IPAC2021 - Classification: MC7: Accelerator Technology / T31 Subsystems, Technology and Components, Other

Paper	Title	Page
MOPAB345	Machine Learning with a Hybrid Model for Monitoring of the Protection Systems of the LHC	1072
	C. Obermair, A. Apollonio, Z. Charifoulline, M. Maciejewski, A.P. Verweij CERN, Geneva, Switzerland C. Obermair, F. Pernkopf TUG, Graz, Austria
	The LHC is the world’s largest particle accelerator and uses a complex set of sophisticated and highly reliable machine protection systems to ensure a safe operation with high availability for particle physics production. The data gathered during several years of successful operation allow the use of data-driven methods to assist experts in finding anomalies in the behavior of those protection systems. In this paper, we derive a model that can extend the existing signal monitoring applications for the LHC protection systems with machine learning. Our hybrid model combines an existing threshold-based system with a SVM by using signals, manually validated by experts. Even with a limited amount of data, the SVM learns to integrate the expert knowledge and contributes to a better classification of safety-critical signals. Using this approach, we analyze historical signals of quench heaters, which are an important part of the quench protection system for superconducting magnets. Particularly, it is possible to incorporate expert decisions into the classification process and to improve the failure detection rate of the existing quench heater discharge analysis tool.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB345
About •	paper received ※ 20 May 2021 paper accepted ※ 19 July 2021 issue date ※ 01 September 2021
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TUXC06	Visualizing Lattice Dynamic Behavior by Acquiring a Single Time-Resolved MeV	1311
	X. Yang, T.V. Shaftan, V.V. Smaluk, J. Tao, L. Wu, Y. Zhu BNL, Upton, New York, USA W. Wan ShanghaiTech University, Shanghai, People’s Republic of China
	We explore the possibility of visualizing the lattice dynamic behavior by acquiring a single time-resolved MeV UED image. Conventionally, multiple UED shots with varying time delays are needed to map out the entire dynamic process. The measurement precision is limited by the timing jitter between the pulses of laser pump and UED probe. We show that, by converting the longitudinal time of an electron bunch to the transverse position of a Bragg peak on the detector, one can obtain the full lattice dynamic process in a single electron pulse. We propose a novel design of a time-resolved UED with the capability of capturing a wide range of dynamic features in a single diffraction image. The work presented here is not only an extension of the ultrashort-pulse pump/long-pulse probe scheme being used in transient spectroscopy studies for decades but also advances the capabilities of MeV UED for future applications with tunable electron probe profile and detecting time range with femtosecond resolution. Furthermore, we present numerical simulations illustrating the capability of acquiring a single time-resolved diffraction image based on the case-by-case studies of lattice dynamic behavior.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXC06
About •	paper received ※ 14 May 2021 paper accepted ※ 28 July 2021 issue date ※ 31 August 2021
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TUPAB095	Arbitrary Longitudinal Pulse Shaping with a Multi-Leaf Collimator and Emittance Exchange	1600
	N. Majernik, G. Andonian, J.B. Rosenzweig UCLA, Los Angeles, California, USA D.S. Doran, G. Ha, J.G. Power, E.E. Wisniewski ANL, Lemont, Illinois, USA R.J. Roussel Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
	Funding: DOE HEP Grant DE-SC0017648, and National Science Foundation Grant No. PHY-1549132 Drive and witness beams with variable current profiles and bunch spacing can be generated using an emittance exchange beamline (EEX) in conjunction with transverse masks. Recently, this approach was used to create advanced driver profiles and demonstrate record-breaking plasma wakefield transformer ratios [Roussel, R., et al., Phys. Rev. Lett. 124, 044802 (2020)], a crucial advancement for effective witness acceleration. Presently, these transverse masks are individually laser cut, making the refinement of beam profiles a slow process. Instead, we have proposed the used of a UHV compatible multileaf collimator (MLC) to replace these masks. An MLC permits real-time adjustment of the beam masking, permitting faster optimization in a manner highly synergistic with machine learning. Beam dynamics simulations have shown that practical MLCs offer resolution that is functionally equivalent to that offered by the laser cut masks. In this work, the engineering considerations and practical implementation of such a system at the AWA facility are discussed and the results of benchtop tests are presented. * Roussel, Ryan, et al. PRL 124.4 (2020): 044802
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB095
About •	paper received ※ 19 May 2021 paper accepted ※ 20 July 2021 issue date ※ 29 August 2021
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TUPAB193	Operation and Maintenance of Chinese Spallation Neutron Source Stripper Foil	1858
	J.X. Chen, X.J. Nie, A.X. Wang, Y.J. Yu IHEP CSNS, Guangdong Province, People’s Republic of China L. Kang, L. Liu IHEP, Beijing, People’s Republic of China J.B. Yu DNSC, Dongguan, People’s Republic of China
	Funding: The project is supported by the National Natural Science Foundation of China (Grant No.11975253) and Natural Science Foundation of Guangdong Province (Grant No.2018A030313959) The stripper foil system is the essential equipment of the spallation neutron source to achieve negative hydrogen injection. More than 99% of negative hydrogen ions complete the charge stripper in the primary stripper foil during the injection process. The remaining ions will lead to the in-dump after the secondary foil or absorbed by the negative hydrogen scraper. This paper introduces some work records of operation and maintenance of stripper foil system. stripper foil, maintenance, operation
