A new pumping approach for the large electron positron collider (LEP)

Abstract

Storing particles inside an electron-positron collider brings about the need for low pressures to reduce interactions with residual gas molecules. In order to provide electron beams with a lifetime of 20 h, an average pressure of about 3×10 −9 Torr is needed for the Larger Electron Positron Collider (LEP), the construction of which has started in the proximity of CERN. Maintaining such a low pressure in spite of the small chamber cross-section and of the large degassing induced by synchrotron light requires an evenly distributed pumping speed. Traditionally, the problem is solved by means of integrated sputter ion pumps which are inserted all along the vacuum chamber and which make use of the field of the bending magnets. More recently a different linear pump, based on the use of a non-evaporable getter (NEG), was proposed. Laboratory measurements as well as real testing in an existing e +e − collider (PETRA at DESY), showed the feasibility and the advantages of this solution. The results which lead to the choice of NEG as main pump for LEP are presented and discussed.