Commissioning and Operational Experience Gained with the Linac4 RFQ at CERN

The installation of Linac4 has started in 2013 with the 3 MeV Front End, aiming at delivering a fully commissioned 160 MeV H^{−} beam by 2016. During summer 2013 the H^{−} ion source, a clone of the first prototype, and the Low Energy Beam Transport lines have been installed in the Linac4 tunnel followed shortly by the Radiofrequency Quadrupole accelerator (RFQ), operating at the RF frequency of 352.2 MHz and which accelerates the ion beam to the energy of 3 MeV. The RFQ, which had already been commissioned at the 3 MeV Test Stand, was this time driven by a fully digital LLRF system. This paper reports the result of the bead-pull field check performed after the installation in the tunnel, the experience gained during recommissioning and the results of field characterization as a function of the water temperature in the RFQ cooling channels, showing how the accelerating field can be adjusted by simply tuning the different cavity modules.