CEPC Conceptual Design Report: Volume 1 - Accelerator

The Circular Electron Positron Collider (CEPC) is a large international scientific project initiated and hosted by China. It is located in a 100-km circumference underground tunnel. The accelerator complex consists of a linear accelerator (Linac), a damping ring (DR), the Booster, the Collider and several transport lines. In the tunnel, space is reserved for a future pp collider, SPPC. The CEPC center-of-mass energy is 240 GeV, and at that collision energy will serve as a Higgs factory. The design also allows operation at 91 GeV for a Z factory and at 160 GeV for a W factory. The heart of the CEPC is a double-ring collider. It has two interaction points where are located large detectors. The Booster is in the same tunnel above the Collider. It is a synchrotron with a 10 GeV injection energy and extraction energy equal to the beam collision energy. The repetition cycle is 10 seconds. Top-up injection will be used to maintain constant luminosity. The 10 GeV Linac, injector to the Booster, built at ground level, accelerates both electrons and positrons. A 1.1 GeV damping ring reduces the positron emittance. Transport lines made of permanent magnets connect the Linac to the Booster. In addition to particle physics, the Collider can operate simultaneously as a powerful synchrotron radiation (SR) light source. It will extend the usable SR spectrum into an unprecedented energy and brightness range. Two gamma-ray beamlines are included in the design. Prior to the construction will be a five-year R&D period (2018-2022). Construction is expected to start in ~2022 and be completed in ~2030. This report is a summary of work accomplished during the past several years by hundreds of scientists and engineers at home and abroad. The current volume, Volume I, is on the accelerators. A separate volume, Volume II, will be on physics and the detectors.