operated in tandem with Antiproton Collector (AC), to form the Antiproton Accumulation Complex (AAC). The Antiproton Collector (AC), built 1986–1987, operations ended in 1997 and the machine was converted into the Antiproton Decelerator (AD), which is the successor machine for Low Energy Antiproton Ring (LEAR). Operated in tandem with Antiproton Accumulator (AA) and the pair formed the Antiproton Accumulation Complex (AAC), whose purpose was to store antiprotons produced by the Proton Synchrotron (PS) for use in other experiments and accelerators, like the Low Energy Antiproton Ring (LEAR) and Super Proton–Antiproton Synchrotron (SpS). The Compact Linear Collider Test Facility 3 (CTF3), which studied feasibility for the future normal conducting linear collider project (the CLIC collider). In operation 2001–2016. One of its beamlines has been converted, from 2017 on, into the new CERN Linear Electron Accelerator for Research (CLEAR) facility. Possible future accelerators CERN, in collaboration with groups worldwide, is investigating two main concepts for future accelerators: A linear electron-positron collider with a new acceleration concept to increase the energy (CLIC) and a larger version of the LHC, a project currently named Future Circular Collider. Sites The smaller accelerators are on the main Meyrin site (also known as the West Area), which was originally built in Switzerland alongside the French border, but has been extended to span the border since 1965. The French side is under Swiss jurisdiction and there is no obvious border within the site, apart from a line of marker stones. The SPS and LEP/LHC tunnels are almost entirely outside the main site, and are mostly buried under French farmland and invisible from the surface. However, they have surface sites at various points around them, either as the location of buildings associated with experiments or other facilities needed to operate the colliders such as cryogenic plants and access shafts. The experiments are located at the same underground level as the tunnels at these sites. Three of these experimental sites are in France, with ATLAS in Switzerland, although some of the ancillary cryogenic and access sites are in Switzerland. The largest of the experimental sites is the Prévessin site, also known as the North Area, which is the target station for non-collider experiments on the SPS accelerator. Other sites are the ones which were used for the UA1, UA2 and the LEP experiments (the latter are used by LHC experiments). Outside of the LEP and LHC experiments, most are officially