Baynham, D E

Benoit, P

Buskop, J

Carr, F S

Dudarev, A

Holtom, E

Pengo, R

Ruber, R

ten Kate, H H J

Vandoni, G

D. Elwyn  Baynham

Herman H.J. Ten Kate

F. Steve Carr

Edward Holtom

Jarl Buskop

Alexey Dudarev

Philippe Benoit

Giovanna Vandoni

Roger Ruber

Ruggero Pengo

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ATLAS End Cap Toroid Integration and Test

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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007 1197ATLAS End Cap Toroid Integration and TestD. Elwyn Baynham, F. Steve Carr, Edward Holtom, Jarl Buskop, Alexey Dudarev, Philippe Benoit,Giovanna Vandoni, Roger Ruber, Ruggero Pengo, and Herman H. J. Ten KateAbstract—The ATLAS Experiment at LHC, CERN will utilizea large, superconducting, air-cored toroidal magnet system witha long Barrel Toroid and two End Cap Toroids. Each End CapToroid will contain eight racetrack coils mounted as a single coldmass in a cryostat vessel of approximately 10 m diameter and 5 mwidth. The toroids provide the magnetic field for the muon detec-tors. The operating current is 20.5 kA at 0.25 GJ stored energy anda peak field of 4.1 T in the windings. This paper presents the statusof the End Cap Toroid Project. Cold mass assembly and the inte-gration of the full cold mass, 120 tons, into the vacuum cryostat forthe first toroid are described. The specialized techniques, proce-dures and tooling infrastructure required for these operations areexplained. The pre-installation cooldown to 77 K at the ATLAScryogenic test facility is reported and the toroid installation in theATLAS Experiment 100m underground in the ATLAS cavern willbe reviewed.Index Terms—Detector magnet, superconducting, toroidal field.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).The twoEnd Cap Toroids are designated ECTA and ECTC accordingto their position in the ATLAS experiment. The major featuresof the End Cap Toroid Magnets have been described elsewhere[2]. Each ECT consists of a cold mass, eight superconductingcoil modules and eight keystone boxes, mounted in a largecastellated cryostat [3]. The cold mass will be directly cooledby pumped circulation of two phase helium. All services willbe carried through a single turret. In this paper we describe theassembly of the two cold masses at CERN and the integrationof the first full cold mass into the vacuum cryostat to form thefinal toroid assembly of ECTA. The planning and infrastructurefor pre-installation cooldown to 77 K at the ATLAS test facilityis described.II. COLD MASS ASSEMBLYThe Cold Mass consists of eight superconducting coils andeight keystone box (KSB) modules. The keystone box modulesManuscript received August 25, 2006. This work was funded by the ATLASCollaboration, NIKHEF and CERN.D. E. Baynham, F. S. Carr, and E. Holtom are with the CCLRCRutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, UK (e-mail:e.baynham@rl.ac.uk).J. Buskop is with NIKHEF, 1009 DB Amsterdam, the Netherlands.A. Dudarev, P. Benoit, G. Vandoni, R. Ruber, R. Pengo, and H. H. J. Ten Kateare with CERN, CH-1211, Geneva 23, Switzerland.Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TASC.2007.897734Fig. 1. Cold mass assembly concept at CERN.are the structural elements that maintain the toroidal shape undergravitational and magnetic loads. The cold mass componentswere manufactured by BRUSH HMA BV in the Netherlandsunder a contract placed by NIKHEF, Amsterdam. Coil and key-stone box fabrication has been described previously [2].Cold mass assembly at CERN has been made with the toroidaxis horizontal, see Fig. 1. Cold mass assembly was undertakenin three main phases.A. Preparatory Work on Coils and Keystone BoxesExtensive preparatory work was carried out on both coils andkeystone boxes. A key part of this work was the preparation,installation and testing of cooling circuits. A dual cooling circuitsystem is installed to minimize the impact of any leak in coolingcircuit component.Aluminum cooling circuits were installed in the coils at thefabrication stage and bonded into the structure during coil im-pregnation. After delivery to CERN aluminum to stainless steeltransitions were welded on all coil circuits in order to makefinal connections to the stainless steel distribution manifold.Cooling circuits were fabricated and installed in the keystoneboxes. Circuits were subjected to rigorous x-ray inspection,thermal cycling and leak testing before release to the cold massassembly process. Coil units were prepared for installationof quench heaters, thermal sensors, superconducting quenchdetectors (SQDs) and voltage taps for quench detection andjoint monitoring.When the coils and keystone boxes are assembled to forma complete cold mass it is important to locate the coils accu-rately at the 45degree azimuthal spacing and correct radial po-sition in order to achieve accurate toroidal field profiles. It isalso important to ensure a correct mechanical connection inter-face between the coils and keystone boxes, firstly, to transfergravitational loads and secondly, to transfer the magnetic loads.1051-8223/$25.00 © 2007 IEEE1198 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007Fig. 2. Keystone arch force transfer concept showing shim location.Fig. 2 shows the load transfer concept at the inner circumfer-ence. At the design stage spaces were left between the coilsand the keystone boxes, 5 mm at the inner radius and 10 mmat the outer radius. These spaces were designed to allow accu-rate geometric assembly taking account of the manufacturingtolerances. In order to ensure the mechanical integrity of theassembly and allow uniform force transfer the interfaces wereshimmed in preparation for the final assembly stage.The shim process was carried out in two stages. The coilsand keystone boxes were first aligned in a frame with the toroidaxis vertical. In this process the coils were placed at accurate 45degree azimuthal and radial positions using survey bushes. Withthe coils set and the keystone box installed shim spaces weremeasured at localized positions on the main flange interfaces.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 (a gel epoxy which flows freely under pres-sure) and aluminum plates and deforming this to the correctinterface thickness previously measured before curing theepoxy.With this preparation procedure the coils and keystone boxescould be accurately re-assembled with axis horizontal to the de-fined geometry. Final bonding with a thin resin layer ensuredhigh quality force transfer surfaces. This work has been com-pleted for both cold masses.B. Cold Mass Geometric AssemblyA sequential build of the cold mass for ECTA was made onthe toroid integration rails. As an initial step the first coil (lower)was assembled with its two mating keystone boxes.Further sub-assemblies of coils and keystone boxes weremade in preparation for final assembly. These sub-assemblieswere added sequentially, located by special blocks and finallyglued and bolted at the flange interfaces. This process con-tinued until the mid plane coils (horizontal) were in place. Adry assembly of the top half cold mass sub-assemblies wasthen made. This dry assembly allowed in-situ confirmation ofthe fit-up of the final parts in the keystone arch. During thisbuild up coil positions were checked by survey.The top halfof the cold mass pre-assembly was then stripped back and thevacuum vessel bore tube and thermal shield installed in theFig. 3. Full assembly of cold mass on integration rails.cold mass bore. The final step in the assembly process was there-positioning, final gluing and bolting of all elements in thetop half of the cold mass assembly. At this stage final blockingand bolting at all flange interfaces was made. Fig. 3 shows thefinal mechanical assembly of ECTA cold mass mounted onthe rail infrastructure in the integration hall.The preparationsfor final assembly of ECTC cold mass have proceeded inparallel in an adjacent building. With the knowledge gainedfrom the first assembly the procedure for the second cold masswas modified to allow maximum pre-assembly and minimumfinal assembly work on the integration rails at high level. Thisprocess has been based on the full pre-assembly of the top andbottom halves of ECTC cold mass. These will be transportedto the integration rails as complete units. The half-assembliesalready have the main cooling circuit manifolds installed andthe conductor joints between coils fabricated. This will reallyshorten the final assembly steps on the integration rails.C. Instrumentation, Electrical Connection, Cooling CircuitManifoldingAs the build of cold mass ECTA progressed the electrical con-nections were made between coils. A conductor tail from eachcoil was formed across the end of the keystone box and the con-ductors welded to form the low resistance connection. The jointswere clamped and bonded to the KSB structure to give mechan-ical and thermal stability.During the cold mass build the cooling circuits, 4 per coil, 4per keystone box were connected through a stainless steel man-ifold system inside the keystone box structure. The manifoldswere pre-formed and assembled into sub-elements for final in-stallation to ensure a minimum number of in-situ welds in thekeystone box structure. All circuits were successfully pressureand leak tested.The cold mass has been fully equipped with instrumenta-tion for temperature monitoring, quench detection, joint resis-tance monitoring and quench initiation. Quench initiation willbe made by 2 100 W heaters on each coil. These heaterswere bonded directly to the aluminum stabilized conductor atthe feed/exit from each coil.BAYNHAM et al.: ATLAS END CAP TOROID INTEGRATION AND TEST 1199Fig. 4. Integration of vacuum vessel shell over cold mass. Cold mass supportedon cantilever beam. Vessel shell supported by large structure frame on integra-tion rails.III. TOROID INTEGRATIONToroid Integration comprises 4 main steps; transfer of thecomplete cold mass onto the large cantilever beam and loadingfrom the gravity support rods; movement of the outer vacuumvessel shell over the cold mass to allow connection of axial forcetransfer rods and thermal shield end plates; installation