Baynham, D E

Buskop, J

Carr, F S

Dudarev, A

Holtom, E

ten Kate, H H J

Towndrow, E F

CERN Document Server

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 16, NO. 2, JUNE 2006 537ATLAS End Cap Toroid Cold Massand Cryostat IntegrationD. E. Baynham, F. S. Carr, E. Holtom, E. F. Towndrow, H. H. J. ten Kate, A. Dudarev, and J. BuskopAbstract—The ATLAS experiment at LHC (CERN) will utilize alarge, superconducting, air-cored toroid magnet system with a longBarrel Toroid and two End Cap Toroids. Each End Cap Toroid willcontain eight racetrack coils mounted as a single cold mass in acryostat vessel of approximately 10 m diameter.This paper presents the design principles and realization of thecold mass assembly. The procedures for integration of the full coldmass, 120 tonnes, into the vacuum cryostat are described. Theoverall status of toroid magnet integration and planning for testand installation is reviewed.Index Terms—Assembly, magnet, superconducting, toroid.I. INTRODUCTIONTHE ATLAS muon spectrometer is based on a supercon-ducting toroid magnet system [1] consisting of a longBarrel Toroid (BT) and two End Cap Toroids (ECT’s). Themajor features of the End Cap Toroid Magnets have beendescribed elsewhere [2], [3]. Each ECT consists of a cold mass,eight superconducting coil modules and eight keystone boxes,mounted in a large castellated cryostat [3]. The cold mass willbe directly cooled by pumped circulation of two phase helium.All services will be carried through a single turret.In this paper we describe the final industrial fabrication ofmajor components, their delivery to CERN and the integrationto form the final Cold Mass and Toroid assembly.II. COLD MASS FABRICATION IN INDUSTRYThe Cold Mass consists of eight superconducting coils andeight keystone box modules. The keystone box modules are thestructural elements that maintain the toroidal shape under grav-itational and magnetic loads. The cold mass components weremanufactured by BRUSH HMA BV in the Netherlands under acontract placed by NIKHEF, Amsterdam. The total fabricationrequired 16 coils and 16 keystone box (KSB) modules for theassembly of two complete toroids. Coil and keystone box fabri-cation has been described previously [2]. Industrial winding andimpregnation of the coil modules was completed in April 2004.In parallel with the coil manufacture a test assembly of a fullcold mass was made at the manufacturers works, see Fig. 1. Theassembly was made with toroid axis vertical and confirmed theManuscript received September 20, 2005.D. E. Baynham, F. S. Carr, E. Holtom, and E. F. Towndrow are with theCCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxonshire OX110QX, U.K. (e-mail: d.e.baynham@ rl.ac.uk).H. H. J. ten Kate, A. Dudarev, and J. Buskop are with CERN, CH-1211,Geneva 23, Switzerland.Digital Object Identifier 10.1109/TASC.2005.864247Fig. 1. Cold mass pre-assembly at manufacturers works.feasibility of correct geometric assembly of coils and keystonebox modules. Following this preassembly all coils and keystoneboxes were transported to CERN.III. COLD MASS ASSEMBLY AT CERNSince delivery of the cold mass components work has com-menced at CERN to prepare modules and tooling for final coldmass assembly. Cold mass assembly at CERN is being madewith the toroid axis horizontal see Fig. 2. Planning and toolingfor cold mass assembly must be compatible with the final in-tegration of the cold mass into the vacuum cryostat. For finalintegration a large tooling and infrastructure has been set up inbuilding 191 at CERN. This will be described in Section IV.Cold mass assembly is being undertaken in four main phases:A. Preparatory Work on Coils and Keystone BoxesExtensive preparatory work has been carried out on both coilsand keystone boxes. A key part of this work has been the prepa-ration, installation and testing of cooling circuits on the coils andkeystone boxes. Aluminum cooling circuits were installed in thecoils at the fabrication stage. Since delivery, aluminum to stain-less steel transitions have been welded on all coils in order toallow final manifold connections in stainless steel. Keystone boxcooling circuits have been fabricated and installed, see Fig. 3.All circuits have undergone rigorous X-ray inspection, thermalcycling and leak testing.Coil units have been prepared for installation of quenchheaters thermal sensors, SQD’s (Superconducting QuenchDetectors) and voltage taps for quench detection and jointmonitoring.1051-8223/$20.00 © 2006 IEEE538 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 16, NO. 2, JUNE 2006Fig. 2. Cold mass assembly at CERN.Fig. 3. Installation of keystone box cooling circuits.B. Coil/Keystone Box Alignment and ShimmingWhen the coils and keystone boxes are assembled to forma complete cold mass it is important to locate the coils accu-rately at the 45 azimuthal spacing and correct radial position inorder to achieve accurate toroidal field profiles. It is also impor-tant to ensure correct mechanical connection interface betweencoils and keystone boxes, firstly, to transfer gravitational loadsand, secondly, to transfer the magnetic loads. Fig. 4 shows theload transfer points at the inner circumference. At the designstage spaces were left, 5 mm at the inner radius and 10 mm atthe outer radius. These spaces were designed to allow accurategeometric assembly taking account of the manufacturing toler-ances. In order to complete the mechanical integrity of the as-sembly and allow uniform force transfer the spaces have beenshimmed in preparation for the final assembly stage.The shim process was carried out in two stages. The coils andkeystone boxes were first aligned in a frame, see Fig. 5. In thisprocess the coils were placed at accurate 45 azimuthal andradial positions using pre-defined bushes.Fig. 4. Load transfer and shim positions at inner radius.Fig. 5. Top view on coil and keystone box alignment frame.With the coils set and the keystone box installed shim spaceswere measured at