Hollow-core electromagnetic band gap waveguide as DC-break for ion sources

摘要

In order to allow beam extraction, microwave-based ion sources are usually located at high voltages. The RF link between the ion source plasma chamber and the microwave generators, placed at ground, needs to accomplish two basic functions: microwaves should be efficiently transferred to the plasma chamber and no DC-path must exist between the ion source and the RF power generator; moreover any dielectric breakdown due to the electrostatic fields must be avoided. This paper presents the study and design of an EBG hollow-core structure with a triangular lattice of air columns in Teflon, that accomplish both functions since is capable to handle a maximum microwave power of 1.5 kW and to fulfill a DC insulation up to 50 kV as requested in typical setups. The proposed structure consists in a photonic crystal hollow-core slab that can be directly coupled with two standard metallic waveguides. Such device confines and guides the electromagnetic field along the circular defect and could be capable to provide a low insertion loss as well as a break for DC path. With respect to the classical DC-break arranged as a multilayer of conductors and insulators, this innovative solution overcomes the drawbacks especially in terms of microwave leakage due to finite discontinuity between waveguides and dielectrics and reduces the high costs for the classical solution manufacture.