	Poster TUPAB193 [0.395 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB193
About •	paper received ※ 12 May 2021 paper accepted ※ 11 June 2021 issue date ※ 21 August 2021
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TUPAB194	Operation Status of CSNS/RCS Transverse Collimation System	1862
	J.B. Yu, J.X. Chen, L. Liu, X.J. Nie, C.J. Ning, G.Y. Wang, A.X. Wang, J.S. Zhang IHEP CSNS, Guangdong Province, People’s Republic of China L. Kang, Q.B. Wu, S.Y. Xu IHEP, Beijing, People’s Republic of China
	Funding: Natural Science Foundation of Guangdong Province 2018A030313959 In order to meet the requirements of daily maintenance of CSNS/RCS, the transverse collimation system was designed to concentrate the uncontrollable beam loss in this region. Based on physical parameters, considering the processing technology, the area was rationally arranged; combined with the requirements of physical and radiation protection, under the premise of meeting the use requirements, fully consider the limit switch, mechanical hard limit and other components, increasing the output control signals of rotary encoder and displacement sensor, the movement of the absorbers were monitored. At present, the beam collimation system has been running with no mechanical failure for two years on CSNS, and it plays an active role in beam power boost and beam loss control, which proves that the structural design of the system is reasonable.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB194
About •	paper received ※ 17 May 2021 paper accepted ※ 11 June 2021 issue date ※ 17 August 2021
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WEPAB359	Report on Collimator Damaged Event in SuperKEKB	3541
	S. Terui, Y. Funakoshi, H. Hisamatsu, T. Ishibashi, K. Kanazawa, Y. Ohnishi, K. Shibata, M. Shirai, Y. Suetsugu, M. Tobiyama KEK, Ibaraki, Japan
	Collimator jaws for SuperKEKB main ring, which is an electron-positron collider, installed to suppress background noise in a particle detector complex named Belle II. In high current operations with 500 mA or more, jaws were occasionally damaged by hitting abnormal beams. This trouble is a low-frequency, which is once-a-commissioning period currently, but high-consequence one because we are not able to apply high voltage on detectors in Belle II by high backgrounds. At this moment this jaw damage event occurs, we observed pressure burst near the collimator with the beam abort, there was no sign of beam oscillation indicating instability, and the beam intensity suddenly decreased a few turns before the abort. I predict that the cause of this jaw damage was that a sudden change of the beam energy by the collision with dust. In this paper, the explanation of the observation result of this events and tracking simulation of beam colliding with dust are reported.
	Poster WEPAB359 [3.869 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB359
About •	paper received ※ 17 May 2021 paper accepted ※ 22 July 2021 issue date ※ 20 August 2021
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WEPAB380	Measurements of Field Emission Induced Optical Spectra	3602
	R.C. Peacock, G. Burt Lancaster University, Lancaster, United Kingdom S. Calatroni, W. Wuensch CERN, Meyrin, Switzerland
	Field emission induced optical spectra in a dc electrode system have been measured using a spectrometer and CCD camera system in order to gain insight into the nature of field emissions sites. Spectra were measured from between 2 ridged parallel copper electrodes with a gap ranging from 60µm to 100µm and a bias voltage of up to 8000V under high vacuum conditions. A strong correlation between the light intensity of the spectra and the measured field emitted current was observed as a function of applied voltage. A characteristic broadband spectrum ranging from 550nm and 850nm wavelength was observed but there were important features which varied as a function of observation angle, polarity, and conditioning state and also with time. Possible causes of the optical spectra being considered include black body radiation, optical transition radiation and cathode luminescence of copper. Further experiments are ongoing with an improved optical setup to increase optical alignment for measurements with different materials of electrodes, developing further understanding of the cause of the optical spectra, to provide understanding into characteristics and evolution of emission sites.
	Poster WEPAB380 [1.158 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB380
About •	paper received ※ 11 May 2021 paper accepted ※ 24 June 2021 issue date ※ 24 August 2021
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WEPAB381	Multipactor Simulations for MYRRHA Spoke Cavity: Comparison Between SPARK3D, MUSICC3D, CST PIC and Measurement	3606
	N. Hu, M. Chabot, J.-L. Coacolo, D. Longuevergne, G. Olry Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France M.B. Belhaj ONERA, Toulouse, France
	The multipactor effect can lead to thermal breakdown (quench), high field emission and limited accelerating gradient in superconducting accelerator devices. To determine the multipactor breakdown power level, multipactor simulations can be performed. The objective of this study is to compare the results given by different simulation codes with the results of vertical testing of SRF cavities. In this paper, Spark3D, MUSICC3D and CST Studio PIC solver have been used to simulate the multipactor effect in Spoke cavity developed within the framework of MYRRHA project. Then, a benchmark of these three simulation codes has been made. The breakdown power level, the multipactor order and the most prominent location of multipactor are presented. Finally, the simulation results are compared with the measurements done during the vertical tests.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB381
