Proton beam commissioning of the SPIRAL2 Single Bunch Selector

The single bunch selector of the SPIRAL2 accelerator allows reducing the bunch rate to the target of the Neutron For Science (NFS) facility in view of time of flight experiments. It involves two processes: a static dipole magnet deviates the beam on a 7.3 kW scraper, while the electric field of two high voltage travelling wave pulses maintains the selected bunch on axis at the required repetition rate. This original principle, named "inverted duty cycle", was chosen to provide reasonable power requirement for the pulse generators, high rejection of the side bunches, and safe operation for the experimental target. This paper gives an overview of the whole system, recalls the main component design issues and performances and reports the successful commissioning results with the first 0.2 and 5 mA proton beams.