Commissioning of the Linac4 Low Level RF and Future Plans

Linac4 is a new 86-m long normal-conducting linear accelerator that will provide 160 MeV H^{−} to the CERN PS Booster (PSB), and replace the present 50 MeV proton Linac2. The Low Level RF (LLRF) system has to control the RFQ, two choppers, three bunching cavities, twenty two accelerating cavities and one debuncher in the transfer line to the PSB. To optimize the transfer into the 1 MHz PSB bucket, the machine includes fast choppers (synchronized with the PSB RF) and a voltage modulation of the last two cavities that will provide Longitudinal Painting for optimum filling. The commissioning in the tunnel with beam has started in October 2013. So far the part consisting of the RFQ, the three bunching cavities, and the first DTL is operational. The rest of the machine will be progressively commissioned till end 2015. The paper presents the LLRF system. First results from the commissioning (with a prototype regulation system) are shown and the more sophisticated algorithms under development are presented

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