Installation in the LNL ALPI linac of the first cryostat with four niobium quarter wave resonators

Quarter Wave Resonators (QWRs) can be fabricated by sputtering a niobium thin film onto an OFHC copper base. After a deep investigation of DC biased diode sputtering in cylindrical configuration, the coating procedure has become well-established for the cavities of the LNL ALPI-linac 0.14 beta section and it is under progressive improvement for lower beta cavities. A first cryogenic module with four sputtered QWRs was installed in ALPI. All resonators sputtered during laboratory tests provided Q-values of the order of 109 and accelerating fields around 7 MV/m at 7 W. Accelerating field values up to 4.2 MV/m are instead achieved by the four resonators installed along the beam line. This shows that severe attention should be paid to the installation procedure into a real accelerating machine and that further study is needed for a future serial production.