Design and electromagnetic analysis of the new DAFNE interaction region

A new interaction region (IR) vacuum chamber has been designed for the DAFNE upgrade aimed at testing of the crabbed waist collision scheme. Compared to the existing IR vacuum chamber, the new one has a simplified design and consists essentially of the confluence of straight tubes, having a double Y shape. Sharp discontinuities have been avoided to limit the beam impedance of the structure. However, the study of the electromagnetic interaction with the beam is necessary in order to avoid excessive power loss due to possible higher order modes (HOM) trapped in the Y-shape chamber. The first design of the chamber has been analyzed with HFSS and HOMs have been found and characterized. On the basis of these results some modifications in the geometry of the IR chamber have been introduced to eliminate or attenuate these trapped resonances. The results of these simulations are presented. New electromagnetic shielding for the bellows inserted in the IR chambers, have been developed as well. The design criteria and the simulation results for these shielded bellows are also reported.