Report on Superconducting RF Activities at CERN from 2001 to 2003

The main project on superconducting RF at CERN in the period from 2001 to 2003 has been the 400 MHz SC system for the LHC. Five modules, each containing four single-cell niobium (Nb) sputtered cavities, have been assembled and low-power tested at room temperature and at 4.5 K. Production of the first four power couplers has been delayed but high-power tests should start on the first module this autumn. A small program of R&D is maintained on the SPL. Both the beta = 0.7 and beta = 0.8 cavities have been high-power tested up to nominal field without particular problems. A detailed characterization of the cavity mechanical resonances is going on and some preliminary results are presented. A computer code has been written to predict the effects of Lorentz detuning and microphonics on the stability of the RF feedback loops in SC linacs where several cavities are driven by a single high power source. Fast ferrite phase shifters are being developed to allow the decoupling of the feedback loops of individual cavities attached to the same klystron. Several collaborations, e.g. SOLEIL, PACO and S3HC, have successfully achieved their objectives. The collaboration established with Cornell to develop a 200 MHz SC cavity has not yet led to the desired level of performance. The R&D program on 1.5 GHz is continuing. Based on an optimised electropolishing process for surface preparation, the study is at present focused on the effect of Hydrogen (H2) on the Nb films' RF performance.