Development of a coupled CH structure for the GSI proton injector

The FAIR facility, under development at GSI, needs a new dedicated proton injector for the production of intense secondary p macr beams. This injector will accelerate protons from 3 to 70 MeV at a current of 70 mA, and due to the high voltage gain and shunt impedance will be based on CH cavities powered by 6 2.5 MW, 325 MHz klystrons. An innovative coupling cell containing one drift tube of length Nbetalambda was developed to combine multicell drift tube modules of the CH-type (H ₂₁₁ mode). In order to study this coupling mechanism a 1:2 scaled model of the second resonator of GSI proton injector was fabricated at IAP and it ready for testing. The according full scale prototype, a 3 meter long coupled resonator from 11.7 MeV to 24.1 MeV is under development and will be power tested with a 2.5 MW klystron at GSI early in 2009. This paper describes in detail the coupled structure together with a general overview of the R&D results achieved on the CH-DTL´s cavity.