EVALUATION OF THE BEAM-COUPLING IMPEDANCES OF THE DA-PHI-NE CAVITY - NUMERICAL AND ANALYTICAL RESULTS

Waveguide dampers are going to be widely used in accelerator RF caviti es to reduce the beam-coupling impedances at the frequency of the high er order modes. in order to avoid multi-bunch instabilities. The numer ical evaluation of the beam-coupling impedances in cavities equipped w ith waveguide dampers leads to the solution of a 3D held problem, that requires a vast amount of computing time on powerful computers. In th is paper we present a simple analytical method, based on the well-know n Kirchhoff approximation, that permits an evaluation of the coupling between the cavity and the waveguide modes, thus yielding a first esti mate of the e-factors of the damped modes. We also discuss the evaluat ion of the damping effect in the case of the DA Phi NE RF cavity throu gh the post-processing of the data from a 3D code. The results of the two approaches are compared, and checked against experimental results and other numerical simulations.