FACILITY AT THE SPS

The CERN SPS multiturn facility, based on the new beam orbit measurement system MOPOS, enables the User to ac-quire the position of the beam at each beam position mon-itor (BPM) over a number of consecutive turns. When the multiturn acquisition is synchronised with a perturbation imposed on the beam (for instance a fast kick), useful in-formation about the optics of the SPS and the dynamic be-haviour of the beam can be extracted from the data. A mea-surement of the amplitude and phase of the betatron oscil-lation at each BPM can be used to compare the theoretical optics functions with the real ones, and possibly to detect localised errors. Differences between two such measure-ments can be used to study the dependence on a variable pa-rameter (e.g. beam intensity, beam energy, etc.) and there-fore indirectly measure quantities, like the impedance, dis-tributed along the ring. Finally, due to the 90 degrees phase advance lattice, plotting the positions measured at two con-secutive BPMs against each other gives information about the behaviour of the beam in the transverse phase space. Results of measurements performed at the CERN SPS are presented