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 nu-merical simulations a 19 cell prototype cavity from mas-sive Niobium was realized. Experimental investigations have started already. With respect to rf coupling induc-tive coupling was applied successfully for cavity rf con-ditioning at room temperature with power levels up to 2 kW. Capacitive coupling through the girder is however pre-ferred in case of sc operation. Recent investigations led to a modified cavity geometry which allows to integrate a capacitive power coupler with Qe values down to 106 in 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 stiff-ness against vacuum forces is improved by these modifica-tions. SUPERCONDUCTING (SC) CH-PROTOTYPE In sc cavities there is no cooling problem as in cw oper-ated rt (room temperatur) linacs. In general, sc linacs can be operated at higher gradients above a certain duty factor. Figure 1: The sc 352 MHZ CH prototype On the other hand, at low duty factors and high beam currents rt structures are very favourable because they are less expensive and can tolerate dark current contributions. ∗Supported by GSI Darmstadt, EU and by BMBF, contr. no. 06F134I To demonstrate the capabilites of the CH-DTL, it is fore-seen to test an sc CH cavity prototype. A design and engi-neering study has been performed in close cooperation with industry1. This study showed the feasibility of the produc-tion of superconducting CH cavities. The cavity production started in 2003; the completed cavity was delivered in April 2005 [2]. frequency [MHz] 35