About •	paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 25 August 2021
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WEPAB383	An Evolutionary Algorithm Approach to Multi-Pass ERL Optics Design	3610
	I. Neththikumara, T. Satogata ODU, Norfolk, Virginia, USA R.M. Bodenstein, S.A. Bogacz, T. Satogata JLab, Newport News, Virginia, USA A. Vandenhoeke ULB, Bruxelles, Belgium
	Funding: This material is based upon work supported by the U.S. Department of Energy under contract DE-AC05-06OR23177. An Energy Recovery Experiment at CEBAF (ER@CEBAF) is aimed at demonstrating high energy, low current, multi-pass energy recovery at the existing 12 GeV CEBAF accelerator. The beam break-up instability, limiting the maximum beam current, can be controlled through minimizing beta functions for the lowest energy pass, which gives a preference to strongly focusing optics, e.g. a semi-periodic FODO lattice. On the other hand, one needs to limit beta function excursions, caused by under focusing, at the higher energy passes, which in turn favors weakly focusing linac optics. Balancing both effects is the main objective of proposed multi-pass linac optics optimization. Here, we discuss an optics design process for ER@CEBAF transverse optics using a genetic algorithm.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB383
About •	paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 15 August 2021
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WEPAB384	Design and Beam Dynamics of the Electron Lens for Space Charge Compensation in SIS18	3614
	S. Artikova, D. Ondreka, K. Schulte-Urlichs, P.J. Spiller GSI, Darmstadt, Germany
	An electron lens for space charge compensation is being developed at GSI to increase the ion beam intensities in SIS18 for the FAIR project. It uses an electron beam of 10A maximum current at 30keV. The maximum magnetic field on-axis is 0.6T, considerably higher than the field of the existing electron cooler. The magnetic system of the lens consists of solenoids and toroids. The toroids’ vertical field component creates a significant horizontal orbit deflection in the circulating low rigidity ion beam. To correct this deflection, four correction dipoles have been introduced. As common for electron lenses, the high-power electron beam is not dumped at ground potential, but rather in a collector with a small bias potential with respect to the cathode. The present design foresees a collector at -27kV, leading to a power dissipation of 30kW, distributed over a large surface area by placing the collector in an appropriately shaped magnetic field of a pre-collector solenoid. This contribution reports on the design of the lens and presents the results of beam transport simulations for the electron beam (with space charge) and a representative ion beam, performed using the 3D CST STUDIO.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB384
About •	paper received ※ 20 May 2021 paper accepted ※ 05 July 2021 issue date ※ 31 August 2021
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WEPAB385	Beam Dynamic Analysis of RF Modulated Electron Beam Produced by Gridded Thermionic Guns	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 ※ 30 August 2021
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WEPAB387	Study of Failure Modes in Electron Linac-Based X-Ray Sources for Industrial Applications	3622
	K.P. Dixit, G. Vinod BARC, Mumbai, India
	Electron linac-based X-ray sources (XRS) have an increased demand in industrial applications, mainly for their advantages of compactness and ease of use. In order to achieve reliable operation, it is necessary to have rugged components in the linac system. Hence, this study focusses on achieving high reliability design; also in formulating a preventive maintenance programme to optimise the availability and prognostic methods for performance monitoring of components. This paper investigates the failure modes in the important sub-systems of a 6 MeV electron linac, including electron gun, RF power source, vacuum system, x-ray target, control system, etc. Electron guns suffer from problems related to the filament heater damage and high voltage insulation failure. In the RF source, major components (line-type pulsed modulators, magnetrons, circulator and RF window) are studied to assess their life. Fault tree analysis of the individual sub-systems and the effect of individual failures on the linac down-time are studied. A few mitigation techniques used in practical systems are also discussed here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB387
About •	paper received ※ 18 May 2021 paper accepted ※ 23 July 2021 issue date ※ 29 August 2021
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WEPAB390	High-Quality, Conformal Bellows Coatings Using Ultra-Fast HiPIMS with Precision Ion Energy Control	3626
	T.J. Houlahan, I. Haehnlein, W.M. Huber, B.E. Jurczyk, I.A. Shchelkanov, R.A. Stubbers Starfire Industries LLC, Champaign, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy under Award Number DE-SC0020481. In this paper we demonstrate a replacement for traditional ’wet’ chemical deposition processes using a vacuum, ionized physical vapor deposition (iPVD) process that results in a conformal metal film, capable of coating complex, convoluted parts that are common in modern particle accelerators (e.g., bellows, RF cavities). Results are presented for a process utilizing the combined deposition and etching that are achieved using ultra-fast high-power impulse magnetron sputtering (HiPIMS) coupled with precision control of the ion energy using a positive voltage reversal. This process results in a conformal film and has been used to coat both test coupons and full bellows assemblies. The resulting Cu films, which are 5-10 µm in thickness, exhibit excellent adhesion. Further, they have been shown to tolerate temperature extremes ranging from 77 K to a 400 C vacuum bakeout as well as extreme plastic deformation of the substrate without any buckling, cracking, or delamination.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB390
