CERN, Geneva
Controlled longitudinal emittance blow-up together with a fourth harmonic RF system are two techniques that are being used in the SPS in order to stabilize the beam before injecting into the LHC. The emittance blow-up has been achieved by introducing a band-limited phase noise during acceleration. Measured variations of the final emittance along the batch can be explained by the modification of the synchrotron frequency distribution due to the effect of beam loading in a double harmonic RF system.
CERN, Geneva
The peak detected Schottky spectrum is used for beam observation in the CERN SPS and now already in the LHC. This tool was always believed, however without proof, to give a good picture of the particle distribution in synchrotron frequencies similar to the longitudinal Schottky spectrum of unbunched beam for revolution frequencies. The analysis shows that for an optimised experimental set-up the spectrum of the peak detected signal is very close to the synchrotron frequency distribution inside the bunch - much closer than that given by the traditional longitudinal bunched-beam Schottky spectrum. The limitations of the present experimental set-up in the SPS are discussed together with possible improvements.
