current electron beams are the main requirement for fourth generation light sources such as free-electron lasers (FELs), energy recovery Linacs (ERLs) and high-energy linear colliders. The most successful device for producing such beams is the Radio-Frequency photoinjector where a key element is the gun solenoid. Its main task is to limit the beam emittance growth in the first acceleration stages by imposing a spiraling motion to the beam. This paper is focused on two magnets: the first one is the solenoid gun for the new photoinjector at INFN-LNF SPARC_LAB test facility. The design, the realization, and all the measurements performed at the factory and at LNF are shown. Moreover, the design of a solenoid for a novel C-band gun for CompactLight project is presented. Both magnets have been designed with the goal to reach the same integrated field of the gun solenoid currently installed at SPARC_LAB, with an integrated field quality of 5·10^-4 in a good field radius of 30mm and 10mm radius respectively for SPARC_LAB and CompactLight solenoid. This one is equipped with a bucking coil to limit the field on cathode that could led to an undesired emittance growth.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB366

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paper received ※ 19 May 2021 paper accepted ※ 18 June 2021 issue date ※ 12 August 2021

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TUPAB396

The Thermal Outgassing Rate of Materials Used in Vacuum Systems

vacuum, experiment, diagnostics, radiation

2447

A.M. Semenov
BINP & NSTU, Novosibirsk, Russia
A. Burdakov, A.A. Krasnov, B.P. Tolochko, A.V. Varand
BINP SB RAS, Novosibirsk, Russia
S.R. Ivanova
GPI, Moscow, Russia
A.A. Krasnov
NSU, Novosibirsk, Russia
M.A. Mikhailenko
ISSCM SB RAS, Novosibirsk, Russia
A.A. Shoshin
Budker INP & NSU, Novosibirsk, Russia

There are many rarely used materials in vacuum systems that are poorly investigated in terms of vacuum properties. For example, phosphors, scintillating materials, ferrites, various adhesives, etc. In addition, new organic materials are being developed with mechanical properties similar to those of conventional steel. The use of such materials is very promising in vacuum technology. This article presents the thermal degassing performance of several rarely used materials and promising materials for vacuum applications.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB396

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paper received ※ 18 May 2021 paper accepted ※ 26 August 2021 issue date ※ 31 August 2021

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WEXA02

Operational Electron Cooling in the Relativistic Heavy Ion Collider

electron, operation, collider, cavity

2516

A.V. Fedotov, K.A. Drees, W. Fischer, X. Gu, D. Kayran, J. Kewisch, C. Liu, K. Mernick, M.G. Minty, V. Schoefer, H. Zhao
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.
Since the invention of the electron cooling technique its application to cool hadron beams in colliders was considered for numerous accelerator physics projects worldwide. However, achieving the required high-brightness electron beams of required quality and cooling of ion beams in collisions was deemed to be challenging. An electron cooling of ion beams employing a high-energy approach with RF-accelerated electron bunches was recently successfully implemented at BNL. It was used to cool ion beams in both collider rings with ion beams in collision. Electron cooling in RHIC became fully operational during the 2020 physics run and led to substantial improvements in luminosity. This presentation will discuss implementation, optimization and challenges of electron cooling for colliding ion beams in RHIC.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEXA02

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paper received ※ 18 May 2021 paper accepted ※ 15 June 2021 issue date ※ 13 August 2021

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WEXC03

Review of Superconducting Radio Frequency Gun

gun, SRF, cavity, operation

2556

R. Xiang
HZDR, Dresden, Germany

The success of proposed high power free-electron lasers (FELs) and energy recovery linac (ERL) largely depends on the development of the electron source, which requires the best beam quality and CW operation. An elegant way to realize this average brilliance is to combine the high beam quality of mature normal conducting radio frequency photoinjector with the quick developing superconducting radio frequency technology, to build superconducting rf photoinjectors (SRF guns). In last decade, several SRF gun programs based on different approaches have achieved promising progress, even succeeded in routine operation at BNL and HZDR [*,**]. In the near future SRF guns are expected to play an important role for hard X-ray FEL facilities. In this contribution, we will review the design concepts, parameters, and the status of the major SRF gun projects.
*I. Petrushina et al., Phys. Rev. Lett. 124, 244801
**J. Teichert at al., Phys. Rev. Accel. Beams 24, 033401

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEXC03

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paper received ※ 19 May 2021 paper accepted ※ 28 June 2021 issue date ※ 11 August 2021

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WEPAB040

Characterization of Low Emittance Electron Beams Generated by Transverse Laser Beam Shaping

laser, emittance, flattop, electron

2690

M. Groß, N. Aftab, P. Boonpornprasert, G.Z. Georgiev, J. Good, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, G. Shu, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany
Y. Chen, G. Loisch
DESY, Hamburg, Germany
I. Will
MBI, Berlin, Germany

Linac based X-ray free electron laser demand a high beam quality from the electron source, therefore RF photoinjectors are used to generate the electron bunches for state of the art beam brightness. One important figure of merit for these injectors is the transverse emittance of the generated electron beam, which can be minimized by shaping the photocathode laser pulses. Best performance can be achieved with ellipsoidal laser pulses, but 3D shaping is technically challenging. Typically, a quasi-uniform transverse laser profile is truncated from the Gaussian profile generated by the laser with an aperture to reduce the transverse nonlinear space charge forces. This is investigated in detail by optimizing the laser transverse profile at the Photoinjector Test facility at DESY in Zeuthen (PITZ), where photoinjector R&D is conducted for the E-XFEL and FLASH free electron lasers at DESY in Hamburg. In this contribution we present experimental results at high acceleration gradients (up to 60 MV/m) for both 250 pC and 500 pC. For a bunch charge of 500 pC an emittance reduction of about 30% compared to the commonly used transverse flat-top laser distribution was achieved.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB040

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paper received ※ 17 May 2021 paper accepted ※ 02 June 2021 issue date ※ 31 August 2021

