Optimisation of accelerator reliability for ADS: Example of SC cavities and the associated RF power couplers

In order to limit as much as possible the number of thermal shocks in the spallation target and the reactor core, ADS-class accelerators require an extremely high reliability of less then 5 beam-trips per year. The recent European (FP5) Study PDS-XADS has established the following to be the main parameters for reliable accelerator operation: use of derated and redundant components, intrinsic fault tolerance and a dedicated maintenance strategy. In this paper the progress of certain aspects of reliability studies done at the Institute of Nuclear Physics in Orsay will be presented. The low level RF fast feedback system for the SC cavities operation, providing the necessary beam stability, will be discussed. Also the conceptional design of the RF power coupler that requires a high level of robustness is given. (author)