Measurements of coherent tune shift and head-tail growth rates at the SPS

Measurements of the coherent tune shifts with intensity and of head-tail growth rates have been performed with single proton bunches in the SPS, at 26 Gev. From these measurements, the real and imaginary part of the transverse impedance can be estimated. Together with earlier and future measurements, this will be used to experimentally document and follow up the effect of the impedance improvements on the SPS as injector for the LHC. A reproducibility at the 20% level was achieved for the value of the effective vertical impedance inferred from the coherent tune-shit measurements.