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WEPAB051

Beam Dynamics for a High Field C-Band Hybrid Photoinjector

electron, emittance, linac, gun

2714

L. Faillace, F. Bosco, M. Carillo, L. Giuliano, M. Migliorati, A. Mostacci, L. Palumbo
Sapienza University of Rome, Rome, Italy
R.B. Agustsson, I.I. Gadjev, S.V. Kutsaev, A.Y. Murokh
RadiaBeam, Marina del Rey, California, USA
M. Behtouei, A. Giribono, B. Spataro, C. Vaccarezza
INFN/LNF, Frascati, Italy
A. Fukasawa, N. Majernik, J.B. Rosenzweig, O. Williams
UCLA, Los Angeles, California, USA
S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This work supported by DARPA GRIT under contract no. 20204571 and partially by INFN National Committee V through the ARYA project.
In this paper, we present a new class of a hybrid photoinjector in C-Band. This project is the effort result of a UCLA/Sapienza/INFN-LNF/SLAC/RadiaBeam collaboration. This device is an integrated structure consisting of an initial standing-wave 2.5-cell gun connected to a traveling-wave section at the input coupler. Such a scheme nearly avoids power reflection back to the klystron, removing the need for a high-power circulator. It also introduces strong velocity bunching due to a 90° phase shift in the accelerating field. A relatively high cathode electric field of 120 MV/m produces a ~4 MeV beam with ~20 MW input RF power in a small foot-print. The beam transverse dynamics are controlled with a ~0.27 T focusing solenoid. We show the simulation results of the RF/magnetic design and the optimized beam dynamics that shows 6D phase space compensation at 250 pC. Proper beam shaping at the cathode yields a ~0.5 mm-mrad transverse emittance. A beam waist occurs simultaneously with a longitudinal focus of <400 fs rms and peak current >600 A. We discuss application of this injector to an Inverse-Compton Scattering system and present corresponding start-to-end beam dynamics simulations.

Poster WEPAB051 [0.827 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB051

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paper received ※ 18 May 2021 paper accepted ※ 01 July 2021 issue date ※ 22 August 2021

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WEPAB092

Redesign of the Jefferson Lab -300 kV DC Photo-Gun for High Bunch Charge Operations

gun, high-voltage, simulation, electron

2802

S.A.K. Wijethunga, J.R. Delayen, G.A. Krafft, G.G. Palacios Serrano
ODU, Norfolk, Virginia, USA
J.F. Benesch, J.R. Delayen, C. Hernandez-Garcia, G.A. Krafft, M.A. Mamun, M. Poelker, R. Suleiman
JLab, Newport News, Virginia, USA

Funding: The U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177, JSA initiatives fund program and Laboratory Directed Research and Development program.
Production of high bunch charge beams for the Electron-Ion Collider (EIC) is a challenging task. High bunch charge (a few nC) electron beam studies at Jefferson Lab using an inverted insulator DC high voltage photo-gun showed evidence of space charge limitations starting at 0.3 nC, limiting the maximum delivered bunch charge to 0.7 nC for beam at -225 kV, 75 ps (FWHM) pulse width, and 1.64 mm (rms) laser spot size. The low extracted charge is due to the modest longitudinal electric field (Ez) at the photocathode leading to beam loss at the anode and downstream beam pipe. To reach the few nC high bunch charge goal, and to correct the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun the existing photo-gun was modified. This contribution discusses the electrostatic design of the modified photo-gun obtained using CST Studio Suite’s electromagnetic field solver. Beam dynamics simulations performed using General Particle Tracer (GPT) with the resulting electrostatic field map obtained from the modified electrodes confirmed the validity of the new design.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB092

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paper received ※ 20 May 2021 paper accepted ※ 02 June 2021 issue date ※ 19 August 2021

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WEPAB093

Space Charge Effects in Low Energy Magnetized Electron Beam

laser, electron, solenoid, space-charge

2806

S.A.K. Wijethunga, J.R. Delayen, G.A. Krafft
ODU, Norfolk, Virginia, USA
J.F. Benesch, G.A. Krafft, M.A. Mamun, M. Poelker, R. Suleiman, S. Zhang
JLab, Newport News, Virginia, USA

Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and Laboratory Directed Research and Development program.
Magnetized electron cooling is one of the major approaches towards obtaining the required high luminosity in the proposed Electron-Ion Collider (EIC). In order to increase the cooling efficiency, a bunched electron beam with a high bunch charge and high repetition rate is required. At Jefferson Lab, we generated magnetized electron beams with high bunch charge using a new compact DC high voltage photogun biased at -300 kV with bialkali-antimonide photocathode and a commercial ultra-fast laser. This contribution discusses how magnetization affects space charge dominated beams as a function of magnetic field strength, gun high voltage, and laser pulse width, and spot size in comparison with simulations performed using General Particle Tracer.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB093

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paper received ※ 19 May 2021 paper accepted ※ 08 June 2021 issue date ※ 23 August 2021

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WEPAB096

RF Testbed for Cryogenic Photoemission Studies

cryogenics, gun, electron, brightness

2810

G.E. Lawler, A. Fukasawa, N. Majernik, J.B. Rosenzweig, A. Suraj, M. Yadav
UCLA, Los Angeles, California, USA
Z. Li
SLAC, Menlo Park, California, USA
M. Yadav
The University of Liverpool, Liverpool, United Kingdom
M. Yadav
Cockcroft Institute, Warrington, Cheshire, United Kingdom

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 40K, 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.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB096

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paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 21 August 2021

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WEPAB097

Initial Nanoblade-Enhanced Laser-Induced Cathode Emission Measurements

electron, laser, simulation, experiment

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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WEPAB098

Cryogenic Component and Material Testing for Compact Electron Beamlines

cryogenics, cavity, electron, gun

2818

G.E. Lawler, N. Majernik, J.B. Rosenzweig
UCLA, Los Angeles, California, USA

Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE Contract DE-SC0020409
Cryogenic regimes of operation are, for various reasons, highly advantageous for normal conducting accelerator structures. Liquid cryogen-based systems are costly to implement and maintain. As a result, developing cryogenic test facilities at a smaller more cost effective scale using cryo-coolers is attractive. Before real implementations of a cryo-cooler based beamline, a significant amount of information is necessary regarding the behavior and properties of various components and materials at cryogenic temperatures. Finding this information lacking for our particular beamline case and by extension similar electron beamlines, we endeavor to generate a thorough beamline-relevant material and component properties down to the range of a liquid nitrogen temperatures (77 K) and the nominal operating temperature of a modest Gifford-McMahon cryocooler (45 K).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB098

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paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 18 August 2021

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WEPAB099

Near-Threshold Nonlinear Photoemission From Cu(100)

electron, laser, experiment, photon

2822

C.J. Knill, S.S. Karkare
Arizona State University, Tempe, USA
H.A. Padmore
LBNL, Berkeley, California, USA

Funding: National Science Foundation Grant No. PHY-1549132
Photocathodes that have a low mean transverse energy (MTE) are crucial to the development of compact X-ray Free Electron Lasers (XFEL) and ultrafast electron diffraction (UED) experiments. For FELs, low MTE cathodes result in a lower requirement for electron energy when lasing at a defined energy, and for a defined electron energy result in lasing at higher energy. For UED experiments, low MTE cathodes give a longer coherence length, allowing measurements on larger unit cell materials. A record low MTE of 5 meV has been recently demonstrated from a Cu (100) surface when measured near the photoemission threshold and cooled down to 30 K with liquid Helium [*]. For UED and XFEL applications that require a high charge density, the low quantum efficiency of Cu (100) near threshold necessitates the use of a high laser fluence to achieve the desired charge density [**]. At high laser fluences the MTE is limited by nonlinear effects, and therefore it is necessary to investigate near photoemission threshold at these high laser fluences. In this paper we report on nonlinear, near-threshold photoemission from a Cu (100) cathode, and its effect on the MTE.
* S. Karkare et al, Phys. Rev. Lett. 125, 054801 (2020)
** J. Bae et al, J. Appl. Phys., 124, 244903 (2018)

