Monitoring Super Proton Synchrotron tunnel at CERN. Researchers using smart sensor technology to monitor geotechnical effects in the accelerator tunnels at CERN, the European particle physics laboratory, Switzerland. They are working in the Super Proton Synchrotron (SPS) accelerator, the first of the large accelerators at CERN. The SPS is an underground ring with a 7-kilometre circumference that extends across the border into France. It was completed in 1976. Magnets are used to control beams of particles as they are accelerated to high energies and smashed into targets or collided together. The SPS was used to discover the W and Z particles in 1983. It is now used to inject particles into even larger accelerators. Photographed on 23 January 2018.