Visiting Building 887, the largest of CERN's experiment halls, is always an astonishing experience. Hundreds of concrete blocks stretch as far as the eye can see, surrounded by enormous gantry cranes. Between the blocks, you'll glimpse a detector component awaiting testing here, a long-term experiment there and, over there, an inconspicuous beamline carrying its particles to their destination a bit further on. Welcome to the Kingdom of the North, where reigns the Super Proton Synchrotron (SPS). The accelerator sends particles to some 60 user areas and experiments via six beamlines of a total length of 6 kilometres.
Building 887 (also called EHN1, for North Experimental Hall 1) is 55 metres wide and 330 metres long (!) and is therefore CERN's biggest. But the North Area is vaster still: it also includes the Neutrino Platform, housed in a recent extension of Building 887, several other halls that are home to the "NA" (North Area) experiments, such as NA58 (COMPASS), NA61 (SHINE), NA62 and NA64, as well as many test areas, essential for the development of future detector and accelerator components.
Most of the equipment in the North Area dates from when the SPS started up in 1976. Several upgrades have therefore been scheduled for Long Shutdown 2, although the ambitious consolidation programme initially planned will need to be completed over a longer period. "The initial consolidation work taking place during LS2 focuses mainly on the safety of the installations," says Johannes Bernhard of the Engineering department, who is responsible for liaising with the experiments (EN-EA group). The gas supply system is being renovated, which involves replacing several hundreds of metres of pipes. The radiation detection system is also being renovated and the layout of Hall 887 will be modified in order to extend the testing area for new detectors. The LHC experiments, in particular, need facilities to test the new subdetectors that they will use in the high-luminosity LHC era.
Hall 888 (EHN2) sits right at the end of the Prévessin site and houses the COMPASS experiment. Two brand new gantry cranes have been installed there and, as is the case across the whole of the North Area, the gas supply system has been renovated. Several components of the COMPASS experiment, which studies the structure of nucleons, are being upgraded. After LS2, the detector will receive muons at an energy of 160 GeV (instead of hadrons at 190 GeV, as was the case during the previous run). New subdetectors, scintillators and silicon microstrip detectors will be installed, as well as a new acquisition system.
Work is also under way on the NA62 experiment, housed in Building 918 (EHN3), which studies the decay of rare kaons. At the entrance to the building, visitors and users are greeted by a brand new access systems. The experiment's beamline will be modified in order to measure kaon decays with even greater precision and efficiency and to reduce the background. Finally, a new experiment area is being prepared for NA64, which is investigating dark matter. "The collaboration with all equipment and service groups has been key to defining and executing the workplan for LS2, and we look forward to the restart of operations in a much improved situation," says Johannes Bernhard on behalf of the EN-EA group.
Beyond LS2, the North Area is looking to the future with the Physics Beyond Colliders programme: several experiment projects, such as the BDF, propose to use the SPS lines. Implementation studies are being finalised to install a test area on the muon beamline of the EHN2 building. Several experiment projects, such as NA64mu, MuonE and AMBER, the successor to COMPASS, could be tested there.
