APPROACHING TO A MONO-MODAL ACCELERATING CAVITY BASED ON PHOTONIC BAND-GAP CONCEPTS

One of the main problem of high intensity accelerators is the presence of higher order modes (HOMs) which might degrade the beam quality. Accelerating cavities require HOMs suppression whereas keeping a high quality factor (Q) for the fundamental mode. Both these requirements can be hardly met in closed metallic cavities. At low frequency and for particular geometries it is possible to partially suppress HOMs. At high frequency and for superconducting cavities these configurations become cumbersome and technically unviable. We propose here a high Q cavity based on Photonic Band Gap (PBG) concepts, operating in the microwave region [1,2]. This cavity is intrinsically quasi-monomodal: HOMs can be efficiently suppressed without affecting the fundamental mode. We will present the study, the optimisation and the measurements of our metallic (Copper) PBG structure working in the 0.5-20 GHz range. Studies on different configurations working in the same frequency band are also discussed for room and low temperature measurements. The prototype of a hybrid metallic-dielectric PBG cavity will be presented too.