Commissioning of the CMS Magnet

Abstract

Abstract-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.

Design and Description of the CMS Magnetic System Model

“…In the Compact Muon Solenoid (CMS) detector [11] at the LHC [8], the magnetic field is provided by a wide-aperture superconducting thin solenoid [33] with a diameter of 6 m and a length of 12.5 m, where a central magnetic flux density |B 0 | of 3.8 T is created by an operational direct current of 18.164 kA [34][35][36]. The CMS multi-purpose detector, schematically shown in Figure 1, includes a silicon pixel tracking detector [37], a silicon strip tracking detector [38], a solid crystal electromagnetic calorimeter [39] to register e and γ particles, and a hadron calorimeter of total absorption [40] both located inside the superconducting solenoid, as well as a muon spectrometer [41][42][43][44] and a forward hadron calorimeter [45], both located outside of the superconducting coil.…”

Cryogenics Activities at the Institute of Research into the Fundamental Laws of the Universe (Irfu)

“…On the basis of a collaboration with CERN since 1996, Irfu (previously named Dapnia) was involved in the overall design, production and testing of the superconducting solenoid for the CMS (Compact muons solenoid) experiment installed at CERN on the LHC (Large Hadron Collider) 1) .The LCSE was in charge of the thermal design of the proximity cryogenics and the tests of its different components such as the phase separator/reservoir, the currents leads 2) , the titanium support rods and a large thermosiphon loop reproducing the cryogenic loop of the CMS magnet 3) . The concept of cooling such a magnet with a two-phase thermosiphon at 4.5 K was proposed by LCSE and accepted by CERN.…”

Experience Gained From the Construction, Test and Operation of the Large 4-T CMS Coil

“…The magnet has been assembled [2], tested [3], [4] and mapped [5] in a surface hall during the autumn 2006, and it is being lowered in the underground area by heavy lifting means. This bold choice has decoupled the work on the magnet assembly and test from the construction of the experimental area.…”