Beam Characteristics versus Cavity Models in Clic

The luminosity requested for linear colliders with centerof-mass energies exceeding 500 GeV, implies a multibunch operation be considered in order to limit the RF power consumption. In the Compact Linear Collider (CLIC), though the repetition rate is high, a train of at least 20 bunches is necessary to obtain the performance needed for the experiments. Since at high RF frequency the wakefields are large, beam break-up is critical and stability simulations have been carried out for different pre-estimated models of detuned and/or damped cavities. The results obtained give indications about the wakefield level that should not be exceeded along the train, to avoid significant emittance growth. They also show the sensitivity to some specific parameters and the dependence on the scaling of focusing with energy. Eventually, they are used as guide lines for accelerating structure development and as a basis for a possible set of CLIC parameters.