Machine Parameter Measurements
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TUPP24 LOCO Corrections for Beam Trajectory Optimisation on the ISIS Accelerator 70
 
  • E.J. Brookes, H.V. Cavanagh, B. Jones
    STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
 
  The ISIS facility at the Rutherford Appleton Laboratory, UK, produces neutron and muon beams for condensed matter research. Its 50 Hz, 800 MeV proton synchrotron delivers a mean beam power of 0.2 MW to two tungsten spallation targets. The beam optics correction technique implemented in this work is Linear Optics from Closed Orbits (LOCO). LOCO modifies existing accelerator models according to a measured orbit-response matrix (ORM). This correction technique identifies imperfections in the machine lattice, and discrepancies between the machine and model. The identification of erroneous elements through analysis of the measured ORM is demonstrated in this work. In comparison to the operational settings achieved through the existing correction techniques, the initial test of the LOCO code demonstrates a 17 % improvement to the RMS trajectory deviation in the horizontal plane.  
poster icon Poster TUPP24 [0.607 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-TUPP24  
About • paper received ※ 05 September 2020       paper accepted ※ 17 September 2020       issue date ※ 30 October 2020  
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TUPP27
Monitor for Microbunching Instability in X-ray Free Electron Laser  
 
  • C. Kim, H.-S. Kang, G. Kim, I.S. Ko, J.H. Ko
    PAL, Pohang, Republic of Korea
 
  The microbunching instability is an important issue in an X-ray Free Electron Laser (XFEL) because the intensity of the FEL can be reduced significantly when the microbunching instability is generated. In the X-ray Free Electron Laser of the Pohang Accelerator Laboratory (PAL-XFEL), a visible CCD camera was installed in the existing coherent radiation monitor (CRM) for the bunch length monitoring. The measurement result shows that the CCD camera can be used as a direct monitor to diagnose the microbunching instability and can be used to optimize the FEL lasing in the PAL-XFEL.  
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TUPP28 Simulation of Cherenkov Diffraction Radiation for Various Radiator Designs 73
 
  • K. Łasocha
    Jagiellonian University, Kraków, Poland
  • D.M. Harryman
    JAI, Egham, Surrey, United Kingdom
  • T. Lefèvre, N. Mounet
    CERN, Meyrin, Switzerland
  • A. Schloegelhofer
    TU Vienna, Wien, Austria
 
  Studies performed during the last few years at different facilities have indicated that the emission of Cherenkov Diffraction Radiation (ChDR) can be exploited for a range of non-invasive diagnostics. The question remains of how to choose an optimal dielectric material and which radiator shapes give the most promising results. This contribution presents a semi-analytical framework for calculating the electromagnetic field of a charged particle beam, taking into consideration its interaction with surrounding structures. It allows us to directly compute ChDR at arbitrary probe positions inside the radiator. Several configurations will be discussed and presented, including flat and cylindrical radiators of various dimensions and electrical properties, as well as multilayer structures obtained by adding coatings of metallic nanolayers.  
poster icon Poster TUPP28 [0.400 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-TUPP28  
About • paper received ※ 01 September 2020       paper accepted ※ 14 September 2020       issue date ※ 30 October 2020  
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TUPP30
Non-Invasive Dispersion Function Measurement During Light Source Operations  
 
  • B. Podobedov, Y. Hidaka
    BNL, Upton, New York, USA
 
  We implemented a completely parasitic measurement of lattice dispersion functions in both horizontal and vertical planes, which is fully compatible with light source user operations. The measurement is performed by applying principle component analysis and adaptive filtering to very small residual orbit noise components introduced by the RF system and detected in the beam orbit data, sampled at 10 kHz. No changes in RF frequency are required. The measurement, presently performed once a minute, was shown to be robust and immune to changes in the beam current, residual orbit noise amplitude and frequency content as well as other factors. At low current it was shown to provide similar accuracy to the traditional method (which shifts the 500 MHz RF frequency by ±500 Hz). In this paper we will explain our measurement technique and present typical dispersion function stability achieved during NSLS-II operations.  
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TUPP31
Micro-Bunching Measurements at FERMI  
 