About •	paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 31 August 2021
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WEPAB394	Development of a New Interlock and Data Acquisition for the RF System at High Energy Photon Source	3630
	Z.W. Deng, J.P. Dai, H.Y. Lin, Q.Y. Wang, P. Zhang IHEP, Beijing, People’s Republic of China
	Funding: This work was supported by High Energy Photon Source, a major national science and technology infrastructure in China. A new interlock and data acquisition (DAQ) system is being developed for the RF system at High Energy Photon Source (HEPS) to protect essential devices as well as to locate the fault. Various signals collected and pre-processed by the DAQ system and individual interlock signals from solid-state power amplifiers, low-level RFs, arc detectors, etc. are sent to the interlock system for logic decision to control the RF switch. Programmable logic controllers (PLC) are used to collect slow signals like temperature, water flowrate, etc., while fast acquisition for RF signals is realized by dedicated boards with down-conversion frontend and digital signal processing boards. In order to improve the response time, field programmable gate array (FPGA) has been used for interlock logic implementation with an embedded experimental physics and industrial control system (EPICS). Data storage is managed by using EPICS Archiver Appliance and an operator interface is developed by using Control System Studio (CSS) running on a standalone computer. This paper presents the design and the first test of the new interlock and DAQ for HEPS RF system.
	Poster WEPAB394 [2.140 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB394
About •	paper received ※ 16 May 2021 paper accepted ※ 14 July 2021 issue date ※ 31 August 2021
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WEPAB396	First Measurements on Multipactor Study	3633
	Y. Gómez Martínez, J. Angot, M.A. Baylac, T. Cabanel, P.-O. Dumont, N. Emeriaud, O. Zimmermann LPSC, Grenoble Cedex, France D. Longuevergne FLUO, Orsay, France G. Sattonnay Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
	Multipactor (MP) is an undesired phenomenon of resonant electron build up encountered on particle accelerators. It can induce anomalous thermal losses, higher than the Joule losses, inducing a decrease of the superconducting cavities quality factor, it can even lead to a cavity quench. On couplers, it can produce irreversible damages or generate a breakdown of their vacuum window. Multipactor may lead to Electron Cloud build up as well. The accelerator group at LPSC has developed a test bench dedicated to the multipactor studies. This paper presents the experimental set-up and its first measurements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB396
About •	paper received ※ 18 May 2021 paper accepted ※ 14 July 2021 issue date ※ 17 August 2021
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WEPAB397	Design of the Two-Layer Girder for Accelerating Tube	3636
	X.J. Nie, H.Y. He, L. Kang IHEP, Beijing, People’s Republic of China J.X. Chen, L. Liu, R.H. Liu, C.J. Ning, A.X. Wang, G.Y. Wang, Y.J. Yu, J.S. Zhang, D.H. Zhu IHEP CSNS, Guangdong Province, People’s Republic of China J.B. Yu DNSC, Dongguan, People’s Republic of China
	An accelerating tube is one kind of important acceleration equipment of a linear accelerator. It is often made up of oxygen-free copper with a long tubular structure. It’s easy to suffer from deformation. Based on support requirements, the reasonable structure of the girder was obtained. Four supporting blocks were installed on the top surface of aluminum profile with the uniform distribution along the beam direction. The support strength with static condition and different working conditions were checked by ANSYS simulation calculation to ensure the stable operation of the girder. The two-layer girder can be used as a reference for other similar slender part for its simple structure and reliable support.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB397
About •	paper received ※ 14 May 2021 paper accepted ※ 01 September 2021 issue date ※ 22 August 2021
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WEPAB398	A C-Band RF Mode Launcher with Quadrupole Field Components Cancellation for High Brightness Applications	3638
	G. Pedrocchi SBAI, Roma, Italy D. Alesini, F. Cardelli, A. Gallo, A. Giribono, B. Spataro INFN/LNF, Frascati, Italy G. Castorina AVO-ADAM, Meyrin, Switzerland L. Ficcadenti INFN-Roma, Roma, Italy M. Migliorati, A. Mostacci, L. Palumbo Sapienza University of Rome, Rome, Italy
	The R&D of high gradient radiofrequency devices is aimed to develop innovative and compact accelerating stuctures based on new manufactoring techniques and materials in order to produce devices operating with the highest accelerating gradient. Recent studies have shown a large increase in the maximum sustained RF surface electric fields in copper structure operating at cryogenic temperature. These novel approaches allow significant performance improvements of RF photoinjectors. Indeed the operation at high surface fields results in considerable increase of electron brilliance. This requires high field quality in the RF photoinjector and specifically in its poweer coupler. In this work we present a novel power coupler for the RF photoinjector. The coupler is a compact C-band TM01 mode launcher with a fourfold symmetry which minimized both the dipole and the quadrupole RF field components.
	Poster WEPAB398 [1.799 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB398
About •	paper received ※ 13 May 2021 paper accepted ※ 06 July 2021 issue date ※ 23 August 2021
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Paper

