F. Rondeaux

Status of the construction of the CMS magnet

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 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. The stored magnetic energy is 2.6 GJ. The magnet is being assembled in a surface hall and will be tested at the beginning of 2005 before being transferred 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 of CEA Saclay, ETH Zurich, Fermilab, INFN Genova, ITEP Moscow, University of Wisconsin and CERN. The return yoke, 21 m long and 14 m in diameter, is equivalent to a thickness of 1.5 m of saturated iron interleaved with four muon stations. Manufacture of the yoke and vacuum tank is completed and the first sub-detectors have been installed. The indirectly-cooled, pure-aluminum-stabilized coil is made up from five modules internally wound with four layers of a 20 kA mechanically-reinforced conductor. The manufacture of the conductor is completed and winding is in progress for a final assembly in 2004. All ancillaries are delivered or under contract. The magnet project is described, with emphasis on the present status of the fabrication.

Thermal conductivity measurements of epoxy systems at low temperature

We have developed a specific thermal conductivity measurement facility for solid materials at low temperature (LHe and LN2). At present, the Measurement of Thermal Conductivity of Insulators (MECTI) facility performs measurements on epoxy resin, as well as on bulk materials such as aluminum alloy and on insulators developed at Saclay. Thermal conductivity measurements on pre-impregnated fiber-glass epoxy composite are presented in the temperature range of 4.2 K to 14 K for different thicknesses in order to extract the thermal boundary resistance. We also present results obtained on four different bonding glues (Stycast 2850 FT, Poxycomet F, DP190, Eccobond 285) in the temperature range of 4.2 K to 10 K.

Design of the EuCARD High Field Model Dipole Magnet FRESCA2

This paper reports on the design of FRESCA2, a dipole magnet model wound with Nb3Sn Rutherford cable. This magnet is one of the deliverables of the High Field Magnets work package of the European FP7-EuCARD project. The nominal magnetic flux density of 13 Tesla in a 100 mm bore will make it suitable for upgrading the FRESCA cable test facility at CERN. The magnetic layout is based on a block coil, with four layers per pole. The mechanical structure is designed to provide adequate pre-stress, through the use of bladders, keys and an aluminum alloy shrinking cylinder.

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.

Studies of Lead Tungstate Crystal Matrices in High-Energy Beams for the CMS Electromagnetic Calorimeter at the LHC

Using matrices of lead tungstate crystals, energy resolutions better than 0.6% at 100 GeV have been achieved in the test beam in 1995. It has been demonstrated that a lead tungstate electromagnetic calorimeter read out by avalanche photodiodes can consistently achieve the excellent energy resolutions necessary to justify its construction in the CMS detector. The performance achieved has been understood in terms of the properties of the crystals and photodetectors.

Development of the EuCARD Nb3Sn Dipole Magnet FRESCA2

The key objective of the superconducting high field magnet work package of the European Project EuCARD, and specifically of the high field model task, is to design and fabricate the Nb3Sn dipole magnet FRESCA2. With an aperture of 100 mm and a target bore field of 13 T, the magnet is aimed at upgrading the FRESCA cable test facility at CERN. The design features four 1.5-m-long double-layer coils wound with a 21-mm-wide cable. The windings are contained in a support structure based on a 65-mm-thick aluminum shell pretensioned with bladders. In order to qualify the assembly and loading procedure and to validate the finite element stress computations, the structure will be assembled around aluminum blocks, which replace the superconducting coils, and instrumented with strain gauges. In this paper, we report on the status of the assembly and we update on the progress on design and fabrication of tooling and coils.

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.

Development of an Innovative Insulation for Nb3Sn Wind and React Coils

At the present time, Nb3Sn is the best superconductor candidate for the realization of high field magnets (>10–11 teslas). However its implementation remains delicate because of the great brittleness of material after the heat treatment necessary to form the Nb3Sn compounds. The conventional insulation for Nb3Sn wind & react coils requires performing, after the heat treatment, a vacuum resin impregnation, which adds to the cost and raises failure risk. We propose a one‐step innovating ceramic insulation deposited directly on the un‐reacted conducting cable. The conducting cable is wound according to conventional techniques and, after the heat treatment necessary to the form the Nb3Sn, we obtain a coil having a mechanical cohesion, while maintaining a proper conductor positioning and a suitable electric insulation. We will have studied the electric properties of superconducting cable isolated at the room temperature and at 4.2 K.

Shear test of glass reinforced composite materials at 4.2 K

Finite element analysis of the 4-T, 12.5-m long, 6-m-bore diameter superconducting solenoid for the CMS experiment at LHC shows that the insulation system is subjected mainly to shear forces during magnet operation at 4.5 K. This paper describes the development of a test procedure to evaluate shear properties of the glass reinforced composite material at 4.2 K. The calculation supporting the new specimen shape and the relation between coil and specimen Finite Element Analysis (FEA) are presented. As an application, this-test procedure is used to compare three different surface treatments of the conductor: solvent cleaning, sand blasting and anodic oxidation. Results from these tests are reported. Values up to 110 MPa at 4.2 K have been obtained for the CMS foreseen insulation material, the conductor being treated by anodic oxidation.

Assembly, Loading, and Cool-Down of the FRESCA2 Support Structure

This paper reports on the assembly process and cool-down to cryogenic temperature of the support structure of FRESCA2, which is a dipole magnet for upgrading the actual CERN cable test facility FRESCA. The structure of the FRESCA2 magnet is designed to provide the adequate pre-stress, through the use of keys, bladders, and an Al alloy shrinking cylinder. To qualify the assembly and loading procedures, the structure was assembled with Al blocks (dummy coils) that replaced the brittle Nb3Sn coils, and then cooled-down to 77 K with liquid nitrogen. The evolution of the mechanical behavior was monitored via strain gauges located on different components of the structure (shell, rods, yokes and dummy coils). We focus on the expected stresses within the structure after assembly, loading and cool-down. The expected stresses were determined from the 3-D finite element model of the structure. A comparison of the 3-D model stress predictions with the strain gauge data measurements is made. The coherence between the predicted stresses with the experimental gauge measurements will validate the FEM model of the structure.