Electron Cloud Measurements of Coated and Uncoated Vacuum Chambers in the CERN SPS by Means of the Microwave Transmission Method

Electron cloud is a limitation to increasing the beam current in the CERN SPS in the frame of an intensity upgrade of the LHC complex. Coating the vacuum chamber with a thin amorphous carbon layer is expected to reduce the electron cloud build-up. Three SPS MBB magnets have been coated to study the performance of this carbon coating. The microwave transmission method is one possible way to monitor electron cloud and hence to test the effect of the coating. In this paper the evolution of the experimental setup for measurements of the electron cloud using LHC type beams will be described. Due to the low revolution frequency of about 43 kHz serious electromagnetic compatibility problems as well as intermodulation have been found. These effects and their mitigation are described. Finally, we present the measurement results illustrating the possible reduction due to the carbon coating.