Title

Page

Machine Learning with a Hybrid Model for Monitoring of the Protection Systems of the LHC

1072

C. Obermair, A. Apollonio, Z. Charifoulline, M. Maciejewski, A.P. Verweij
CERN, Geneva, Switzerland
C. Obermair, F. Pernkopf
TUG, Graz, Austria

The LHC is the world’s largest particle accelerator and uses a complex set of sophisticated and highly reliable machine protection systems to ensure a safe operation with high availability for particle physics production. The data gathered during several years of successful operation allow the use of data-driven methods to assist experts in finding anomalies in the behavior of those protection systems. In this paper, we derive a model that can extend the existing signal monitoring applications for the LHC protection systems with machine learning. Our hybrid model combines an existing threshold-based system with a SVM by using signals, manually validated by experts. Even with a limited amount of data, the SVM learns to integrate the expert knowledge and contributes to a better classification of safety-critical signals. Using this approach, we analyze historical signals of quench heaters, which are an important part of the quench protection system for superconducting magnets. Particularly, it is possible to incorporate expert decisions into the classification process and to improve the failure detection rate of the existing quench heater discharge analysis tool.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB345

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paper received ※ 20 May 2021 paper accepted ※ 19 July 2021 issue date ※ 01 September 2021

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TUXC06

Visualizing Lattice Dynamic Behavior by Acquiring a Single Time-Resolved MeV

1311

X. Yang, T.V. Shaftan, V.V. Smaluk, J. Tao, L. Wu, Y. Zhu
BNL, Upton, New York, USA
W. Wan
ShanghaiTech University, Shanghai, People’s Republic of China

We explore the possibility of visualizing the lattice dynamic behavior by acquiring a single time-resolved MeV UED image. Conventionally, multiple UED shots with varying time delays are needed to map out the entire dynamic process. The measurement precision is limited by the timing jitter between the pulses of laser pump and UED probe. We show that, by converting the longitudinal time of an electron bunch to the transverse position of a Bragg peak on the detector, one can obtain the full lattice dynamic process in a single electron pulse. We propose a novel design of a time-resolved UED with the capability of capturing a wide range of dynamic features in a single diffraction image. The work presented here is not only an extension of the ultrashort-pulse pump/long-pulse probe scheme being used in transient spectroscopy studies for decades but also advances the capabilities of MeV UED for future applications with tunable electron probe profile and detecting time range with femtosecond resolution. Furthermore, we present numerical simulations illustrating the capability of acquiring a single time-resolved diffraction image based on the case-by-case studies of lattice dynamic behavior.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXC06

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paper received ※ 14 May 2021 paper accepted ※ 28 July 2021 issue date ※ 31 August 2021

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TUPAB095

Arbitrary Longitudinal Pulse Shaping with a Multi-Leaf Collimator and Emittance Exchange

1600

N. Majernik, G. Andonian, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
D.S. Doran, G. Ha, J.G. Power, E.E. Wisniewski
ANL, Lemont, Illinois, USA
R.J. Roussel
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA

Funding: DOE HEP Grant DE-SC0017648, and National Science Foundation Grant No. PHY-1549132
Drive and witness beams with variable current profiles and bunch spacing can be generated using an emittance exchange beamline (EEX) in conjunction with transverse masks. Recently, this approach was used to create advanced driver profiles and demonstrate record-breaking plasma wakefield transformer ratios [Roussel, R., et al., Phys. Rev. Lett. 124, 044802 (2020)], a crucial advancement for effective witness acceleration. Presently, these transverse masks are individually laser cut, making the refinement of beam profiles a slow process. Instead, we have proposed the used of a UHV compatible multileaf collimator (MLC) to replace these masks. An MLC permits real-time adjustment of the beam masking, permitting faster optimization in a manner highly synergistic with machine learning. Beam dynamics simulations have shown that practical MLCs offer resolution that is functionally equivalent to that offered by the laser cut masks. In this work, the engineering considerations and practical implementation of such a system at the AWA facility are discussed and the results of benchtop tests are presented.
* Roussel, Ryan, et al. PRL 124.4 (2020): 044802

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB095

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paper received ※ 19 May 2021 paper accepted ※ 20 July 2021 issue date ※ 29 August 2021

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TUPAB193

Operation and Maintenance of Chinese Spallation Neutron Source Stripper Foil

1858

J.X. Chen, X.J. Nie, A.X. Wang, Y.J. Yu
IHEP CSNS, Guangdong Province, People’s Republic of China
L. Kang, L. Liu
IHEP, Beijing, People’s Republic of China
J.B. Yu
DNSC, Dongguan, People’s Republic of China

Funding: The project is supported by the National Natural Science Foundation of China (Grant No.11975253) and Natural Science Foundation of Guangdong Province (Grant No.2018A030313959)
The stripper foil system is the essential equipment of the spallation neutron source to achieve negative hydrogen injection. More than 99% of negative hydrogen ions complete the charge stripper in the primary stripper foil during the injection process. The remaining ions will lead to the in-dump after the secondary foil or absorbed by the negative hydrogen scraper. This paper introduces some work records of operation and maintenance of stripper foil system.
stripper foil, maintenance, operation

