The LHC Test String 2 is a 107-m long superconducting magnet string representing a full-cell of the LHC machine. It was designed and commissioned at CERN in order to validate the final design choices and to investigate the collective behavior and operation modes of the LHC machine systems. It has been commissioned and operated since April 2001 and has accumulated more than 8000 hours at its nominal operating temperature of 1.9 K under machine-like conditions. We report on the experimental validation of the supercritical and superfluid helium cooling loops, quench propagation and recovery, heat loads, as well as on investigation of operational performances, advanced control techniques, process control, instrumentation and long term behavior under electrical and thermal cycling. ABSTRACTThe LHC Test String 2 is a 107-m long superconducting magnet string representing a full-cell of the LHC machine. It was designed and commissioned at CERN in order to validate the final design choices and to investigate the collective behavior and operation modes of the LHC machine systems. It has been commissioned and operated since April 2001 and has accumulated more than 8000 hours at its nominal operating temperature of 1.9 K under machine-like conditions. We report on the experimental validation of the supercritical and superfluid helium cooling loops, quench propagation and recovery, heat loads, as well as on investigation of operational performances, advanced control techniques, process control, instrumentation and long term behavior under electrical and thermal cycling.

The largest cryogenic test facility at CERN, located at Zone 18, is used to validate and to test all main components working at cryogenic temperature in the LHC (Large Hadron Collider) before final installation in the machine tunnel. In total about 1300 main dipoles, 400 main quadrupoles, 5 RF-modules, eight 1.8 K refrigeration units will be tested in the coming years. The test facility has been improved and upgraded over the last few years and the first 18 kW refrigerator for the LHC machine has been added to boost the cryogenic capacity for the area via a 25,000 liter liquid helium dewar. The existing 6 kW refrigerator, used for the LHC Test String experiments, will also be employed to commission LHC cryogenic components. We report on the design and layout of the test facility as well as the commissioning and the first 10,000 hours operational experience of the test facility and the 18 kW LHC refrigerator. ABSTRACTThe largest cryogenic test facility at CERN, located at Zone 18, is used to validate and to test all main components working at cryogenic temperature in the LHC (Large Hadron Collider) before final installation in the machine tunnel. In total about 1300 main dipoles, 400 main quadrupoles, 5 RF-modules, eight 1.8 K refrigeration units will be tested in the coming years.The test facility has been improved and upgraded over the last few years and the first 18 kW refrigerator for the LHC machine has been added to boost the cryogenic capacity for the area via a 25,000 liter liquid helium dewar. The existing 6 kW refrigerator, used for the LHC Test String experiments, will also be employed to commission LHC cryogenic components.We report on the design and layout of the test facility as well as the commissioning and the first 10,000 hours operational experience of the test facility and the 18 kW LHC refrigerator.

The cryogenic infrastructure of the station for testing LHC prototype superconducting magnets in superfluid helium below 2 K has been upgraded. Liquid nitrogen precooling has permitted to increase the liquefaction capacity of the refrigerator. The addition of cold centrifugal compressors with a pressure ratio of 3:1 has boosted the capacity of the warm pumping unit. To ensure adaptation of the pumping capacity, a heater-and-valve box allows to bypass the cold compressors. This box also comprises a 32 kW electrical heater for warming up the low-pressure gaseous helium before it enters the volumetric warm pumping unit. Possible impurities in the helium returning from the subatmospheric circuits are trapped in a freeze-out helium cleaner. Automatic process control and supervision permit unattended operation and optimal management of the helium inventory.

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The Large Hadron Collider (LHC) cryogenic system comprises eight independent refrigeration and distribution systems that supply the eight 3.3 km long accelerator sectors with cryogenic refrigeration power as well as four refrigeration systems for the needs of the detectors ATLAS and CMS. In order to ensure the highest possible reliability of the installations, it is important to apply a reliability centred approach for the maintenance. Even though large scale cryogenic refrigeration exists since the mid 20th century, very little third party reliability data is available today. CERN has started to collect data with its computer aided maintenance management system (CAMMS) in 2009, when the accelerator has gone into normal operation. This paper presents the reliability observations from the operation and the maintenance side, as well as statistical data collected by the means of the CAMMS system.