Commissioning of ALPS, the New Beam Position Monitor System of CERN’s Super Proton Synchrotron

The Super Proton Synchrotron (SPS) is both, the final machine in the pre-accelerator chain of the Large Hadron Collider (LHC) at CERN, and a machine providing several experiments with proton and ion beams. In the framework of CERN’s LHC Injectors Upgrade (LIU) project, aimed at improving the performances of the pre-accelerators in view of the high-luminosity upgrade of the LHC, the Beam Position Monitor (BPM) system of the SPS was redesigned during Run 2 of the LHC and deployed during the subsequent Long Shutdown 2 (LS2). This new system is called ALPS (A Logarithmic Position System) and acquires the signals from some 240 BPMs. It is designed to improve the system’s reliability and reduce the required maintenance with respect to its predecessor. During the restart of the SPS in 2021, the BPM system was a key element of the fast recommissioning of the machine, proving the validity of the chosen design approach and pre-beam commissioning strategy. This paper aims to illustrate the design choices made for ALPS, the strategy for commissioning it with beam in parallel with the machine restart, the commissioning procedure and the results obtained.