Poster TUPAB193 [0.395 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB193

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paper received ※ 12 May 2021 paper accepted ※ 11 June 2021 issue date ※ 21 August 2021

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TUPAB194

Operation Status of CSNS/RCS Transverse Collimation System

1862

J.B. Yu, J.X. Chen, L. Liu, X.J. Nie, C.J. Ning, G.Y. Wang, A.X. Wang, J.S. Zhang
IHEP CSNS, Guangdong Province, People’s Republic of China
L. Kang, Q.B. Wu, S.Y. Xu
IHEP, Beijing, People’s Republic of China

Funding: Natural Science Foundation of Guangdong Province 2018A030313959
In order to meet the requirements of daily maintenance of CSNS/RCS, the transverse collimation system was designed to concentrate the uncontrollable beam loss in this region. Based on physical parameters, considering the processing technology, the area was rationally arranged; combined with the requirements of physical and radiation protection, under the premise of meeting the use requirements, fully consider the limit switch, mechanical hard limit and other components, increasing the output control signals of rotary encoder and displacement sensor, the movement of the absorbers were monitored. At present, the beam collimation system has been running with no mechanical failure for two years on CSNS, and it plays an active role in beam power boost and beam loss control, which proves that the structural design of the system is reasonable.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB194

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paper received ※ 17 May 2021 paper accepted ※ 11 June 2021 issue date ※ 17 August 2021

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WEPAB359

Report on Collimator Damaged Event in SuperKEKB

3541

S. Terui, Y. Funakoshi, H. Hisamatsu, T. Ishibashi, K. Kanazawa, Y. Ohnishi, K. Shibata, M. Shirai, Y. Suetsugu, M. Tobiyama
KEK, Ibaraki, Japan

Collimator jaws for SuperKEKB main ring, which is an electron-positron collider, installed to suppress background noise in a particle detector complex named Belle II. In high current operations with 500 mA or more, jaws were occasionally damaged by hitting abnormal beams. This trouble is a low-frequency, which is once-a-commissioning period currently, but high-consequence one because we are not able to apply high voltage on detectors in Belle II by high backgrounds. At this moment this jaw damage event occurs, we observed pressure burst near the collimator with the beam abort, there was no sign of beam oscillation indicating instability, and the beam intensity suddenly decreased a few turns before the abort. I predict that the cause of this jaw damage was that a sudden change of the beam energy by the collision with dust. In this paper, the explanation of the observation result of this events and tracking simulation of beam colliding with dust are reported.

Poster WEPAB359 [3.869 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB359

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paper received ※ 17 May 2021 paper accepted ※ 22 July 2021 issue date ※ 20 August 2021

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WEPAB380

Measurements of Field Emission Induced Optical Spectra

3602

R.C. Peacock, G. Burt
Lancaster University, Lancaster, United Kingdom
S. Calatroni, W. Wuensch
CERN, Meyrin, Switzerland

Field emission induced optical spectra in a dc electrode system have been measured using a spectrometer and CCD camera system in order to gain insight into the nature of field emissions sites. Spectra were measured from between 2 ridged parallel copper electrodes with a gap ranging from 60µm to 100µm and a bias voltage of up to 8000V under high vacuum conditions. A strong correlation between the light intensity of the spectra and the measured field emitted current was observed as a function of applied voltage. A characteristic broadband spectrum ranging from 550nm and 850nm wavelength was observed but there were important features which varied as a function of observation angle, polarity, and conditioning state and also with time. Possible causes of the optical spectra being considered include black body radiation, optical transition radiation and cathode luminescence of copper. Further experiments are ongoing with an improved optical setup to increase optical alignment for measurements with different materials of electrodes, developing further understanding of the cause of the optical spectra, to provide understanding into characteristics and evolution of emission sites.

Poster WEPAB380 [1.158 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB380

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paper received ※ 11 May 2021 paper accepted ※ 24 June 2021 issue date ※ 24 August 2021

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WEPAB381

Multipactor Simulations for MYRRHA Spoke Cavity: Comparison Between SPARK3D, MUSICC3D, CST PIC and Measurement

3606

N. Hu, M. Chabot, J.-L. Coacolo, D. Longuevergne, G. Olry
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
M.B. Belhaj
ONERA, Toulouse, France

The multipactor effect can lead to thermal breakdown (quench), high field emission and limited accelerating gradient in superconducting accelerator devices. To determine the multipactor breakdown power level, multipactor simulations can be performed. The objective of this study is to compare the results given by different simulation codes with the results of vertical testing of SRF cavities. In this paper, Spark3D, MUSICC3D and CST Studio PIC solver have been used to simulate the multipactor effect in Spoke cavity developed within the framework of MYRRHA project. Then, a benchmark of these three simulation codes has been made. The breakdown power level, the multipactor order and the most prominent location of multipactor are presented. Finally, the simulation results are compared with the measurements done during the vertical tests.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB381