Poster WEPAB099 [0.829 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB099

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paper received ※ 19 May 2021 paper accepted ※ 21 July 2021 issue date ※ 20 August 2021

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WEPAB100

Heat Dissipation of Photocathodes at High Laser Intensities for a New DC Electron Source

electron, experiment, laser, operation

2826

M.A. Dehn, K. Aulenbacher
IKP, Mainz, Germany
K. Aulenbacher
HIM, Mainz, Germany
K. Aulenbacher
GSI, Darmstadt, Germany

Funding: This project was supported by the German science ministry BMBF through the Verbundforschung
Laser intensities of 1W or more are required to extract average beam currents of more than 10mA from photocathodes. Most of this laser power is converted into thermal load within the cathode and has to be dissipated to avoid excessive heating of the cathode and thus a significant reduction in lifetime. At Johannes Gutenberg-University Mainz, we are developing a new high current DC electron source operating at an energy of 100keV, where an efficient heat dissipation of the photocathode is achieved by a mechanical design of the supporting structure.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB100

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

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WEPAB101

An Improved Model for Photoemission of Space Charge Dominated Picosecond Electron Bunches: Theory and Experiment

electron, experiment, laser, space-charge

2829

S.M. Polozov, V.I. Rashchikov
MEPhI, Moscow, Russia
M. Krasilnikov
DESY Zeuthen, Zeuthen, Germany

The emission of a short highly charged electron bunch in a radiofrequency photogun is discussed. The traditional space charge limited emission numerical model is extended by an introduction of positively charged ions arising in the cathode region and dynamically changing during the emission. Estimates on the time characteristics of the charge migrating process in the semiconductor region are given. The numerical results are compared with the results of other numerical models and with experimental observations at the Photo Injector Test facility at DESY in Zeuthen (PITZ).

Poster WEPAB101 [1.601 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB101

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paper received ※ 08 May 2021 paper accepted ※ 07 June 2021 issue date ※ 29 August 2021

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WEPAB102

Half-Metal Spin Filter for Highly Polarized Emission from GaAs Photocathodes

electron, polarization, lattice, hardware

2833

S. Poddar, C.-J. Jing, E.J. Montgomery
Euclid Beamlabs, Bolingbrook, USA
P. Lukashev
University of Northern Iowa, Cedar Falls, Iowa, USA
C. Palmstrøm
UCSB, Santa Barbara, California, USA
M.L. Stutzman, S. Zhang
JLab, Newport News, Virginia, USA

Funding: Work supported by Department of Energy grant number DE-SC0020564.
GaAs-based photocathodes are one of the major sources of spin-polarized electrons and are crucial for the upcoming Electron-Ion collider experiments which includes study of proton spin and spin parity violation in the standard model. The theoretical polarization limit in unstrained GaAs photocathodes is 50 % but only 35 % is routinely achieved in experiments. Spin selective filtering allows to boost the spin polarization beyond the 50 % theoretical limit. In this work, first-principle electronic calculations using standard Density Functional Theory are performed to predict possible Heusler alloy half-metal candidates to be used as spin-filter. Simulations are also performed to investigate the half-metallicity as function of the magnetic spin direction. Several devices are experimentally fabricated using dedicated Molecular Beam Epitaxy growth system. We implemented Quantum Efficiency and Polarization testing of these half-metal/GaAs heterostructures using a dedicated Mott polarimeter system. Photoemission can also be seen on magnetically switching the spin-filter direction accompanied by a change in sign of the asymmetry which is a qualitative proof of the spin-filtering effect.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB102

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paper received ※ 20 May 2021 paper accepted ※ 28 July 2021 issue date ※ 18 August 2021

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WEPAB103

Systematic Beam Parameter Studies at the Injector Section of FLUTE

laser, emittance, electron, quadrupole

2837

T. Schmelzer, E. Bründermann, D. Hoffmann, I. Križnar, S. Marsching, A.-S. Müller, M.J. Nasse, R. Ruprecht, J. Schäfer, M. Schuh, N.J. Smale, P. Wesolowski, T. Windbichler
KIT, Karlsruhe, Germany

Funding: This work is supported by the DFG-funded Doctoral School "Karlsruhe School of Elementary and Astroparticle Physics: Science and Technology (KSETA)"
FLUTE (Ferninfrarot Linac- und Test-Experiment) is a compact linac-based test facility for accelerator R&D and source of intense THz radiation for photon science. In preparation for the next experiments, the electron beam of the injector section of FLUTE has been characterized. In systematic studies the electron beam parameters, e.g., beam energy and emittance, are measured with several diagnostic systems. This knowledge allows the establishment of different operation settings and the optimization of electron beam parameters for future experiments.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB103

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paper received ※ 19 May 2021 paper accepted ※ 26 August 2021 issue date ※ 01 September 2021

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WEPAB104

Improving the Operational Lifetime of the CEBAF Photo-Gun by Anode Biasing

laser, simulation, electron, gun

2840

J.T. Yoskowitz, G.A. Krafft, G.G. Palacios Serrano, S.A.K. Wijethunga
ODU, Norfolk, Virginia, USA
J.M. Grames, J. Hansknecht, C. Hernandez-Garcia, M. Poelker, M.L. Stutzman, R. Suleiman
JLab, Newport News, Virginia, USA
S.B. van der Geer
Pulsar Physics, Eindhoven, The Netherlands

Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
The operating lifetime of GaAs-based photocathodes in DC high voltage electron photo-guns is dominated by the ionization rate of residual beamline gas molecules. In this work, experiments were performed to quantify the improvement in photocathode charge lifetime by biasing the photo-gun anode with a positive voltage, which repels ions generated downstream of the anode. The photo-cathode charge lifetime improved by almost a factor of two when the anode was biased compared to the usual grounded configuration. Simulations were performed using the particle tracking code General Particle Tracer (GPT) with a new custom element. The simulation results showed that both the number and energy of ions play a role in the pattern of QE degradation. The experiment results and conclusions supported by GPT simulations will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB104

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paper received ※ 20 May 2021 paper accepted ※ 02 June 2021 issue date ※ 24 August 2021

