Identification of Imperfections in Impedance Shields on the SPS-QF Flanges via Non-Intrusive Measurements

In order to achieve the highest beam intensities possible in the LHC the highest quality beam possible has to be supplied by the injector chain. The Super Proton Synchrotron (SPS) at CERN is the last accelerator in the injector chain of the LHC. One factor that is currently known to limit the intensity of the beam for injection to the LHC, is the longitudinal beam-coupling impedance in the SPS. One known source of multi-bunch instability is the vacuum flanges and campaigns to mechanically shield this source were completed in the year 2000. However, today it cannot be excluded that some of these shields may have partial or indeed full failures. Since these flanges are next to a QF magnet and are in most cases connected to a BPH (Beam Position Monitor Horizontal), it is possible to carry out via the BPH an in-situ measurement of the effectiveness of the shields. In this paper we present a methodology as well as measurement results taken with this non-intrusive in-situ method. From measurements, it is possible to identify if the flanges are without any impedance shield, equipped with either a fully functioning shield or a shield exhibiting non-ideal properties.