S. Sgobba

The CMS conductor

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 13 m and the aperture is 6 m. This high magnetic field is achieved by means of a 4 layer, 5 modules superconducting coil. The coil is wound from an Al-stabilized Rutherford type conductor. The nominal current of the magnet is 20 kA at 4.5 K. In the CMS coil the structural function is ensured, unlike in other existing Al-stabilized thin solenoids, both by the Al-alloy reinforced conductor and the external former. In this paper the retained manufacturing process of the 50-km long reinforced conductor is described. In general the Rutherford type cable is surrounded by high purity aluminium in a continuous co-extrusion process to produce the Insert. Thereafter the reinforcement is joined by Electron Beam Welding to the pure Al of the insert, before being machined to the final dimensions. During the manufacture the bond quality between the Rutherford cable and the high purity aluminium as well as the quality of the EB welding are continuously controlled by a novel ultrasonic phased array system. The dimensions of the insert and the final conductor are measured by laser micrometer.

Progress of the ITER Correction Coils in China

The ITER Correction Coils (CC) include three sets of six coils each, distributed symmetrically around the tokamak to correct error fields. Each pair of coils, located on opposite sides of the tokamak, is series connected with polarity to produce asymmetric fields. The manufacturing of these superconducting coils is undergoing qualification of the main fabrication processes: winding into multiple pancakes, welding helium inlet/outlet on the conductor jacket, turn and ground insulation, vacuum pressure impregnation, inserting into an austenitic stainless steel case, enclosure welding, and assembling the terminal service box. It has been proceeding by an intense phase of R&D, trials tests, and final adjustment of the tooling. This paper mainly describes the progress in ASIPP for the CC manufacturing process before and on qualification phase and the status of corresponding equipment which are ordered or designed for each process. Some test results for the key component and procedure are also presented.

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.

Progress in Production and Qualification of Stainless Steel Jacket Material for the Conductor of the ITER Central Solenoid

When energized, the ITER Central Solenoid coils experience large pulsed electromagnetic forces that the conductor jacket itself must withstand. The conductor jacket consists of circle-in-square extruded and drawn austenitic stainless steel pipes. The qualification of the production of stainless steel jacket material was carried out on jackets manufactured in both a very low carbon AISI 316LN grade and a high Mn-bearing austenitic stainless steel, called JK2LB. Two different suppliers provided fully representative batch productions of both grades. Extensive metallurgical and dimensional metrology examinations were carried out at different steps of the processing, starting from the forged billets used as semifinished products to be engaged in the extrusion process, to the solution annealed jackets in their final shape. A specific method of Phased Array Ultrasonic Testing (PAUT) was developed and successfully applied for the non-destructive examination of the different jacket productions. PAUT sectorial scan inspections were carried out with probes traveling on the outer surface of the section, allowing almost 95% of the volume to be examined despite the complex geometry of the jacket.

Electrical and Mechanical Performance of an Enhanced Cable Insulation Scheme for Superconducting Magnets

New polyimide cable insulation schemes improving the cooling of Nb-Ti superconducting coils were recently developed to face the severe heat loads at which the next generation of superconducting accelerator magnets will work. In order to qualify the new insulation, a test campaign was realized to assess both its electrical and mechanical features with respect to the standard LHC insulation. The electrical tests assessed the dielectric strength and inter-turn leakage current to be satisfactory. The mechanical tests investigated the insulation thickness under load and the stress relaxation at ambient temperature, thus providing essential information for the magnetic and mechanical design of the final focusing magnets for the LHC upgrade phase I.

Toward an Improved High Strength, High RRR CMS Conductor

CMS (Compact Muon Solenoid) is a general-purpose detector designed to run at the CERN Large Hadron Collider (LHC), including a 4-layer superconducting solenoid with 6 m diameter by 12.5 m long free bore operated at 4 T and at 4.5 K. The Rutherford type superconductor, stabilized by high purity 99.998% aluminum, is reinforced by aluminum alloy sections welded to the superconductor by electron beam. Due to the high magnetic forces at nominal field inside the winding pack, the conductor itself represents a main structural component to get a self-supporting winding structure. In view of an upgrade oriented to a possible new project, an improvement of the mechanical performances of the reinforced conductor starting from the CMS concept has been considered, aimed to increase the reachable field based on an optimized layout