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WEPAB105

Simulating Electron Impact Ionization Using a General Particle Tracer (GPT) Custom Element

electron, simulation, gun, high-voltage

2843

J.T. Yoskowitz, G.A. Krafft
ODU, Norfolk, Virginia, USA
J.M. Grames
JLab, Newport News, Virginia, USA
G.R. Montoya Soto
Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico
C.A. Valerio
ECFM-UAS, Culiacan, Sinaloa, Mexico
S.B. van der Geer
Pulsar Physics, Eindhoven, The Netherlands

Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177, Consejo Nacional de Ciencia y Tecnología (CONACYT).
A new C++ custom element has been developed with the framework of General Particle Tracer (GPT) to simulate electron impact ionization of residual gas molecules. The custom element uses Monte-Carlo routines to determine both the ion production rate and the secondary electron kinetic energy based on user-defined gas densities and theoretical values for the ionization cross section and the secondary electron differential cross section. It then uses relativistic kinematics to track the secondary electron, the scattered electron, and the newly formed ion after ionization. The ion production rate and the secondary electron energy distribution determined by the custom element have been benchmarked against theoretical calculations and against simulations made using the simulation package IBSimu. While the custom element was originally built for particle accelerator simulations, it is readily extensible to other applications. The custom element will be described in detail and examples of applications at the Thomas Jefferson National Accelerator Facility will be presented for ion production in a DC high voltage photo-gun.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB105

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paper received ※ 20 May 2021 paper accepted ※ 25 June 2021 issue date ※ 02 September 2021

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WEPAB106

Study on Durability Improvement of Cs-Te Photocathode by Means of Alkali Halide Protective Films

electron, experiment, ECR, laser

2847

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

We have been conducting basic and applied research for generating high quality electron beams, using 1.6 cell laser photocathode RF-gun. In our laboratory, Cesium Telluride (Cs-Te), one of the semiconductor photocathodes, is used as an electron source for accelerator experiments. This semiconductor photocathode is known for high quantum efficiency (Q.E.) about 5~10% and 3-month 1/e lifetime. High Q.E. photocathodes can reduce the power requirement of the laser system, and long lifetime photocathodes can decrease the maintenance frequency, contributing to an efficient experimental environment. For these reasons, high Q.E. and long lifetime photocathodes are necessary in accelerator experiments. In order to produce robust photocathodes and extend the lifetime, we have conducted covering Cs-Te photocathodes with CsBr and CsI protective films. In this conference, we report the thickness dependency on the lifetime of Cs-Te photocathodes when we intentionally exposed oxygen gas to coated and non-coated Cs-Te photocathodes.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB106

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paper received ※ 19 May 2021 paper accepted ※ 02 June 2021 issue date ※ 01 September 2021

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WEPAB109

Initial Study of GaN Thin Films for Photocathodes Prepared by Magnetron Sputtering on Copper Substrates

electron, plasma, gun, experiment

2850

M. Vogel, X. Jiang, C. Wang
University Siegen, Siegen, Germany
P. Murcek, J. Schaber, R. Xiang
HZDR, Dresden, Germany

Funding: This research is funded by the Federal Ministry of Education and Research of Germany in the framework of BETH (project number 05K19PSB).
On the path for high brightness electron beams, Gallium Nitride (GaN) is one promising candidate for a photo-cathode material. In this contribution, we report on the continuation of the study to optimize the crystallization quality and crystallography of Mg-doped GaN samples on copper substrates that are synthesized by RF magnetron sputtering. SEM and XRD results show that the pretreatment methods and the sputtering conditions (temperature, sputtering power, and partial pressure of the reactive gas) can both affect the morphology and crystal quality of GaN films. The initial QE measurements of these samples are done in our newly build in-situ QE measurement system and the first results of QE analyses done at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) are presented in a dedicated contribution.
Part of this work was performed at the Micro- and Nanoanalytics Facility (MNaF) of the University of Siegen.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB109

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paper received ※ 19 May 2021 paper accepted ※ 09 June 2021 issue date ※ 29 August 2021

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WEPAB111

Controlled Degradation by Oxygen Exposure in the Performance of a Ag (100) Single-Crystal Photocathode

experiment, electron, cryogenics, emittance

2856

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

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 including the work function, intrinsic emittance, and quantum efficiency of the photocathode. These factors in turn define the electron beam performance which is measurable as normalized 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 electron source community**. As such, pure metal photocathodes and their performance at UV wavelengths are of interest as seen at the LCLS at SLAC and CLARA at Daresbury. We present performance data for an Ag (100) single-crystal photocathode under illumination at 266 nm wavelength, with known levels of surface roughness, using our Transverse Energy Spread Spectrometer (TESS)*** both at room and cryogenic temperatures. Crucially our data shows the effect of progressive degradation in the photo-cathode performance as a consequence of exposure to controlled levels of oxygen.
* D.H. Dowell, et al., Nucl. Instr. and Meth. A (2010), doi:10.1016/j.nima.2010.03.104
** Appl. Phys. Lett. 89, 224103 (2006); doi:10.1063/1.2387968
*** Proc. FEL’13, TUPPS033, 290-293

Poster WEPAB111 [0.866 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB111

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paper received ※ 20 May 2021 paper accepted ※ 22 June 2021 issue date ※ 21 August 2021

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WEPAB112

Performance Characterisation of a Cu (100) Single-Crystal Photocathode

electron, emittance, experiment, photon

2860

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

The search for high performance photocathode electron sources is a priority in the accelerator science community. The surface characteristics of a photocathode define important factors of the photoemission including the intrinsic emittance, the quantum efficiency and the work function of the photocathode. These factors in turn define the electron beam performance which are measurable as emittance, brightness and energy spread. We have used ASTeC’s Multiprobe (SAPI)* to characterise and analyse photocathode performance using multiple techniques including XPS, STM, and LEED imaging, and their Transverse Energy Spread Spectrometer (TESS)** to measure mean transverse energy (MTE). We present characterisation measurements for a Cu (100) single-crystal photocathode sample with data from SAPI confirming the crystallographic face and showing surface composition and roughness, supported by data from TESS showing the photocathode electron beam energy spread.
* B.L. Militsyn, 4-th EuCARD2 WP12.5 meeting, Warsaw, 14-15 March 2017
**Proc. FEL’13, TUPPS033, 290-293

Poster WEPAB112 [0.814 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB112

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paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 25 August 2021

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WEPAB115

Beam Preparation with Temporally Modulated Photocathode Laser Pulses for a Seeded THz FEL

FEL, laser, electron, simulation

2866

G.Z. Georgiev, N. Aftab, P. Boonpornprasert, J. Good, M. Groß, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, A. Lueangaramwong, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany
N. Chaisueb
Chiang Mai University, Chiang Mai, Thailand
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