  • M. Veronese, E. Allaria, S. Di Mitri, M. Ferianis, L. Giannessi, G. Penco, P. Rebernik Ribič, S. Spampinati, C. Spezzani, M. Trovò
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • E. Ferrari
    PSI, Villigen PSI, Switzerland
  • G. Perosa
    Università degli Studi di Trieste, Trieste, Italy
  • P. Rebernik Ribič
    University of Nova Gorica, Nova Gorica, Slovenia
  • E. Roussel
    PhLAM/CERLA, Villeneuve d’Ascq, France
 
  The origin and evolution of micro-bunching (u-B) in a LINAC is very important for Free Electron laser (FEL), a key knowledge to full control and highest quality of the FEL radiation. The experimental u-B characterization is not simple, due to the measurement complexity, considering the u-B extended spectral range and its interplay with other machine effects. At FERMI, we have measured u-B signatures using different techniques, including intensity characterization of Coherent OTR(visible range) and the FFT based modulation analysis performed on the spectrometer images. The latter available both at the first bunch compressor and at the diagnostics beam dump. The beating of two laser pulses at laser heater has been used to induce narrow-band micro-bunching modulations, used as a known probe, to study the FEL / u-B instability spectra. As spectral measurement technique, the distribution of Coherent-TR in the IR region, using BP filters and PbSe detectors, has been implemented. More recently, a new IR spectrometer based on a CaF2 prism and a scanning technique has been developed and installed. Here we present techniques and the experimental results obtained and future perspectives.  
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WEPP27 An Alternative Processing Algorithm for the Tune Measurement System in the LHC 162
 
  • L. Grech, D. Alves, M. Gąsior, S. Jackson, O.R. Jones, T.E. Levens, J. Wenninger
    CERN, Meyrin, Switzerland
  • G. Valentino
    University of Malta, Information and Communication Technology, Msida, Malta
 
  The betatron tune in the Large Hadron Collider (LHC) is measured using a Base-Band-Tune (BBQ) system. Processing of these BBQ signals is often perturbed by 50Hz noise harmonics present in the beam. This causes the tune measurement algorithm, currently based on peak detection, to provide incorrect tune estimates during the acceleration cycle with values that clearly oscillate between neighbouring harmonics. The LHC tune feedback cannot be used to its full extent in these conditions as it relies on stable and reliable tune estimates. In this work we present two alternative tune measurement algorithms, designed to mitigate this problem by ignoring small frequency bands around the 50Hz harmonics and estimating the tune from spectra with gaps. One is based on Gaussian Processes and the other is based on a weighted moving average. We compare the tune estimates of the new and present algorithms and put forward a proposal that can be implemented during the renovation of the BBQ system for the next physics run of the LHC.  
poster icon Poster WEPP27 [1.564 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-WEPP27  
About • paper received ※ 02 September 2020       paper accepted ※ 18 September 2020       issue date ※ 30 October 2020  
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WEPP28 High-Accuracy Diagnostic Tool for Beam Position Monitor Troubleshooting in SSRF Based on Clustering Analysis 166
 
  • R. Jiang, J. Chen, Y.B. Leng
    SSRF, Shanghai, People’s Republic of China
 
  Beam position monitors (BPMs) are important to monitor the beam moving steadily. In spite of some data is viewed and analysed, a large fraction of data has never been effectively analysed in accelerator operation. It lead to some useful information not coming to the surface during the beam position monitor troubleshooting processing. We will describe in this paper our efforts to use clustering analysis techniques to pull out new information from existing beam data. Our focus has been to look at malfunction of BPM, associating basic running data that is ß oscillation of X and Y directions, energy oscillation and doing predictive analysis. Clustering analysis results showed that 140 BPMs could be classify into normal group and fault group and abnormal BPM could be separated. Based on the results, the algorithm could locate fault BPM and it could be an effective supplement for data analysis in accelerator physics.  
poster icon Poster WEPP28 [0.876 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-WEPP28  
About • paper received ※ 02 September 2020       paper accepted ※ 18 September 2020       issue date ※ 30 October 2020  
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WEPP29 Energy Gain Measurement for Electrons Accelerated in a Single-Cycle THz Structure 170
 
