Electron beam dynamics in the CERN PS

The 28 GeV proton synchrotron (PS) forms part of the chain of LEP injectors with the role of accelerating positrons and electrons from 0.6 GeV, the operating energy of the Electron/Positron Accumulator (EPA), to 3.5 GeV, the positron/electron injection energy of CERN's 400 GeV proton synchrotron (SPS) which then accelerates the particle to 20 GeV. Bunch length and energy spread must be chosen carefully to avoid transverse and longitudinal single-bunch instabilities associated with high peak currents in the SPS. An analysis of the beam dynamics in the combined function lattice of the PS shows that this requirement can be fulfilled if the damping-partition numbers are changed. A Robinson Wiggler is proposed for this purpose and a new additional RF system is needed to produce the required bunch dimensions in the longitudinal phase space. In this paper, the required dimensions, including the maximum bunch length, the relative rms energy spread, and the maximum transverse emittance, are derived. Two approaches are proposed for obtaining the proper bunch dimensions: bunch expansion or bunch-length compression