Transverse Rigid Dipole and Intra-Bunch Oscillation Detection Using the Transverse Feedback Beam Position Detection Scheme in SPS and LHC

The LHC and SPS transverse dampers use beam position electronics with I,Q detection at 400 MHz and 200 MHz, of the sum and difference signals from a strip-line pick-up. Digitization is performed to give synchronous bunch-by-bunch data at the rate of 40 MHz corresponding to the bunch spacing of 25 ns. A performance in the um range is achieved with beams in LHC and has contributed to the high performance of the essential transverse feedback during the LHC run 1. In the present paper we review the systems deployed and their performance as well as the potential of the I,Q detection to also detect intra-bunch motion. The principle is illustrated using data from the LHC scrubbing runs in which intra-bunch motion is expected and has been observed due to electron cloud instabilities. The potential use of this signal to drive a transverse intra-bunch feedback system is outlined.