P. Fabbricatore

Status of the CMS magnet

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.

Final design of the CMS solenoid cold mass

The 4 T, 12.5 m long, 6 m bore diameter superconducting solenoid for the CMS (Compact Muon Solenoid) experiment at LHC will be the largest and the most powerful superconducting solenoid ever built. Part of the CMS design is based on that of previous large superconducting solenoids-the use of a high purity aluminium stabilized conductor, a compact impregnated winding with indirect cooling and quench back protection process. However, the dimensions and the performances of this solenoid have imposed solutions which are more than extrapolations of the previous ones : the use of a mechanically reinforced conductor and a five module winding, each module being made of four layers, internally wound. This design, which is now frozen, relies on numerous magnetic, mechanical and thermal calculations, on various experimental tests (characterization of structural and insulating materials, electrical joints...) and specific mock-ups. Two pre-industrialization programs, concerning the conductor and the winding process have also been carried out with industrial partners to support the foreseen solutions. Both the final design and the experimental results obtained to validate this design are presented in this paper.

The mechanical and thermal design for the MICE detector solenoid magnet system

The detector solenoid for MICE surrounds a scintillating fiber tracker that is used to analyze the muon beam within the detector. There are two detector magnets for measuring the beam emittance entering and leaving the cooling channel that forms the central part of the experiment. The field in the region of the fiber detectors must be from 2.8 to 4 T and uniform to better than 1 percent over a volume that is 300 mm in diameter by 1000 mm long. The portion of the detector magnet that is around the uniform field section of the magnet consists of two short end coils and a long center coil. In addition, in the direction of the MICE cooling channel, there are two additional coils that are used to match the muon beam in the cooling channel to the beam required for the detectors. Each detector magnet module, with its five coils, will have a design stored-energy of about 4 MJ. Each detector magnet is designed to be cooled using three 1.5 W coolers. This report presents the mechanical and electrical parameters for the detector magnet system.

The construction of the modules composing the CMS superconducting coil

CMS (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 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. The construction of the five modules composing the coil is presently under way. The methods for constructing large aluminum alloy mandrels, for winding the reinforced conductor with high accuracy of the winding pack and for impregnating the single large modules (50 t) have been assessed through the construction of a module prototype. The prototype has the same radius as a CMS module (6900 mm outer diameter), but a shorter axial length (670 mm against 2500 for the module). The relevant technological result was the understanding of the methods for obtaining a large coil with a very limited shape deformation (/spl plusmn/2.5 mm on diameter) for allowing the precise mounting of the modules. This paper describes the main technical issues of the prototype and of the construction of the first modules, the geometrical and RT tests performed on them and the common problems related to the series construction of large superconducting coils.

A superconducting magnet for a beam delivery system for carbon ion cancer therapy

The therapy of cancer (hadrontherapy) with accelerated particle beams is an out coming method that allows an accurate and effective treatment of several kinds of tumors minimizing the irradiation of the surrounding tissues and avoiding intercepting vital organs. The deep tumors are usually treated with proton or ion beams by using a rotating gantry that allows the 360/spl deg/ irradiation around the patient. For carbon ion hadrontherapy being the energy in the order of 400 MeV, huge gantries structure are required if resistive magnets are used. The size of a ion gantry can be of the order of 10 m in diameter and 100 tons in weight. An alternative solution has been studied, involving the use of a cryogenic free superconducting magnet. The magnet consists of ten 90/spl deg/ bent superconducting dipoles wound with an aluminum stabilized Cu/NbTi conductor and mechanically supported by an aluminum alloy structure. An optimization of the magnetic design is running by using genetic algorithms with the goal to obtain a field homogeneity within 0.2% in a region of 60/spl times/200 mm/sup 2/ along the beam path. Furthermore, an accurate study of the winding technique is in progress. The magnet will be kept at 4.5 K by a cooling system based on two cryocoolers operating alternately in steady state or together during the cool down and the electrical transients. The current is supplied via a couple of HTCS current leads always connected. In the paper, a description of the design is given.

Critical current measurements on the CMS stabilized conductor

The Compact Muon Solenoid (CMS) is one of the general-purpose detectors to be provided for the LHC project at CERN. The design field of the CMS superconducting magnet is 4 T, the magnetic length is 12.5 m and the free bore is 6 m. Critical current measurements in fields up to 6 T have been performed on the CMS stabilized conductors using the MA.RI.S.A. test facility at INFN-Genova. A comparison among the measurements gives information about the possible critical current degradation and assures an accurate quality control of the conductor production.

Status report on the CMS superconducting solenoid for LHC

The CMS (Compact Muon Solenoid) experiment is one of the two large experiments approved to be installed on the Large Hadron Collider (LHC) at CERN, and is now at an early stage of construction. For good momentum resolution, a superconducting solenoid is needed, the main characteristic of which is a nominal magnetic field of 4 T in a 5.9 m diameter and 12.5 m long warm bore, leading to a stored energy of 2.7 GJ. These characteristics make this superconducting solenoid the largest and most powerful one ever designed. The main technical choices are: the use of a mechanically reinforced Al-stabilized conductor, the subdivision of the coil in five modules, each internally wound and vacuum impregnated before final assembly, the use of indirect cooling with circulation of liquid helium in a thermosyphon mode and quench back protection process to enhance the energy dump. All these choices need developments which will be reported together with the detailed description and the status of each main component of the cold mass of the solenoid.

Finite element stress analysis of the CMS magnet coil

The Compact Muon Solenoid (CMS) is one of the experiments which are being designed in the framework of the Large Hadron Collider (LHC) project at CERN. The design field of the CMS magnet is 4 T, the magnetic length is 12.38 m and the aperture is 6.36 m. This is achieved with a 4 layer-5 module superconducting Al-stabilized coil energised at a nominal current of 20 kA. The finite element analysis (FEA) carried out is axisymmetric elasto-plastic. FEA has also been carried out on the suspension system and on the conductor.

Experimental study of CMS conductor stability

Several computations have been carried out in last years to evaluate stability against disturbances of the CMS coil. The results coming from finite element analysis have shown that the Minimum Quench Energy is between 0.43 and 0.855 depending on the model describing the transition from superconducting to normal state. The corresponding Minimum Propagating Zone is quite short, ranging between 10 and 20 cm. This very short MPZ allows to perform experimental measurements on short samples. This has been done using circular samples (400 mm in diameter) energized to 20 kA by the transformer method. The applied field ranging between 3.5 and 6 T, is provided by the Ma.Ri.S.A. Facility at INFN Geneva. A comparison between computations and experimental results is presented.

The winding line for the CMS reinforced conductor

The Compact Muon Solenoid (CMS) is one of the general-purpose detectors to be provided for the LHC project at CERN. The design field of the CMS superconducting magnet is 4 T, the length is 12.5 m and the free bore is 6 m. The use of a reinforced conductor for the CMS coil required a sustained activity of development at industrial level, to understand how to handle, to pre-bend and to wind the conductor with an inner winding technique. The winding line was designed and constructed according to this experience. The working principles of the line are under test through the winding of a prototype of a CMS coil module. The prototype has the same radius of a CMS module (6900 mm outer diameter), but a shorter axial length (670 mm against 2500 for the module). The critical operations are related to the accurate pre-bending of the conductor, the positioning of the turns into the winding, the axial compaction, and the correct handling of 50-ton windings.