  • S.V. Kuzikov, S.P. Antipov, P.V. Avrakhov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • S. Bodrov, A.E. Fedotov, A.N. Stepanov, A.A. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
 
  Funding: This work in a part of THz structure simulations was supported by Russian Science Foundation grant 19-42-04133.
Gradients on the order of 1 GV/m have been obtained via single cycle (~1 ps) THz pulses produced by the conversion of a high peak power laser radiation in nonlinear crystals (~1 mJ, 1 ps, up to 3% conversion efficiency). For electron beam acceleration with such broadband (0.1- 5 THz) pulses, we propose arrays of parabolic focusing micro-mirrors with common central. To measure energy gain of electrons in the THz structure we propose applying a voltage (up to 400 kV) to the structure respecting the cathode and anode. Electrons become preliminary accelerated at the entrance that makes design of the structure simpler, because velocity of particles is near to be constant and almost equals the speed of light. On the other hand, the anode can be reached only by the electrons accelerated in the THz field so that one can directly measure the resulting energy gain at the anode.
 
poster icon Poster WEPP29 [1.112 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-WEPP29  
About • paper received ※ 01 September 2020       paper accepted ※ 27 October 2020       issue date ※ 30 October 2020  
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THAO01
Machine Learning-based Beam Size Stabilization  
 
  • S.C. Leemann
    LBNL, Berkeley, California, USA
 
  In state-of-the-art synchrotron light sources the overall source stability is presently limited by the achievable level of electron beam size stability. This source size stability is presently on the few-percent level, which is still 1-2 orders of magnitude larger than already demonstrated stability of source position/angle (slow/fast orbit feedbacks) and current (top-off injection). Until now, source size stabilization has been achieved through corrections based on a combination of static predetermined physics models and lengthy calibration measurements (feed-forward tables), periodically repeated to counteract drift in the accelerator and instrumentation. We now demonstrate for the first time [PRL 123 194801 (2019)], how application of machine learning allows for a physics- and model-independent stabilization of source size relying only on previously existing instrumentation in ALS. Such feed-forward correction based on neural networks that can be continuously online-retrained achieves source size stability as low as 0.2 microns rms (0.4%) which results in overall source stability approaching the sub-percent noise floor of the most sensitive experiments.  
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THAO02
Using Machine Learning Tools to Predict Accelerator Failure  
 
  • M. Reščič, R. Seviour
    University of Huddersfield, Huddersfield, United Kingdom
  • W. Blokland
    ORNL, Oak Ridge, Tennessee, USA
 
  Modern particle accelerator facilities are continuously introducing improved beam diagnostics, data acquisition, storage and analysis capabilities. Although the increased volume of data this generates makes manual analyse and understand the acquired data very difficult. In this paper we propose the use of machine learning to better understanding of beam failures. The proposed methods allow for both precognitive failure prediction and failure classification, determined using existing beam diagnostics infrastructure. Where we present the concept of tuning classifier parameters and pulse properties to refine datasets. As a demonstrator we apply our machine learning algorithm to analysis the vast data generated by the Oakridge Spallation Neutron Source (SNS) Differential Beam Current Monitoring (DBCM) diagnostics system. We show that analysis of the SNS DBCM data using machine learning, particle accelerator failure can be identified prior to the actual machine failure with 92% accuracy. Importantly, our research shows that emergent behavior regarding machine failure is encoded in the beam pulses prior to failure actually occurring.  
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THAO04 Beam Coupling Impedance Analyze Using Bunch-by-Bunch Measurement 202
 
  • X.Y. Xu
    University of Chinese Academy of Sciences, Beijing, People’s Republic of China
  • Y.B. Leng, X.Y. Xu
    SSRF, Shanghai, People’s Republic of China
  • X.Y. Xu
    SINAP, Shanghai, People’s Republic of China
 