localized positions on the main flange inter-faces. This was repeated for all module positions.The second stage was to prepare the shims over the extendedflange faces. This was achieved by forming a sandwich ofthixotropic epoxy and aluminum plates and deforming thisto the correct interface thickness previously measured beforecuring the epoxy, see Fig. 6.With this preparation procedure the coils and keystone boxescan be accurately re-assembled with axis horizontal to the de-fined geometry. Final bonding with a thin resin layer will ensurehigh quality force transfer surfaces.All alignment and shim operations have been completed forthe first toroid cold mass.C. Cold Mass Geometric AssemblyA sequential build of the cold mass is now in progress. Asan initial step the first coil (lower) was assembled with its twomating keystone boxes, see Fig. 7. Other sub-assemblies of coilsand keystone boxes have been made in preparation for final as-sembly, see Fig. 8.BAYNHAM et al.: ATLAS END CAP TOROID COLD MASS AND CRYOSTAT INTEGRATION 539Fig. 6. Interface shim preparation procedure.Fig. 7. Sub-assembly of lower coil with two keystone boxes.Fig. 8. Sub-assembly of coil with keystone box showing cold mass support.For final assembly the first element will be transferred to thecold mass support frame on the toroid integration rails. Furthersub-assemblies will be added, located by special blocks and fi-nally glued and bolted at the flange interfaces. This sequencewill continue until the mid plane coils (horizontal) are in place.A dry assembly of the top half of the cold mass will then bemade. This dry assembly will allow in-situ confirmation of theFig. 9. End Cap Toroid integration infrastructure: vacuum vessel with air padsmoving on rails in front of cantilever.fit-up of the final parts in the keystone arch. Although carefulalignment of the coils was made at the shimming stage somesmall geometrical errors will remain and could affect the po-sitioning of the top coil in the arch. During this build up coilpositions will be checked by survey.When the position of the top coil is confirmed by this processfinal shim dimensions can be defined and implemented in a re-build with final gluing and bolting of all elements.When the cold mass is stripped back for rebuild of the top halfthe vacuum vessel bore tube and thermal shield will be installedin the cold mass bore.D. Instrumentation, Electrical Connection, Cooling CircuitManifoldingAs the cold mass build progresses the electrical connectionswill be made between coils. A conductor tail from each coil willbe formed across the end of the keystone box and the conductorswelded to form the low resistance connection. Thejoints will be clamped and bonded to the KSB structure to givemechanical and thermal stability.The cooling circuits, 4 per coil, 4 per keystone box, will beconnected through a stainless steel manifold system inside thekeystone box structure. All manifolds have been preformed andassembled into sub elements for final installation, this will en-sure a minimum number of in-situ welds in the keystone boxstructure. Manifold sub assemblies have been fully checked byX-ray, thermal cycling and leak testing.The cold mass will be fully equipped with instrumentation fortemperature monitoring, quench detection, joint resistance mon-itoring and quench initiation. Quench initiation will be made by2 100 W heaters on each coil. These heaters will be bondeddirectly to the conductor feed and exit from the coil. All instru-mentation is prepared and ready for installation.IV. TOROID INTEGRATIONWhen the cold mass assembly is complete the final stage willbe the toroid integration i.e. installation of the cold mass in thecryostat. Transfer of the 130 tonne cold mass into the 10 m di-ameter vacuum vessel requires a set of heavy tooling which hasbeen installed in B191 at CERN, see Fig. 9. The tooling com-prises a large cantilever beam and a pair of assembly rails whichallow the large components to be moved on air pads.540 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 16, NO. 2, JUNE 2006The cold mass will be assembled on the mid point of the railson a special support frame. When the cold mass is complete theframe with the cold mass will be moved over the large cantileverbeam. At this stage the gravity support rods will be installedto connect the cold mass and centre bore tube. With the boretube supported on the cantilever the full cold mass weight canbe transferred to the cantilever and the support frame removed.With the end plates removed the vacuum vessel can be trans-ferred over the cold mass using the rail and air pad system.At this stage axial force transfer rods will be installed andload tested. The final thermal shield end plates will be fittedand electrical and pipe work connections made into the cryostatservices turret. When this is complete turret services and vesselend plates will be fitted to complete toroid integration.V. SCHEDULEAssembly of the first cold mass for ECT A is scheduled forcompletion in November 2005. This will allow toroid integra-tion to be completed early in 2006. A pre-cooling test to 80 K isproposed before transfer to the ATLAS cavern in spring 2006.The second toroid ECT C will follow with approximately6 months interval.ACKNOWLEDGMENTWe acknowledge the contribution of many work colleaguesat Rutherford Appleton Laboratory and CERN in the realizationand integration of the ATLAS End Cap Toroids.REFERENCES[1] H. H. J. ten Kate, “The superconducting magnet system for the ATLASdetector at CERN,” IEEE Trans. Appl. Supercond., vol. 11, p. 347,2001.[2] D. E. Baynham et al., “ATLAS End Cap Toroid magnets cold massdesign and manufacturing status,” IEEE Trans. Appl. Supercond., vol.14, p. 485, 2004.[3] ——, “ATLAS End Cap Toroid magnets cryostat design, manufactureand integration at CERN,” IEEE Trans. Appl. Supercond., vol. 14, p.522, 2004.

ATLAS End Cap Toroid Cold Mass and Cryostat Integration

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