The CERN ps as e+e- accelerator in the LEP injector chain: First results

The role of the 28 GeV Proton Synchrotron (PS) in the LEP injector chain (1) is to accelerate up to 3.5 GeV and transfer to the SPS e+ and e- delivered by the Electron Positron Accumulator (EPA) at 600 MeV. First injection in the PS of e- at 500 MeV and acceleration was achieved, as scheduled, in September 1986. As required by future operation, these first tests were carried out while delivering beams of different particles to the other PS users. Two different modes of acceleration and bunch shaping needed for stability at injection in SPS have been successfully tried up to twice the nominal intensity: 1) with two new high Q 114 MHz cavities (2) (''Bunch Expansion''), 2) with the existing ferrite cavities tuned at 3.8 MHz and one new high Q 114 MHz cavity (''Long Bunch Expansion''). As a consequence of the combined function magnets in the PS, the longitudinal and horizontal damping partition numbers are Je = 4 and Jx =-1 respectively, therefore electron acceleration is horizontally unstable. Because of this, in all three modes the damping partition numbers, and thus longitudinal and horizontal beam emittance, were controlled by Robinson wigglers. Synchrotron radiation effects were also studied during a dedicated run. This paper describes the problems encountered and the performance achieved so far