Keyword: HOM
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TUPB07 Stability Study of Beam Position Measurement Based on Higher Order Mode Signals at FLASH cavity, dipole, electron, higher-order-mode 273
 
  • J.H. Wei
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • N. Baboi
    DESY, Hamburg, Germany
  • L. Shi
    PSI, Villigen PSI, Switzerland
 
  FLASH is a free-electron laser driven by a supercon-ducting linac at DESY in Hamburg. It generates high-brilliance XUV and soft X-ray pulses by SASE (Self Amplified Spontaneous Emission). Many accelerating cavities are equipped with HOMBPMs (Higher Order Mode based Beam Position Monitors) to align the beam and monitor the transverse beam position. However, these lose their position prediction ability over time. In this paper, we applied an efficient measurement and signal analysis with various data process methods including PLS (Partial Least Square) and SVD (Singular Value Decomposition) to determine the transverse beam position. By fitting the HOM signals with a genetic algorithm, we implemented a new HOMBPM calibration procedure and obtained reliable beam prediction positions over a long time. A stable RMS error of about 0.2 mm by using the spectra of signals and 0.15 mm by using the new method over two months has been observed.  
poster icon Poster TUPB07 [1.816 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-TUPB07  
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TUPC11 Design of an Ultrafast Stripline Kicker for Bunch-by-Bunch Feedback kicker, FEL, impedance, electron 322
 
  • J. Wang, P. Li, D. Wu, D.X. Xiao, L.G. Yan
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
 
  Funding: Work supported by China National Key Scientific Instrument and Equipment Development Project (2011YQ130018), National Natural Science Foundation of China (11475159, 11505173, 11575264 and 11605190)
The CAEP THz Free Electron Laser (CTFEL) will have a fast transverse bunch-by-bunch feedback system on its test beamline, which is used to correct the beam position differences of individual bunches with interval of about 2 ns. In this paper, we are proposing an ultrafast wideband stripline kicker, which is able to provide a kick to the bunch in a 2 ns time window. The structure design and simulation results of this kicker are also discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-TUPC11  
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WEOC04 Space Charge Effects Studies for the ESS Cold Linac Beam Profiler space-charge, electron, simulation, proton 371
 
  • F. Belloni, F. Benedetti, G. Coulloux
    CEA/DRF/IRFU, Gif-sur-Yvette, France
  • P. Abbon, F. Gougnaud, C. Lahonde-Hamdoun, P. Le Bourlout, Y. Mariette, J. Marroncle, J.-Ph. Mols, V. Nadot, L. Scola
    CEA/DSM/IRFU, France
  • C.A. Thomas
    ESS, Lund, Sweden
 
  Five Ionization Profile Monitors are being built by CEA in the framework of the in-kind contribution agreement signed with ESS. The IPMs will be installed in the Cold Linac where the proton energy range they need to cover extends from 90 MeV to 2 GeV. The ESS fields intensity of 1.10+09 protons/bunch delivered at a frequency of 352 or 704 MHz, with a duty cycle of 4%, may strongly affect the trajectories of the ionized molecules and electrons created by the passage of the beam through the residual gas. In order to quantify and to develop a correction algorithm for these space charge effects, a code was initiated at ESS and completed at CEA Saclay with the possibility to include real case electric fields calculated with Comsol Multiphysics. A general overview of the code and its preliminary results are presented here.  
slides icon Slides WEOC04 [5.186 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEOC04  
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WEPA09 Long Term Beam Phase Monitoring Based on HOM Signals in SC Cavities at FLASH cavity, controls, electron, FEL 388
 
  • J.H. Wei
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • N. Baboi
    DESY, Hamburg, Germany
  • L. Shi
    PSI, Villigen PSI, Switzerland
 
  The accelerating RF fields in superconducting cavities must be controlled precisely in FEL (Free Electron Laser) facilities to avoid beam energy spread and arrival time jitter. Otherwise the beam quality is degraded. The LLRF (Low Level Radio Frequency) system controls the RF field and provides a highly stable RF reference. A new type of beam phase determination technique based on beam-excited HOMs (Higher Order Modes) in cavities has been implemented. The two special couplers installed at both ends of each cavity, pick up the signals containing both the leakage of the accelerating field and the HOM signals. Therefore the signals can be used to calculate the beam phase directly with respect to the RF phase. We analysed the factors which may affect the result of the beam phase on a long-term based on an experimental platform at FLASH. Some phase drifts between the HOM-BPhM (Beam Phase Monitor) and the LLRF system phase measurement were observed and the reason will be further studied.  
poster icon Poster WEPA09 [1.720 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA09  
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WEPB04 Comparison of YAG Screens and LYSO Screens at PITZ electron, emittance, laser, background 438
 
  • R. Niemczyk, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, F. Stephan, Q.T. Zhao
    DESY Zeuthen, Zeuthen, Germany
  • W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
 
  The Photo Injector Test facility at DESY in Zeuthen (PITZ) is dedicated to the development of high-brightness electron sources for free-electron lasers. At PITZ, to measure the emittance of space-charge-dominated beams, the slit scan technique is used. For slice emittance measurements a transverse deflecting structure (TDS) is employed. The electron beam distribution is measured by means of scintillator screens. Both the TDS and the slit mask reduce the signal strength, giving stringent requirements on the sensitivity of the screens. At PITZ, high-sensitivity Ce:LYSO screens have been installed at the same screen stations as the standard Ce:YAG screens to solve low-intensity issues. A comparison of both screens is presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPB04  
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WEPB12 Design and Implementation of Non-Invasive Profile Monitors for the ESS LEBT instrumentation, ion-source, beam-transport, simulation 455
 
  • C.A. Thomas, T.J. Grandsaert, H. Kocevar, Ø. Midttun, N. Milas, R. Miyamoto, T.J. Shea
    ESS, Lund, Sweden
 
  Non-invasive Profile Monitors are designed and distributed along the ESS Linac. In the Low Energy Beam Transport (LEBT), a specific one has been designed to be primarily a beam position monitor. Its main requirement is to measure the beam position with 100µm accuracy, and in addition it provides the beam profile and size. This performance have been shown to be possible and remains to be demonstrated experimentally. The instrument is also potentially capable of measuring the angle of the beam and its divergence. In this paper we will study the accuracy of such a measurement as function of the instrument image quality.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPB12  
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