Design Study of a Large Electron-Positron Colliding Beam Machine - LEP

Early in 1976 a study group at CERN began to examine design concepts for a Large Electron-Positron storage ring, LEP. At that time, 50 km circumference and 100 GeV per beam - to be obtained with a conventional radio frequency system - were chosen. This first study was terminated with several problems still unsolved, including extreme sensitivity of orbit stability to closed-orbit tolerances, operation in collision mode with electrostatically separated beams and technical difficulties due to the low magnetic field at injection. In addition, the estimated cost was considered high. A fresh start was made in the second half of 1977. In order to explore the variation of difficulties and cost with machine size and in an attempt to arrive at a solid base for an entirely feasible machine, it was decided to reduce the nominal energy to 70 GeV while retaining the target for maximum luminosity at 1032cm-2s-1. The optimum radius for this design - later confirmed by the outcome of the study - is 3.5 km. This phase of the study ended in August 1978 with the issuing of a detailed Design Report including a cost estimate. The conclusions are that such a machine is not only feasible but that it can be developed to reach 100 GeV per beam when suitable superconducting cavities become available. In fact, the design is made such that this extension of energy requires no major change other than the substitution of cavities.