The need for carrier-envelope-phase (CEP) stable THz pump pulses is recognized at many pump-probe experiments at the European XFEL. At the Photo Injector Test Facility at DESY in Zeuthen (PITZ), a proof-of-principle experiment of an accelerator-based THz FEL source is in preparation. Since the CEP stability of FEL pulses is not guaranteed in the SASE regime, a seeding scheme is needed. A common scheme for seeding is to drive the microbunching process with external laser pulses, which are power-limited in the THz range. Alternatively, a pre-bunched beam, generated for example by applying a temporally modulated photocathode laser pulse, can be used to drive the FEL. The beam dynamics with such a seeding method are studied with ASTRA tracking code simulations with space-charge forces as well as experimentally. The results of these studies are shown and discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB115

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paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 21 August 2021

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WEPAB138

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

gun, SRF, electron, cavity

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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WEPAB149

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

cavity, gun, electron, linac

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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WEPAB157

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

electron, brightness, lattice, scattering

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

electron, gun, injection, acceleration

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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WEPAB169

Towards Ultra-Smooth Alkali Antimonide Photocathode Epitaxy

lattice, interface, emittance, electron

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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WEPAB256

Three-Dimensional Space Charge Oscillations in a Hybrid Photoinjector

emittance, plasma, simulation, electron

3240

M. Carillo, M. Behtouei, F. Bosco, L. Faillace, A. Giribono, L. Giuliano, M. Migliorati, A. Mostacci, L. Palumbo
Sapienza University of Rome, Rome, Italy
L. Ficcadenti
INFN-Roma, Roma, Italy
J.B. Rosenzweig
UCLA, Los Angeles, California, USA
B. Spataro, C. Vaccarezza
INFN/LNF, Frascati, Italy

Funding: This work supported by DARPA GRIT under contract no. 20204571 and partially by INFN National committee V through the ARYA project.
A new hybrid C-band photo-injector, consisting of a standing wave RF gun connected to a traveling wave structure, operating in a velocity bunching regime, has shown to produce an extremely high brightness beam with very low emittance and a very high peak current through a simultaneous compression of the beam in the longitudinal and transverse dimensions. A beam slice analysis has been performed in order to understand the evolution of the relevant physical parameters of the beam in the longitudinal and transverse phase spaces along the structure. A simple model for the envelope equation has been developed to describe the beam behavior in this particular dynamics regime that we term "triple waist", since all three dimensions reach a minimum condition almost simultaneously. The model analyzes the transverse envelope dynamics at the exit of the hybrid photo-injector, in the downstream drift where the triple waist occurs. The analytical solutions obtained from the envelope equation are compared with the simulations, showing a good agreement. Finally, these results have been analyzed also in terms of plasma oscillation to obtain a further physical interpretation of the beam dynamics.

Poster WEPAB256 [1.162 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB256

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paper received ※ 19 May 2021 paper accepted ※ 21 July 2021 issue date ※ 12 August 2021

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WEPAB290

Pointing Stabilization Algorithms Explored and Implemented with the Low Energy RHIC Electron Cooling Laser

laser, operation, electron, feedback

3336

L.K. Nguyen
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 electron beam for the Low Energy RHIC electron Cooler (LEReC) at Brookhaven National Laboratory (BNL) is generated by a high-power fiber laser illuminating a photocathode, with a total propagation distance of 34 m separating the laser output and the photocathode. This propagation is facilitated by three independent laser tables that have varying responses to changes in time of day, weather, and season. Alignment drifts induced by these environmental changes are mitigated by an active "slow" pointing stabilization system found along the length of the transport, and this in-house system was commissioned as part of the full laser transport in 2019, as previously reported*. In 2020, the system became fully operational alongside LEReC, the world’s first electron cooler in a collider, and helped establish the transverse stability of the electron beam required for cooling. A summary of the different slow stabilization algorithms, which were continually refined during the run in order to achieve long-term center-of-mass stability of the laser spot on the photocathode to within 10 microns RMS, is provided.
* L. K. Nguyen et al., "Active Pointing Stabilization Techniques Applied to the Low Energy RHIC Electron Cooling Laser Transport at BNL", presented at NAPAC’19, paper THYBA6.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB290

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paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 30 August 2021

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WEPAB296

A Klystron Phase Lock Loop for RF System at TPS Booster Ring

controls, klystron, LLRF, injection

3354

F.Y. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.D. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh, T.-C. Yu
NSRRC, Hsinchu, Taiwan

In TPS booster ring, the DLLRF is used to controlled the ramping gap voltage and also the energy saving module is applied to save power while the ring does not inject beam. But we occurred to have a problem of PI saturation due to a large phase change when the energy saving module working. The energy saving module switches the anode voltage of the klystron from high to low level to decrease the cathode current while the ring does not inject and do the opposite while the ring injects. This action causes a large phase change of the transmitter and leads the PI controller to work in the wrong direction. We add a klystron phase loop to solve this situation.

Poster WEPAB296 [0.792 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB296

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paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 31 August 2021

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WEPAB308

Measurement-Based Surrogate Model of the SLAC LCLS-II Injector

laser, simulation, network, controls

3395

L. Gupta, Y.K. Kim
University of Chicago, Chicago, Illinois, USA
A.L. Edelen, C.E. Mayes, A.A. Mishra, N.R. Neveu
SLAC, Menlo Park, California, USA

Funding: This project was funded by the DOE SCGSR Program.
There is significant effort within particle accelerator physics to use machine learning methods to improve modeling of accelerator components. Such models can be made realistic and representative of machine components by training them with measured data. These models could be used as virtual diagnostics or for model-based control when fast feedback is needed for tuning to different user settings. To prototype such a model, we demonstrate how a machine learning based surrogate model of the SLAC LCLS-II photocathode injector was developed. To create machine-based data, laser measurements were taken at the LCLS using the virtual cathode camera. These measurements were used to sample particles, resulting in realistic electron bunches, which were then propagated through the injector via the Astra space charge simulation. By doing this, the model is not only able to predict many bulk electron beam parameters and distributions which are often hard to measure or not usually available to measure, but the predictions are more realistic relative to traditionally simulated training data. The methods for training such models, as well as model capabilities and future work are presented here.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB308

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paper received ※ 26 May 2021 paper accepted ※ 27 July 2021 issue date ※ 21 August 2021

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WEPAB327

Sheet Electron Probe for Beam Tomography

electron, proton, diagnostics, simulation

3437

V.G. Dudnikov, M.A. Cummings, G. Dudnikova
Muons, Inc, Illinois, USA

Funding: Work is funded by DOE SBIR grant DE-SC0021581
An electron beam probe has been successfully used for the determination of accelerated particle density distributions. However, the apparatus used for this diagnostic had a large size and complex design which limit the broad use of this diagnostic for tomography of accelerated bunches. We propose a new approach to electron beam tomography: we will generate a continuous sheet of electrons. As the ion beam bunches pass through the sheet, they cause distortions in the distribution of sheet electrons arriving at CCD device on the other side of the beam that is interpreted to give a continuous measurement of the beam profile. The apparatus to generate the sheet beam is a strip cathode, which, compared to the scanning electron beam probe, is smaller, has a simpler design and less expensive manufacturing, has better magnetic shielding, has higher sensitivity, higher resolution, has better accuracy of measurement and better time resolution. With this device, it is possible to develop almost ideal tomography diagnostics of bunches in linear accelerators and in circular accelerators and storage rings.

Poster WEPAB327 [0.640 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB327

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paper received ※ 19 May 2021 paper accepted ※ 15 July 2021 issue date ※ 25 August 2021

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WEPAB328

Rapid Surface Microanalysis Using a Low Temperature Plasma

plasma, electron, radiation, target

3440

V.G. Dudnikov, M.A. Cummings, R.P. Johnson
Muons, Inc, Illinois, USA

There is a need for rapid, high-resolution (micron or sub-micron) scanning of surfaces of special nuclear materials (SNM) and surrogate materials to locate and identify regions of abnormalities. One technique that is commonly used to analyze the composition of solid surfaces and thin films is secondary-ion mass spectrometry (SIMS). SIMS devices are very complex and expensive. We propose to develop simpler, less expensive surface analysis devices, based on glow-discharge optical emission spectroscopy (GOES) that can provide excellent spatial resolution. Ions from a plasma discharge sputtered atoms from the surface and the discharge electrons effectively excite and ionize the sputtered atoms. GOES uses the light emitted by the excited particles for quantitative analysis. In the GOES device, the ion flux is extracted from the gas-discharge plasma and focused to a micron size on the sample, providing very local sputtering and local elemental analysis. The radiation from the sputtered atoms is passed through an optical fiber to an optical spectrometer and recorded. To register the distribution of elements over the sample, the sample is scanned electro-mechanically.

Poster WEPAB328 [0.385 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB328

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paper received ※ 19 May 2021 paper accepted ※ 29 July 2021 issue date ※ 24 August 2021

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WEPAB336

Aluminum Vacuum Chamber for the Sirius Commissioning Undulators

undulator, vacuum, MMI, storage-ring

3467

B.M. Ramos, O.R. Bagnato, R.O. Ferraz, H.G. Filho, P.P.S. Freitas, G.R. Gomes, P.H. Lima, R.F. Oliveira, T.M. Rocha, F. Rodrigues, R.M. Seraphim, D.R. Silva, M.B. Silva
LNLS, Campinas, Brazil

Sirius is a 3 GeV fourth generation light source under commissioning by the Brazilian Synchrotron Light Laboratory (LNLS). Compact Linear Polarizing Undulators with magnet vertical aperture of 8 mm have been used for the commissioning of some beam lines. Extruded aluminum vacuum chambers having small vertical aperture of 6 mm and horizontal aperture of 40 mm, were built. This paper details the design and manufacturing processes of a complete chamber and its installation procedure at the storage ring. Challenges regarding the precision machining of the 0.5 mm wall thickness, TIG welding for aluminum, NEG coating for small apertures will also be presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB336

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

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WEPAB379

Photocathode Laser Development for Superconducting X-Ray Free Electron Lasers at DESY

laser, FEL, operation, electron

3599

C. Li, O. Akcaalan, U. Grosse-Wortmann, I. Hartl, C. Mohr, M. Seidel, H. Tuennermann, C. Vidoli, L. Winkelmann
DESY, Hamburg, Germany
M. Frede, O. Puncken
neoLASE GmbH, Hanover, Germany

Funding: Deutsches Elektronen-Synchrotron, Hamburg, 22609, Germany
Modern X-Ray Free-Electron Lasers (XFEL) are a key tool to enable a variety of scientific research. Those large-scale machines rely on robust and reliable deep ultraviolet (DUV) laser sources to drive electrons from their RF photocathode gun. In this paper we present a new photocathode laser prototype, which offers more flexibility in duration and shape of the 257.5 nm pulses for driving the CsTe Photocathodes of DESY’s superconducting burst-mode FELs. The laser matches the FEL pulse structure, which are 800 µs bursts at up to 4.5 MHz intraburst-rate with 10 Hz burst-repetition-rate. In a first version the system will offer variable DUV pulse durations, tunable from 1 ps to 20 ps to address different operational regimes of the XFEL. The laser system comprises a high-resolution spectral shaper with the option of generating flat-top DUV pulses for reducing electron-beam emittance at a later version. The laser is constructed in a hybrid Yb:fiber and Yb:YAG architecture. Our prototype delivers 180 uJ pulse energy at 1030 nm and 1 MHz intra-burst rate and we demonstrated conversion of 50µJ of the NIR beam to DUV, resulting 11.5µJ at 21ps (FWHM) and 6.15 µJ at 1.05 ps (FWHM) pulse duration.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB379

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paper received ※ 27 May 2021 paper accepted ※ 02 July 2021 issue date ※ 29 August 2021

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WEPAB385

Beam Dynamic Analysis of RF Modulated Electron Beam Produced by Gridded Thermionic Guns

electron, gun, emittance, linac

3618

G. Adam
University of Strathclyde, Glasgow, United Kingdom
A.W. Cross, L. Zhang
USTRAT/SUPA, Glasgow, United Kingdom
B.L. Militsyn
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
B.L. Militsyn
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Funding: Science and Technology Facilities Council (STFC) U.K training grant, industrial case with TMD Ltd, UK ST/R002141/1 "Accelerators for Security, healthcare and Environmental applications ".
A thermionic cathode gridded electron gun used in injectors for different types of circular and linear particle accelerators and for energy recovery configurations was studied. Both theory and numerical simulation were used to explore the relationship between the bunch charge and bunch length. The electron gun is based on a Pierce-type geometry. It was initially designed using Vaughan synthesis followed by optimization using a 2D electron trajectory solver TRAK. After optimization, the grid in front of the cathode was inserted and the RF field was introduced through a coaxial waveguide structure. The complete gun was simulated using the PIC code MAGIC. High duty cycle operations at frequencies 1.5 GHz and 3.0 GHz, were investigated using different combinations of both the bias and the RF voltage applied between the cathode and the grid. The beam dynamics results from the PIC showed that a minimum bunch length of 10⁶ ps could be achieved with a bunch charge of 33 pC when the driving RF frequency was 1.5 GHz. Operating at the higher RF frequency of 3GHz did not significantly reduce the bunch length. The normalized emittance of about 5.6 mm-mrad was demonstrated in PIC simulations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB385

