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TY - CONF AU - Schneider, M. AU - Adelmann, A. AU - Pogue, N. AU - Stingelin, L. ED - Chrin, Jan ED - Schaa, Volker RW TI - Suppression of RF Radiation Originating from the Flattop Cavity in the PSI Ring Cyclotron J2 - Proc. of Cyclotrons2016, Zurich, Switzerland, September 11-16, 2016 C1 - Zurich, Switzerland T2 - International Conference on Cyclotrons and Their Applications T3 - 21 LA - english AB - In the PSI Ring cyclotron, protons are accelerated from 72 MeV to 590 MeV. In several upgrade programs, the beam current was increased from the initial design value of 100 μA up to 2.4 mA. The rf-system of this separated sector cyclotron consists of 4 copper cavities running at 50 MHz for the main acceleration. For the purpose of increasing the phase acceptance of the Ring, an aluminum flattop cavity is operated at a gap voltage of 555 kVp at the 3rd harmonic frequency. As a result of the progressively increased flattop voltage, this cavity was pushed toward its mechanical and electrical limits. As a consequence rf-power is leaking into the cyclotrons vacuum chamber, which in turn caused several problems. A visible effect was the formation of plasma in the vacuum chamber *. In the last shutdown, an attempt was made to reduce the radiated rf-power. On the vacuum sealing between the flattop cavity and sector magnet 6, a shim was installed which reduces the gap for the beam from 60mm to 25mm in height. Results of this intervention will be presented and compared with finite element model simulations **. PB - JACoW CP - Geneva, Switzerland SP - 348 EP - 350 KW - cavity KW - flattop KW - vacuum KW - cyclotron KW - pick-up DA - 2017/01 PY - 2017 SN - 978-3-95450-167-0 DO - 10.18429/JACoW-Cyclotrons2016-THP18 UR - http://jacow.org/cyclotrons2016/papers/thp18.pdf ER -