Author: Novokshonov, A.I.
Paper Title Page
TUPP011 Observation of Scintillators Charging Effects at the European XFEL 308
 
  • A.I. Novokshonov, B. Beutner, G. Kube
    DESY, Hamburg, Germany
  • S.A. Strokov
    TPU, Tomsk, Russia
  
  Scintillating screens are widely used for beam profile diagnostics at various kinds of particle accelerators. At modern linac based electron machines with ultrashort bunches as the European XFEL in Hamburg (Germany), scintillators help to overcome the limitation of standard OTR based monitors imposed by the emission of coherent radiation. The XFEL injector section is equipped with four off-axis screens allowing to perform online beam profile diagnostics, i.e. a single bunch out of a bunch train is kicked onto the screen and the profile is analyzed. However, during user operation a decrease of the SASE level was observed in cases that one of the of-axis screens was used. The observation is explained by charging of the scintillator screen: each deflected bunch hitting the screens causes ionization and charging of the screen. The scintillator as good insulator keeps the charge for some time such that the non-deflected part of the bunch-train feels their Coulomb force and experiences a kick, resulting in a drop of the SASE level. This report summarizes the observations at the European XFEL and introduces a simple model for quantification of this effect.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-TUPP011  
About • paper received ※ 04 September 2019       paper accepted ※ 07 September 2019       issue date ※ 10 November 2019  
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TUPP012 Image of the Transverse Bunch Profile via COTR 313
 
  • A. Potylitsyn, T. Gusvitskii, L.G. Sukhikh
    TPU, Tomsk, Russia
  • G. Kube, A.I. Novokshonov
    DESY, Hamburg, Germany
  
  Funding: This work was supported by the grant of the Russian Ministry of Science # 3/1903.2017.
Transverse beam profile diagnostics based on Optical Transition Radiation (OTR) is a routine technique at most modern electron linear accelerators (linacs) which is difficult to implement for FEL beams [*] and LWPA accelerators [**]. The reason is that a standard OTR beam profile monitor with a few micrometers space resolution cannot be used for measurements of ultrashort bunch profiles due to coherent effects in the OTR emission process [***]. We have developed an approach which allows calculating the propagation of coherent optical transition radiation (COTR) through a standard optical system consisting of a focusing lens and a spatial resolving detector placed in the image plane. Strict summation of the OTR fields emitted coherently by electrons inside the bunch and its focusing onto the detector plane allows obtaining a COTR image of the bunch profile. With the assumption of a Gaussian transverse bunch profile it is shown that the resulting image has a typical "ring" shape, characteristics of which are depended on the bunch transverse rms size and optical system parameters.
* E. Saldin, et al., "The Physics of Free Electron Lasers", Springer-Verlag, 2010.
** N. Bourgeois, et al., AIP Conf. Proc., 1507, 258 (2012).
*** H. Loos, R. Akre, et al., SLAC-PUB-13395 (2008). 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-TUPP012  
About • paper received ※ 04 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)