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TY - CONF AU - Lipka, D. AU - Lorbeer, B. ED - Schaa, Volker RW ED - Jansson, Andreas ED - Shea, Thomas ED - Olander, Johan TI - Pile-Up Effect of Cold Button BPMs in the European XFEL Accelerator J2 - Proc. of IBIC2019, Malmö, Sweden, 08-12 September 2019 CY - Malmö, Sweden T2 - International Beam Instrumentation Conferenc T3 - 8 LA - english AB - The European XFEL facility is in operation with a maximum of 2700 bunches in one train. The highest bunch repetition rate is 4.5 MHz; this corresponds to a minimum time separation of 222 ns. The measurement of the beam properties for each bunch in a train is required. Therefore the beam position monitor (BPM) system needs to separate the signals from each bunch. All BPM types (button, re-entrant and cavity) fulfill this requirement except a few button BPMs installed inside of the cold accelerator module, where Pile-Up from the train can be observed. To identify the cause of this effect we measured the S-parameters during a shutdown of the accelerator, compared it with a similar BPM at the FLASH accelerator but located in a warm section and finally measured the spectrum of the button signal during beam operation. As a result, resonances were found at about 2.46 GHz with relatively high quality factor that remains within the frequency range accepted by the electronics. PB - JACoW Publishing CP - Geneva, Switzerland SP - 453 EP - 456 KW - resonance KW - cavity KW - FEL KW - electron KW - electronics DA - 2019/11 PY - 2019 SN - 2673-5350 SN - 978-3-95450-204-2 DO - doi:10.18429/JACoW-IBIC2019-WEAO02 UR - http://jacow.org/ibic2019/papers/weao02.pdf ER -