Mechanical properties of the CMS conductor

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 10000 ton return yoke. The magnetic field is achieved by a 4-layer superconducting solenoid made of a high purity aluminum (HPA) stabilized Rutherford type superconductor. The magnet is operated at 4.5 K, with a nominal current of 20 kA, for a total stored magnetic energy of 2.7 GJ. Due to the high magnetic forces at nominal field inside the winding pack, the structural component is the conductor itself to get a self-supporting winding structure. The mechanical reinforcement is made from aluminum alloy directly welded to the superconductor by electron beam (EB) welding technology before the winding operation. The external support cylinders also take part to the mechanical integrity. At each step of fabrication of the CMS conductor, the mechanical properties of the components and bonding between them are measured by destructive testing on short samples, in complement of continuous monitoring during production. This paper presents the results of the superconducting cable to pure aluminum shear testing, the tensile testing of the EN AW 6082 aluminum reinforcement, the insert to reinforcement shear testing, and the tensile testing of the full conductor before and after heat treatment induced during coil curing. Possible influence of the EB welding on the mechanical properties of the final conductor is investigated. Residual resistivity ratio (RRR) measurements of the HPA stabilizer are presented. Mechanical properties and equivalent RRR of the CMS conductor are presented for comparison with conductors of other geometry.

Continuous EB welding of the reinforcement of the CMS 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. In order to withstand the electro-mechanical forces during the operation of the CMS magnet, the superconducting cable embedded in a 99.998% pure aluminum matrix is reinforced with two sections of aluminum alloy EN AW-6082 assembled by continuous Electron Beam Welding (EBW). A dedicated production line has been designed by Techmeta, a leading company in the field of EBW. The production line has a total length of 70 m. Non-stop welding of each of the 20 lengths of 2.5 km, required to build the coil, will last 22 hours. EBW is the most critical process involved in the production line. The main advantage of the EBW process is to minimize the Heat Affected Zone; this is particularly important for avoiding damage to the superconducting cable located only 4.7 mm from the welded joints. Two welding guns of 20 kW each operate in parallel in a vacuum chamber fitted with dynamic airlocks. After welding, the conductor is continuously machined on the four faces and on each corner to obtain the required dimensions and surface finish. Special emphasis has been put on quality monitoring. All significant production parameters are recorded during operation and relevant samples are taken from each produced length for destructive testing purposes. In addition, a continuous phased array ultrasonic checking device is located immediately after the welding unit for the continuous welding quality control, along with a dimension laser measurement unit following the machining.

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.

Mechanical performance at cryogenic temperature of the modules of the external cylinder of CMS and quality controls applied during their fabrication

The CMS experiment (Compact Muon Solenoid) is a general-purpose proton-proton detector designed to run at the highest luminosity at the Large Hadron Collider (LHC). Distinctive features of the CMS detector include a high-magnetic-field solenoid (4 T) coupled with a multilayer muon system, a fully active scintillating-crystal electromagnetic calorimeter, a tile hadronic calorimeter, and a powerful inner tracking system. The superconducting solenoid (6 m diameter by 12.5 m long free bore) is enclosed inside a 10,000 t return yoke. The external cylinder of the CMS coil consists of five modules having an inner diameter of 6.8 m, a thickness of 50 mm and an individual length of 2.5 m. The cylinder shall feature a yield strength of 209 MPa at its working temperature of 4.5 K. The structural material selected for the components of the cylinders is the non heat-treatable aluminum alloy EN AW-5083. Each module of the cylinder is composed of a 50 mm thick shell, manufactured by bending and welding thick plates of strain hardened EN AW-5083-H321, of two 130 mm thick end flanges fabricated as seamless rolled rings and circumferentially welded to the shells, and of radial shoulders of the same alloy, to which the coil support system is attached through tie-rods. The components (seamless rings, plates, shoulders) and the manufacturing methods have been fully validated by a systematic assessment down to cryogenic temperature of the mechanical properties on samples issued from full scale parts, and by a rigorous qualification of the fabrication welds, performed on weld extra-lengths issued from each one of the modules.