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paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 24 August 2021

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THXC07

Adaptive Control of Klystron Operation Parameters for Energy Saving at Storage Ring of TPS

klystron, operation, controls, storage-ring

3748

T.-C. Yu, F.Y. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.D. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh
NSRRC, Hsinchu, Taiwan

To satisfy maximum beam current operation in the storage ring of TPS, the operation parameters of both RF transmitters are set to be able to generate its maxi-mum RF power in daily usage. Under such condition, the klystrons can deliver any power below 300kW at constant AC power consumption which is about 520-530 kW. Hence, the AC power usage is independent of the required RF output power. To best utilize the avail-able AC power based on the required RF power, an adaptive control methodology is proposed here to change the operation parameters of the klystron, cath-ode voltage and anode voltage, according to the pre-sent RF power. The corresponding operation parame-ters are applied by the prior tested table which maps the operation parameters with the different saturation RF power. The test results show that the saved energy can be 32% to 11% from 30mA to 450mA for both RF plants as comparing to constant operation parameters of 1047 kW AC power.

Slides THXC07 [1.241 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXC07

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paper received ※ 19 May 2021 paper accepted ※ 06 July 2021 issue date ※ 29 August 2021

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THPAB022

Possibilities for Upgrading to Polarized SuperKEKB

electron, polarization, experiment, lattice

3799

Z.J. Liptak, M. Kuriki
HU/AdSM, Higashi-Hiroshima, Japan
J.M. Roney
Victoria University, Victoria, B.C., Canada

The SuperKEKB accelerator is currently in operation in Tsukuba, Japan, with a planned long shutdown in 2026. Among the possible upgrades being considered during this period is the change to a polarized electron beam in the High Energy Ring. Such a change would require modifications in the source generation and transport, geometrical and lattice variations to provide spin rotation, and polarimetry. A Polarized SuperKEKB Working Group has been formed from members of the Belle II experiment and the SuperKEKB accelerator team to investigate the possibilities and challenges of these modifications. This talk lays out the goals of the proposed upgrade, considers the necessary changes to the existing accelerator and their feasibility and lays out the physics motivation behind such an effort.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB022

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paper received ※ 19 May 2021 paper accepted ※ 23 July 2021 issue date ※ 15 August 2021

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THPAB082

Recent Operational Experience with Thermionic RF Guns at the APS

gun, linac, operation, injection

3959

Y. Sun, M. Borland, G.I. Fystro, X. Huang, H. Shang
ANL, Lemont, Illinois, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
The electron beam at the Argonne Advanced Photon Source (APS) is generated from an S-band thermionic RF gun. There are two locations at the frontend of the linac where thermionic RF guns are installed – RG1 and RG2. Three so-called generation-III guns are available, two are installed at RG1 and RG2, one is a spare. In recent years, these guns are showing signs of aging after over a couple of decades of operations. RF trips started to occur, and we had to reduce the nominal operating rf power to alleviate the problem. In addition, beam generated by RG1 suffers from low transportation efficiency from the gun to the linac, and beam trajectory is unstable which results in charge instabilities. Recently, APS obtained a new type of prototype gun and it was beam commissioned in the linac. In this paper, we report our operational experience with these thermionic rf guns including thermionic-cathode beam extraction, gun front-end optimization for maximum charge transmission through the linac, linac lattice setup to match beam for injection into the Particle Accumulator Ring (PAR) and optimization for maximum PAR injection efficiency.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB082

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paper received ※ 19 May 2021 paper accepted ※ 28 July 2021 issue date ※ 16 August 2021

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THPAB129

Beam Dynamics Simulations in a High-Gradient X-Band Photoinjector

gun, emittance, electron, linac

4013

W.H. Tan, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
G. Chen, S.V. Kuzikov
Euclid TechLabs, Solon, Ohio, USA
G. Chen
IIT, Chicago, Illinois, USA
G. Ha, C.-J. Jing
ANL, Lemont, Illinois, USA
C.-J. Jing
Euclid Beamlabs, Bolingbrook, USA

A high-gradient X-band (11.7-GHz) photoinjector was recently developed by Euclid Techlabs and is in its commissioning phase at the Argonne Wakefield Accelerator (AWA). This contribution discuss the beam-dynamics modeling of the photoinjector system comprising an RF gun and linac section. We especially discuss beam-dynamics optimization of setup for an integrated proof-of-principle experiments. We also discuss the use of such a photoinjector as a witness-bunch source for a future high-gradient collinear-wakefield accelerator experiments at the AWA.
* S. V. Kuzikov, et al. these proceedings.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB129

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paper received ※ 20 May 2021 paper accepted ※ 14 July 2021 issue date ※ 31 August 2021

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THPAB141

Novel Design of a HVDC Magnetized Electron Source

solenoid, permanent-magnet, gun, simulation

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

electron, photon, emittance, vacuum

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

gun, cavity, coupling, simulation

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

electron, cavity, FEM, gun

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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THPAB156

Built-in Thermionic Electron Source for an SRF Linacs

cavity, electron, gun, SRF

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]

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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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THPAB221

Multi-Objective Optimization with ACE3P and IMPACT

cavity, simulation, lattice, interface

4223

D.A. Bizzozero, J. Qiang
LBNL, Berkeley, California, USA
L. Ge, Z. Li, C.-K. Ng, L. Xiao
SLAC, Menlo Park, California, USA

Funding: This work is supported by the Director of the Office of Science of the US Department of Energy under contracts DE-AC02-05-CH11231 and DE-AC02-76-SF00515.
Photo injector design is an important consideration in the construction of next-generation accelerators. In current injector optimization, components (e.g. RF cavities) are individually shape-optimized for performance subject to requirements such as peak surface field, shunt impedance, and resonant frequency. Once these component shapes are determined, beam dynamics simulations optimize the injector lattice by adjusting parameters such as the amplitude and phase of the driving fields. However, this form of beam dynamics optimization is restricted by the fixed geometry and field profile of the components. To optimize accelerator design more generally, a coupled optimization of the cavity shape and beam parameters is required. For this coupled optimization problem, we have created an integrated ACE3P-IMPACT workflow. Within this workflow, component geometries are adjusted, field modes are computed with Omega3P (a module in the ACE3P suite), and beam dynamics are simulated with IMPACT-T. This workflow is encapsulated into a multi-objective optimization algorithm using the DEAP* and libEnsemble** Python libraries to yield a Pareto-optimal set of solutions for a simple injector model.
* F.-A. Fortin et al, DEAP: Evolutionary Algorithms Made Easy, J Mach Learn Res, 13, 2171-2175, July 2012
** S. Hudson et al, libEnsemble User Manual, Argonne National Laboratory, Rev 0.7.1, 2020

