Design of the R.T. CH-Cavity and Perspectives for a New GSI Proton Linac

The CH-Structure has been studied at the IAP Frankfurt and at GSI for several years. Compared with the IH structure (H110-mode), the CH structure (H210-mode) can work at higher frequency (700 MHz) and can accelerate ions to higher energy (up to 150 AMeV). Detailed Microwave Studio (MWS) simulations were performed for this structure. Since a multi-gap cavity can be approximated as a quasi-periodic structure, it is possible to analyze one βλ/2-cell at an energy corresponding to the cavity center. Additionally, a reduced copper conductivity of 85% was assumed. Geometry variations with respect to rf frequency and shunt impedance can be performed rapidly by that method in the first stage of optimization. Effective shunt impedances from 100 MΩ/m down to 25 MΩ/m were obtained for the energy range from 5 AMeV to 150 AMeV by this method. The rf frequency was 350 MHz up to 70 MeV and 700 MHz above. A systematic analysis of the influence of the cell number in long CH cavities on the effective shunt impedance is presented. The possibility to apply this structure to a 70 mA, 70 MeV, 352 MHz proton linac for GSI is discussed.