Coupling Methods for Superconducting CH-Cavities

The cross-bar H-type (CH) cavity is a multi-gap drift tube structure based on the H-210 mode currently under development at IAP Frankfurt [1]. Based on detailed numerical simulations a 19 cell prototype cavity from massive Niobium was realized. Experimental investigations have started already. With respect to rf coupling inductive coupling was applied successfully for cavity rf conditioning at room temperature with power levels up to 2 kW. Capacitive coupling through the girder is however preferred in case of sc operation. Recent investigations led to a modified cavity geometry which allows to integrate a capacitive power coupler with Qevalues down to 10⁶in future CH-cavities. Main consequences on the cavity are significantly lower and broader girder profiles as well as simplified stem geometries (round instead of elliptical stem bases). These modifications will provide space for power couplers through the girders. Additionally, the cavity stiffness against vacuum forces is improved by these modifications.