Single Bunch Transverse Intensity Limitations in the SPS

Single bunch intensities of 1.15 × 1011 protons will be required for the nominal, and 1.7 × 1011 protons for ultimate beams in the LHC. These intensities are at the limit of transverse beam stability at injection energy into the SPS and can lead to very fast transverse instabilities that have recently been observed. There has been a major effort to reduce the SPS impedance. We describe and review the results of transverse beam measurements performed in the SPS. This includes transverse impedance measurements based on coherent tune shifts and measurements of growth and decay rates of several head tail modes as function of chromaticity. We also comment on the effect of the flat chamber geometry.