Tuning of the CERN 750 MHz RFQ for Medical Applications

CERN has built a compact 750 MHz RFQ as an injector for a hadron therapy linac. This RFQ was designed to accelerate protons to an energy of 5 MeV within only 2 m length. It is divided into four segments and equipped with 32 tuners in total. The RFQ length corresponds to 5λ which is considered to be close to the limit for simple field adjustment using tuners. Nevertheless the high frequency results in a sensitive structure and requires careful tuning by means of the alignment of the pumping ports and fixed tuners. This paper gives an overview of the tuning procedure and bead pull measurements of the RFQ.