Experimental Study of the Electron Cloud Instability at the CERN SPS

The electron cloud instability limits the performance of many existing proton and positron rings. A simulation study carried out with the HEADTAIL code revealed that the threshold for its onset decreases with increasing beam energy, if the 6D emittance of the bunch is kept constant and the longitudinal matching to the bucket is preserved. Experiments have been carried out at the CERN-SPS to study the dependence of the vertical electron cloud instability on the energy and on the beam size. The reduction of the physical transverse emittance as a function of energy is considered in fact to be the main reason for the unusual dependence of this instability on energy.