Radio-Frequency Multipacting as Quality Control of Coatings for E-Cloud Suppression

To mitigate electron cloud in particle accelerators a carbon coating with low SEY (Secondary Electron Yield) has been developed. In the case of the SPS (Super Proton Synchrotron), which belongs to the LHC injector chain, testing of the performance of coated beam pipes directly in the accelerator must cope with the schedule of the regular machine operation. For this reason an alternative tool based on RF induced multipacting in a coaxial configuration has been designed for ex-situ characterization of the main bending dipoles of the SPS. In this contribution we report the results obtained before and after coating for two 6.4 meter dipoles with different cross sections of the vacuum chambers. The multipacting is monitored by measuring the pressure rise and the RF reflected power. After coating, the power threshold to induce multipacting is strongly reduced indicating a lower propensity for electron cloud. The impact of the RF coupling on the sensitivity of the technique is discussed.