Operation of the Four 12 KW at 4.5K Refrigerators for LEP
In 1998 the first energy upgrade of the LEP Electron/Positron collider, LEP2, was completed at CERN. Sixty-eight superconducting modules supplied by four 12 kW @ 4.5 K equivalent power refrigerators have been operated allowing a colliding beam energy of 94.5 GeV. Meanwhile, the operation and maintenance responsibilities were transferred to an industrial firm on the basis of a result-oriented contract. After a short description of the operational organization, we report on the operation of the LEP2 cryogenic system over the past three years. Particular attention is given to power availability, failure statistics and recovery time after interruptions. The most relevant problems and their solutions are exposed. Finally, we review the interactions between the cryogenic system and the particle beams, which are limiting the ultimate performance of the LEP collider.
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