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paper received ※ 19 May 2021 paper accepted ※ 24 June 2021 issue date ※ 25 August 2021

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WEPAB383

An Evolutionary Algorithm Approach to Multi-Pass ERL Optics Design

3610

I. Neththikumara, T. Satogata
ODU, Norfolk, Virginia, USA
R.M. Bodenstein, S.A. Bogacz, T. Satogata
JLab, Newport News, Virginia, USA
A. Vandenhoeke
ULB, Bruxelles, Belgium

Funding: This material is based upon work supported by the U.S. Department of Energy under contract DE-AC05-06OR23177.
An Energy Recovery Experiment at CEBAF (ER@CEBAF) is aimed at demonstrating high energy, low current, multi-pass energy recovery at the existing 12 GeV CEBAF accelerator. The beam break-up instability, limiting the maximum beam current, can be controlled through minimizing beta functions for the lowest energy pass, which gives a preference to strongly focusing optics, e.g. a semi-periodic FODO lattice. On the other hand, one needs to limit beta function excursions, caused by under focusing, at the higher energy passes, which in turn favors weakly focusing linac optics. Balancing both effects is the main objective of proposed multi-pass linac optics optimization. Here, we discuss an optics design process for ER@CEBAF transverse optics using a genetic algorithm.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB383

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paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 15 August 2021

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WEPAB384

Design and Beam Dynamics of the Electron Lens for Space Charge Compensation in SIS18

3614

S. Artikova, D. Ondreka, K. Schulte-Urlichs, P.J. Spiller
GSI, Darmstadt, Germany

An electron lens for space charge compensation is being developed at GSI to increase the ion beam intensities in SIS18 for the FAIR project. It uses an electron beam of 10A maximum current at 30keV. The maximum magnetic field on-axis is 0.6T, considerably higher than the field of the existing electron cooler. The magnetic system of the lens consists of solenoids and toroids. The toroids’ vertical field component creates a significant horizontal orbit deflection in the circulating low rigidity ion beam. To correct this deflection, four correction dipoles have been introduced. As common for electron lenses, the high-power electron beam is not dumped at ground potential, but rather in a collector with a small bias potential with respect to the cathode. The present design foresees a collector at -27kV, leading to a power dissipation of 30kW, distributed over a large surface area by placing the collector in an appropriately shaped magnetic field of a pre-collector solenoid. This contribution reports on the design of the lens and presents the results of beam transport simulations for the electron beam (with space charge) and a representative ion beam, performed using the 3D CST STUDIO.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB384

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paper received ※ 20 May 2021 paper accepted ※ 05 July 2021 issue date ※ 31 August 2021

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WEPAB385

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

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 ※ 30 August 2021

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WEPAB387

Study of Failure Modes in Electron Linac-Based X-Ray Sources for Industrial Applications

3622

K.P. Dixit, G. Vinod
BARC, Mumbai, India

Electron linac-based X-ray sources (XRS) have an increased demand in industrial applications, mainly for their advantages of compactness and ease of use. In order to achieve reliable operation, it is necessary to have rugged components in the linac system. Hence, this study focusses on achieving high reliability design; also in formulating a preventive maintenance programme to optimise the availability and prognostic methods for performance monitoring of components. This paper investigates the failure modes in the important sub-systems of a 6 MeV electron linac, including electron gun, RF power source, vacuum system, x-ray target, control system, etc. Electron guns suffer from problems related to the filament heater damage and high voltage insulation failure. In the RF source, major components (line-type pulsed modulators, magnetrons, circulator and RF window) are studied to assess their life. Fault tree analysis of the individual sub-systems and the effect of individual failures on the linac down-time are studied. A few mitigation techniques used in practical systems are also discussed here.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB387

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paper received ※ 18 May 2021 paper accepted ※ 23 July 2021 issue date ※ 29 August 2021

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WEPAB390

High-Quality, Conformal Bellows Coatings Using Ultra-Fast HiPIMS with Precision Ion Energy Control

3626

T.J. Houlahan, I. Haehnlein, W.M. Huber, B.E. Jurczyk, I.A. Shchelkanov, R.A. Stubbers
Starfire Industries LLC, Champaign, USA

Funding: This material is based upon work supported by the U.S. Department of Energy under Award Number DE-SC0020481.
In this paper we demonstrate a replacement for traditional ’wet’ chemical deposition processes using a vacuum, ionized physical vapor deposition (iPVD) process that results in a conformal metal film, capable of coating complex, convoluted parts that are common in modern particle accelerators (e.g., bellows, RF cavities). Results are presented for a process utilizing the combined deposition and etching that are achieved using ultra-fast high-power impulse magnetron sputtering (HiPIMS) coupled with precision control of the ion energy using a positive voltage reversal. This process results in a conformal film and has been used to coat both test coupons and full bellows assemblies. The resulting Cu films, which are 5-10 µm in thickness, exhibit excellent adhesion. Further, they have been shown to tolerate temperature extremes ranging from 77 K to a 400 C vacuum bakeout as well as extreme plastic deformation of the substrate without any buckling, cracking, or delamination.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB390

