Kube, G. Liu, S. Novokshonov, A.I. Scholz, M. JACoW Publishing Geneva, Switzerland 978-3-95450-201-1 10.18429/JACoW-IBIC2018-WEOC03 English 366-370 WEOC03 FEL electron diagnostics scattering ECR Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-IBIC2018-WEOC03 http://jacow.org/ibic2018/papers/weoc03.pdf Standard beam profile measurements of high-brightness electron beams based on OTR may be hampered by coherence effects. Therefore it was decided for the European XFEL to measure transverse beam profiles based on scintillating screen monitors using LYSO:Ce. While it is possible to resolve beam sizes down to a few micrometers with this scintillator, the experience during the XFEL commissioning showed that the measured emittance values were significantly larger than the expected ones. In addition, beam profiles measured at bunch charges of a few hundred pC showed a ’smoke ring’ structure. While coherent OTR emission and beam dynamical influence can be excluded, it is assumed that the profile distortions are caused by effects from the scintillator material. Following the experience in high energy physics, a simple model was developed which takes into account quenching effects of excitonic carriers inside a scintillator in a heuristic way. Based on this model, the observed beam profiles can be understood qualitatively. Together with the model description, first comparisons with experiments will be presented, and new scintillators suitable for beam profile diagnostics will be discussed.