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TY - CONF AU - Shaposhnikova, E.N. AU - Argyropoulos, T. AU - Bohl, T. AU - Campelo, J.V. AU - Caspers, F. AU - Esteban Müller, J.F. AU - Lasheen, A. AU - Salvant, B. AU - Timko, H. ED - Petit-Jean-Genaz, Christine ED - Arduini, Gianluigi ED - Michel, Peter ED - Schaa, Volker RW TI - Identification of High-frequency Resonant Impedance in the CERN SPS J2 - Proc. of IPAC2014, Dresden, Germany, June 15-20, 2014 C1 - Dresden, Germany T2 - International Particle Accelerator Conference T3 - 5 LA - english AB - The spectrum of long bunches injected into the ring with RF switched off has been used in the SPS in the past to probe the longitudinal coupling impedance. After a large campaign of shielding of 800 inter-magnet vacuum ports in 1999 - 2001, the microwave instability threshold was significantly increased and the high-frequency spectrum of the beam became practically flat, apart from a prominent peak at around 1.4 GHz. As corresponding high-frequency impedance could potentially lead to microwave instability of high intensity bunches observed now at high energies in the SPS, a search of the source of this impedance was launched. Using a combination of impedance simulations and measurements, vacuum flanges that are present in a large quantity in the machine have been identified as a main source of impedance at this frequency. Particle simulations based on the SPS impedance model, which includes this previously unknown impedance, are able to reproduce the characteristics of the bunch spectrum and amplitude growth rates and hence, confirm that the impedance of the vacuum flanges is responsible for the observed spectral peak. PB - JACoW CP - Geneva, Switzerland SP - 1416 EP - 1418 KW - impedance KW - simulation KW - vacuum KW - damping KW - resonance DA - 2014/07 PY - 2014 SN - 978-3-95450-132-8 DO - 10.18429/JACoW-IPAC2014-TUPME029 UR - http://jacow.org/ipac2014/papers/tupme029.pdf ER -