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paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 31 August 2021

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WEPAB394

Development of a New Interlock and Data Acquisition for the RF System at High Energy Photon Source

3630

Z.W. Deng, J.P. Dai, H.Y. Lin, Q.Y. Wang, P. Zhang
IHEP, Beijing, People’s Republic of China

Funding: This work was supported by High Energy Photon Source, a major national science and technology infrastructure in China.
A new interlock and data acquisition (DAQ) system is being developed for the RF system at High Energy Photon Source (HEPS) to protect essential devices as well as to locate the fault. Various signals collected and pre-processed by the DAQ system and individual interlock signals from solid-state power amplifiers, low-level RFs, arc detectors, etc. are sent to the interlock system for logic decision to control the RF switch. Programmable logic controllers (PLC) are used to collect slow signals like temperature, water flowrate, etc., while fast acquisition for RF signals is realized by dedicated boards with down-conversion frontend and digital signal processing boards. In order to improve the response time, field programmable gate array (FPGA) has been used for interlock logic implementation with an embedded experimental physics and industrial control system (EPICS). Data storage is managed by using EPICS Archiver Appliance and an operator interface is developed by using Control System Studio (CSS) running on a standalone computer. This paper presents the design and the first test of the new interlock and DAQ for HEPS RF system.

Poster WEPAB394 [2.140 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB394

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paper received ※ 16 May 2021 paper accepted ※ 14 July 2021 issue date ※ 31 August 2021

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WEPAB396

First Measurements on Multipactor Study

3633

Y. Gómez Martínez, J. Angot, M.A. Baylac, T. Cabanel, P.-O. Dumont, N. Emeriaud, O. Zimmermann
LPSC, Grenoble Cedex, France
D. Longuevergne
FLUO, Orsay, France
G. Sattonnay
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France

Multipactor (MP) is an undesired phenomenon of resonant electron build up encountered on particle accelerators. It can induce anomalous thermal losses, higher than the Joule losses, inducing a decrease of the superconducting cavities quality factor, it can even lead to a cavity quench. On couplers, it can produce irreversible damages or generate a breakdown of their vacuum window. Multipactor may lead to Electron Cloud build up as well. The accelerator group at LPSC has developed a test bench dedicated to the multipactor studies. This paper presents the experimental set-up and its first measurements.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB396

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paper received ※ 18 May 2021 paper accepted ※ 14 July 2021 issue date ※ 17 August 2021

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WEPAB397

Design of the Two-Layer Girder for Accelerating Tube

3636

X.J. Nie, H.Y. He, L. Kang
IHEP, Beijing, People’s Republic of China
J.X. Chen, L. Liu, R.H. Liu, C.J. Ning, A.X. Wang, G.Y. Wang, Y.J. Yu, J.S. Zhang, D.H. Zhu
IHEP CSNS, Guangdong Province, People’s Republic of China
J.B. Yu
DNSC, Dongguan, People’s Republic of China

An accelerating tube is one kind of important acceleration equipment of a linear accelerator. It is often made up of oxygen-free copper with a long tubular structure. It’s easy to suffer from deformation. Based on support requirements, the reasonable structure of the girder was obtained. Four supporting blocks were installed on the top surface of aluminum profile with the uniform distribution along the beam direction. The support strength with static condition and different working conditions were checked by ANSYS simulation calculation to ensure the stable operation of the girder. The two-layer girder can be used as a reference for other similar slender part for its simple structure and reliable support.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB397

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paper received ※ 14 May 2021 paper accepted ※ 01 September 2021 issue date ※ 22 August 2021

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WEPAB398

A C-Band RF Mode Launcher with Quadrupole Field Components Cancellation for High Brightness Applications

3638

G. Pedrocchi
SBAI, Roma, Italy
D. Alesini, F. Cardelli, A. Gallo, A. Giribono, B. Spataro
INFN/LNF, Frascati, Italy
G. Castorina
AVO-ADAM, Meyrin, Switzerland
L. Ficcadenti
INFN-Roma, Roma, Italy
M. Migliorati, A. Mostacci, L. Palumbo
Sapienza University of Rome, Rome, Italy

The R&D of high gradient radiofrequency devices is aimed to develop innovative and compact accelerating stuctures based on new manufactoring techniques and materials in order to produce devices operating with the highest accelerating gradient. Recent studies have shown a large increase in the maximum sustained RF surface electric fields in copper structure operating at cryogenic temperature. These novel approaches allow significant performance improvements of RF photoinjectors. Indeed the operation at high surface fields results in considerable increase of electron brilliance. This requires high field quality in the RF photoinjector and specifically in its poweer coupler. In this work we present a novel power coupler for the RF photoinjector. The coupler is a compact C-band TM01 mode launcher with a fourfold symmetry which minimized both the dipole and the quadrupole RF field components.

Poster WEPAB398 [1.799 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB398

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paper received ※ 13 May 2021 paper accepted ※ 06 July 2021 issue date ※ 23 August 2021

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