Simulation of single bunch instabilities driven by electron cloud in the SPS

Photoemission, or gas ionization, and secondary emission can give rise to a quasi-stationary electron cloud inside the beam pipe through a beam-induced multipacting process. We investigate single bunch instabilities driven by a quasi-stationary electron cloud by means of a computer simulation. The model that we apply makes use of two sets of macroparticles for both the bunch particles and for the electrons, which interact at one or more locations along the beam orbit. Two different schemes have been implemented for the electron cloud field calculation (PIC and soft-Gaussian), and their efficiencies are compared. The code is used to simulate possible instability mechanisms in the SPS. The options of a broad-band wake-field and space charge includuced tune spread have ben also introduced in order to follow the bunch evolution under the combined effect of the elctron-cloud and a broad-band impedance