Summary of the production of the ACN cavities

The LHC-ACN RF system consists of eight normal conducting cavities (four per beam) made of bulk copper and resonating at 200.4 MHz. CERN provided the forged copper parts to the contractor for the final machining and assembly (Ettore Zanon S.p.A., based in Schio, Italy). The contractor had to weld all the flanges to the body of the cavity, machine and weld the cooling channels, carry out the final machining to have the right geometry and the requested RF surface finish, and make the final assembly of all the components by electron beam welding. The precision required during the various steps is quite tight with respect to the dimension of the cavities and would have required a very time-consuming and costly quality check during production, with the constant presence of a CERN staff member at the contractor's and subcontractor's premises. It was therefore decided, in the engineering phase, to foresee a tuning procedure before the final weldings to allow the same final result (precision on fundamental mode frequency) using fewer resources. This report explains the procedure for final check and tuning and gives an overview of the results achieved.