Commissioning of the CMS Cryogenic System After Final Installation in the Underground Cavern

After having served for the surface tests of the Compact Muon Solenoid (CMS) magnet, the cold box and ancillaries of the CMS helium refrigerator have been dismantled, moved and re-installed in the USC55 cavern in 2007. The full re-commissioning in the cavern has been followed by several tests of the refrigerator to confirm its nominal performance before it was used for the magnet and detector tests in 2008. During these tests the safety modes of the refrigeration system have been tested and improved. After a nine-year project both, the magnet and the refrigeration system are now ready for the CMS operation

The helium cryogenic plant for the CMS superconducting magnet

A new helium refrigeration plant with a cooling capacity of 800 W at 4.45 K, 4500 W between 60 K and 80 K, and 4 g/s liquefaction simultaneously has been designed and is presently being constructed by Air Liquide for CERN. The refrigeration plant will provide the cooling power for the cool down and the operation of the CMS (Compact Muon Solenoid) superconducting coil whose cold mass weighs 225 t. The refrigeration plant will at first be installed in a surface building for the tests of the superconducting magnet. On completion of the tests the cold box will be moved to its final underground position next to the CMS experimental cavern. This paper presents the process design, describes the main components and explains their selection. (4 refs)

Cryogenics for the Large Hadron Collider Experiments

High Energy Physics experiments have frequently adopted cryogenic versions of their apparatus to achieve the desired performance. Among the four new experiments for the CERN Large Hadron Collider (LHC) the two largest, ATLAS and CMS, include spectrometers using 4.5 K superconducting magnets and detectors filled with liquid argon at 87 K, respectively for particle momentum and energy measurements. These detectors are of unprecedented size and complexity and the definition of the associated cryogenic systems is the result of a collaboration between CERN and several external institutes all around the world. A review of the various systems is presented with particular emphasis to the basic cooling principles, the special cryogenic features and the operation scenarios

Commissioning of the CMS Magnet

CMS (Compact Muon Solenoid) is one of the large experiments for the LHC at CERN. The superconducting magnet for CMS has been designed to reach a 4 T field in a free bore of 6 m diameter and 12.5 m length with a stored energy of 2.6 GJ at full current. The flux is returned through a 10 000 t yoke comprising of five wheels and two end caps composed of three disks each. The magnet was designed to be assembled and tested in a surface hall, prior to be lowered at 90 m below ground, to its final position in the experimental cavern. The distinctive feature of the cold mass is the four-layer winding, made from a reinforced and stabilized NbTi conductor. The design and construction was carried out by CMS participating institutes through technical and contractual endeavors. Among them CEA Saclay, INFN Genova, ETH Zurich, Fermilab, ITEP Moscow, University of Wisconsin and CERN. The construction of the CMS Magnet, and of the coil in particular, has been completed last year. The magnet has just been powered to full field achieving electrical commissioning. After a brief reminder of the design and construction the first results of the commissioning are reported in this paper

Status of the CMS magnet (MT17)

The CMS experiment (Compact Muon Solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with a free bore of 6 m diameter and 12.5-m length, enclosed inside a 10 000-ton return yoke. The magnet will be assembled and tested in a surface hall at Point 5 of the LHC at the beginning of 2004 before being transferred by heavy lifting means to an experimental hall 90 m below ground level. The design and construction of the magnet is a common project of the CMS Collaboration. The task is organized by a CERN based group with strong technical and contractual participation from CEA Saclay, ETH Zurich, Fermilab, INFN Genova, ITEP Moscow, University of Wisconsin and CERN. The magnet project will be described, with emphasis on the present status of the fabrication. (15 refs)

Performance of the CMS Cathode Strip Chambers with Cosmic Rays

The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47 microns to 243 microns. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns

Performance and Operation of the CMS Electromagnetic Calorimeter

The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented