Upgrade of Four Cryogenic Helium Refrigerators used in the LEP Collider for LHC Refrigeration

After the final run of the Large Electron Positron Collider, the four refrigerators used for LEP were free to be used for the Large Hadron Collider project. In order to serve the LHC requirements, these four Ex-LEP refrigerators needed to be modified and upgraded. In this paper we present the requirements for these refrigerators operating for the LHC machine compared to those for LEP, the necessary modifications of the existing machinery and the additional equipment needed. We will also compare the cost of the upgrades with the cost of the new LHC refrigerators.