Poster THPAB221 [1.842 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB221

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paper received ※ 19 May 2021 paper accepted ※ 02 August 2021 issue date ※ 26 August 2021

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THPAB229

Energy-Binning Fast Multipole Method for Electron Injector Simulations

space-charge, simulation, electron, multipole

4244

S.A. Schmid, H. De Gersem, E. Gjonaj
TEMF, TU Darmstadt, Darmstadt, Germany

In a high brilliance electron injector, small beam energy and large charge density give rise to strong space charge effects. Furthermore, a large relative energy spread during the beam generation modifies the space charge interaction between different regions of the particle bunch. Therefore, modeling the phase space evolution in an electron injector requires a numerically efficient particle tracking code that can handle space charge interactions of spatially and energetically strongly inhomogeneous particle distributions. We implemented an energy-binning scheme for a meshless fast multipole method (FMM). The energy-binning approximates the momentum distribution of the beam by assigning particles to adaptive tree structures defined at different Lorentz frames. Based on the tree structures, the FMM computes a hierarchical approximation for the space charge interaction of the particle bunch. We use the energy-binning FMM to simulate the beam generation in the photoinjector of the European XFEL developed at DESY-PITZ. Furthermore, we present numerical convergence and performance studies and compare the simulation results to direct particle-particle methods.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB229

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paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 13 August 2021

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THPAB313

Drive Laser System for Shanghai Soft X-Ray Free Electron Laser

laser, FEL, electron, free-electron-laser

4403

L. Feng, C.L. Li, B. Liu, J.G. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China
X. Lu
ANL, Lemont, Illinois, USA
X.T. Wang, W.Y. Zhang
Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China

In this paper, we introduce the design and layout of the drive laser of Shanghai Soft X-ray Free Electron Laser (SXFEL). It is known that the temporal and spatial distribution of the drive laser is crucial for high-quality electron beams. The drive laser provides the laser pulse of 266nm wavelength and 8ps pulse duration for the photocathode, as well as 400nm wavelength, 2-20ps tunable pulse duration for the laser heater. For this purpose, there are mainly four parts in such system, including a third-harmonic generation device, pulse stretcher, image transmitted system, and laser optical module for laser heater. Finally, the measured results of the electron beam under this drive laser system are presented and discussed.

Poster THPAB313 [0.691 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB313

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paper received ※ 20 May 2021 paper accepted ※ 15 July 2021 issue date ※ 10 August 2021

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THPAB331

High-Power Test of a Highly Over-Coupled X-Band RF Gun Driven by Short RF Pulses

gun, electron, wakefield, flattop

4432

J.H. Shao, D.S. Doran, W. Liu, J.G. Power, C. Whiteford, E.E. Wisniewski
ANL, Lemont, Illinois, USA
C.-J. Jing, S.V. Kuzikov
Euclid TechLabs, Solon, Ohio, USA
X. Lu, P. Piot, W.H. Tan
Northern Illinois University, DeKalb, Illinois, USA

Beam brightness, a key figure of merit of RF photocathode guns, can be improved by increasing the cathode surface field which suppresses emittance growth from space charge. The surface field in normal-conducting structures is mainly limited by RF breakdown and it has been experimentally discovered that RF breakdown rate exponentially depends on RF pulse length. A highly over-coupled 1.5-cell X-band photocathode gun has been developed to be powered by 9 ns RF pulses with 3 ns rising time, 3 ns flat-top, and 3 ns falling time generated by an X-band metallic power extractor. In the recent experiment at Argonne Wakefield Accelerator facility, cathode surface field up to ~350 MV/m with a low breakdown rate has been obtained under ~250 MW input power. Strong beam loading from dark current was observed during RF conditioning and quickly recovered to a negligible level after the gun reached the maximum gradient. Detailed high-power test results and data analysis will be reported in this manuscript.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB331

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paper received ※ 25 May 2021 paper accepted ※ 14 July 2021 issue date ※ 10 August 2021

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THPAB344

Magneto-Optical Trap Cathode for High Brightness Applications

electron, laser, gun, emittance

4466

V.S. Yu, C.E. Hansel, G.E. Lawler, M. Mills, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
J.I. Mann
PBPL, Los Angeles, USA

Funding: This work was performed with support of the US Department of Energy under Contract No. DE-SC0020409 and the National Science Foundation under Grant No. PHY-1549132
Electron bunches extracted from magneto-optical traps (MOTs) via femtosecond photo-ionization and electrostatic acceleration can have significantly lower transverse emittance than emissions from traditional metal cathodes. Such MOT cathodes, however, have two drawbacks: the need for multiple trapping lasers and the limit to ~MV/m fields. Designs exist for MOTs which only require one trapping laser. Our RF simulations in High-Frequency Structure Simulator (HFSS) indicate that the cone MOT is the only one compatible with high gradient RF cavities. We present the combination of the two, an RF cavity with a cone-MOT as part of its geometry. It only requires one trapping laser and can use much higher fields. The geometry of the chamber is compatible with a wide range of MOT species, which allows the search for one which is compatible with copper cavities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB344

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paper received ※ 19 May 2021 paper accepted ※ 29 July 2021 issue date ※ 31 August 2021

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THPAB349

Feed-Forward Neural Network Based Modelling of an Ultrafast Laser for Enhanced Control

laser, network, controls, electron

4478

A. Aslam, M. Martínez-Ramón, S.D. Scott
UNM-ECE, Albuquerque, USA
S. Biedron
Argonne National Laboratory, Office of Naval Research Project, Argonne, Illinois, USA
S. Biedron
Element Aero, Chicago, USA
S. Biedron
UNM-ME, Albuquerque, New Mexico, USA
M. Burger, J. Murphy
NERS-UM, Ann Arbor, Michigan, USA
K.M. Krushelnick, J. Nees, A.G.R. Thomas
University of Michigan, Ann Arbor, Michigan, USA
Y. Ma
IHEP, Beijing, People’s Republic of China
Y. Ma
Michigan University, Ann Arbor, Michigan, USA

Funding: Acknowledgements: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under award number DE-SC0019468.
The applications of machine learning in today’s world encompass all fields of life and physical sciences. In this paper, we implement a machine learning based algorithm in the context of laser physics and particle accelerators. Specifically, a neural network-based optimisation algorithm has been developed that offers enhanced control over an ultrafast femtosecond laser in comparison to the traditional Proportional Integral and derivative (PID) controls. This research opens a new potential of utilising machine learning and even deep learning techniques to improve the performance of several different lasers and accelerators systems.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB349

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paper received ※ 20 May 2021 paper accepted ※ 02 July 2021 issue date ※ 19 August 2021

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