  Beam coupling impedance is very important parameters for advanced synchrotron radiation facilities. Till now there is no online method to measure beam impedance directly. But some beam parameters such as betatron tune amplitude and frequency, synchrotron phase, bunch lifetime and so on, can be modulated by beam impedance effects. So wake field and beam impedance information could be retrieved by measuring bunch-by-bunch beam 3D positions and analyzing bunch index dependency of above beam parameters. A bunch-by-bunch 3D positions and charge measurement system had been built at SSRF for this purpose and the performance is not good enough for beam impedance analyze due to cross talk between bunches. We upgraded the measurement system to minimize cross talk and improve resolution this year. New beam experiment results and corresponding analyze will be introduced in this paper.  
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slides icon Slides THAO04 [1.340 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-THAO04  
About • paper received ※ 02 September 2020       paper accepted ※ 14 September 2020       issue date ※ 30 October 2020  
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THPP25 Measurements of Ion Instability and Emittance Growth for the APS-Upgrade 258
 
  • J.R. Calvey, M. Borland, T.K. Clute, J.C. Dooling, L. Emery, J. Gagliano, J.E. Hoyt, P.S. Kallakuri, L.H. Morrison, U. Wienands
    ANL, Lemont, Illinois, USA
 
  Ions are produced in an accelerator when the beam ionizes residual gas inside the vacuum chamber. If the beam is negatively charged, ions can become trapped in the beam’s potential, and their density will increase over time. Trapped ions can cause a variety of undesirable effects, including instability and emittance growth. Because of the challenging emittance and stability requirements of the APS-Upgrade storage ring, ion trapping is a serious concern. To study this effect at the present APS, a gas injection system was installed. A controlled pressure bump of Nitrogen gas was created over a 6m straight section, and the resulting ion instability was studied using several different detectors. Measurements were taken using a pinhole camera, spectrum analyzer, bunch-by-bunch feedback system, and a gas bremsstrahlung detector. Studies were done under a wide variety of beam conditions, and at different pressure bump amplitudes. In this paper we report on the results of some of these measurements, and discuss the implications for present and future electron storage rings.  
poster icon Poster THPP25 [0.761 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-THPP25  
About • paper received ※ 03 September 2020       paper accepted ※ 16 September 2020       issue date ※ 30 October 2020  
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THPP26 Transverse Broad-band Impedance Studies of the New In-vacuum Cryogenic Undulator at Bessy II Storage Ring 263
 
  • M. Huck, J. Bahrdt, H. Huck, A. Meseck, M. Ries
    HZB, Berlin, Germany
 
  The first radiation from the cryogenic permanent magnet undulator (CPMU17) has been observed in December 2018 at the BESSY II storage ring at HZB, and since then this device has served as a light source for beamline commissioning. It is the first in-vacuum undulator installed at BESSY II, and a new in-vacuum APPLE undulator (IVUE32) is planned to be installed in near future. Thus, a detailed study of the interactions between such an in-vacuum device and the electron beam is required. Beam-based measurements using orbit-bump and tune-shift methods have been applied to estimate the vertical impedance of CPMU17. For CPMU17 the first results of broad-band impedance studies are presented.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-THPP26  
About • paper received ※ 29 August 2020       paper accepted ※ 19 September 2020       issue date ※ 30 October 2020  
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THPP29 Application of Wavelet Algorithm in Tune Measurement 268
 
  • X. Yang
    SINAP, Shanghai, People’s Republic of China
  • F.Z. Chen, L.W. Lai
    SSRF, Shanghai, People’s Republic of China
  • X. Yang
    UCAS, Beijing, People’s Republic of China
 
  Tune is a very important parameter for storage ring of advanced synchrotron radiation facilities. At present, fast Fourier transform (FFT) is the core algorithm of the beam spectrum analysis used in tune measurement. Taking into account the nonlinear effect in the accelerator, tune changes during the process of storage ring injection and booster energy upgrading. However, the Fourier method is used to analyse the global sampling point, and the ability to distinguish the local variation of the tune in the sampling time is poor. This paper leads wavelet analysis method as the core algorithm into beam spectrum analy-sis method, further analyses the change of the tune with beam amplitude in sampling time, and compares this new algorithm with the traditional Fourier method. New ex-perimental results and corresponding analysis for the data from SSRF will be introduced in this paper.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2020-THPP29  
About • paper received ※ 02 September 2020       paper accepted ※ 18 September 2020       issue date ※ 30 October 2020  
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