of finalinstrumentation and the services turret; closure of the vessel endplates and transfer of the overall load to the rails. Transfer ofthe 130 ton cold mass into the 10 m diameter vacuum vessel re-quires a set of heavy tooling which was pre-installed in B191at CERN. The tooling comprises a large cantilever beam and apair of assembly rails which allow the large components to bemoved on air pads. This section describes the main integrationsteps and the status.A. Transfer Onto the CantileverThe cold mass was assembled on the mid point of the railson a special support frame. When the cold mass was completethe frame with the cold mass was moved over the large can-tilever beam using air pads. At this stage the gravity support rodswere installed to connect the cold mass and center bore tube.The gravity support rods are fabricated in stainless steel witha main section 60 mm by 125 mm. In operation each rod willcarry a load of approximately 40 tons. The rods are connectedto a special saddle on the vacuum bore tube and a bracket onthe keystone box through rotating ball ends. With the bore tubesupported on the cantilever the full cold mass weight was trans-ferred to the cantilever and the support frame removed. Duringthis process the deflection of the cantilever was compensatedby jacks to maintain the axis of the cryostat bore tube hori-zontal. The whole process required very careful alignment of thecold mass to ensure equal loading of the gravity support rods.Through this adjustment a load sharing of better than 10% wasachieved. Fig. 4 shows the full cold mass of ECTA mounted onthe cantilever.B. Integration With Outer Vessel Shell and AFT RodsBefore transferring the cold mass onto the cantilever frameone vacuum vessel end plate was transferred to the inner part ofthe cantilever frame to be available for final vessel closure.The outer vessel shell was then transferred over the cold massusing the rail and air pad system. During this operation thebasic shape of the outer shell was maintained by a large externalframe, see Fig. 4 which shows the outer shell positioned over thecold mass.In operation the cold mass of each ECT will experience anaxial force of approximately 280 tons towards the center of theexperiment due to the interaction with the Barrel Toroid (BT)field. Within the ECT cryostat this force is transferred to thevacuum vessel shell by 16 axial force tie (AFT) rods. Each rod isconnected to the cold mass keystone box and to a special bracketon the inside of the vacuum vessel shell. On the outer surface ofthe vacuum vessel shell a bracket will be installed to react thisload to the BT coil cryostats. The shape of the vessel shell and itsalignment with the cold mass axis and the vessel bore tube wascritical for the correct setting of the AFT rod lengths. Distortionsof the vessel after set up could lead to large stresses in the AFTrod system and by linkage give unequal loading in the gravitysupport rod system. It was found that the outer shell shape wasdifficult to control to a tolerance better than 20 mm without theend plates of the vessel closed and fixed by the dowel system.Such errors were sufficient to give problems with final AFT rodset up. After extensive analysis and manipulation of the vesselshell it was decided to implement a system to allow adjustmentof the AFT rods after closure of the vessel end plates and whicheven allows adjustment after cooldown. In such a way assemblyerrors, mounting errors and any differential cooldown errors canbe eliminated. This modified system is under implementation.C. Installation of Thermal Shields and Services TurretThe thermal shield and superinsulation components were pre-installed in the vacuum vessel shell as a first stage of integration.The completion of the thermal shield system involves the instal-lation of stay tube shields, the shield end plates and the con-nection of all elements, see Fig. 5. The cooling of the thermalshields is provided by dual circuits attached to each end plate.The bore tube, stay tube and outer shell shields are cooled byconduction from the end plates. The shield end plates are fab-ricated as two half plates which will be finally closed by coilcover plates.The half endplates have been installed using specially de-signed tooling to handle the components which measure approx-imately 10 m by 5 m, see Fig. 5. Installation of the stay tubeshields and the thermal and mechanical connections to the endplate cooling is in progress.All services to the ECT’s are connected through a single turretmounted on the top vacuum vessel castellation. The turret struc-ture consists of an outer shell, a large top plate and a sealingring to complete the vacuum integrity. The system is designedto allow installation of the top plate with all components beforeclosing with the outer shell and the sealing ring. Current con-nections are made through two 20 kA current leads mountedthrough the top plate on a bellows system to accommodate thecooldown shrinkage of the cold mass. Cryogenic connections1200 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007Fig. 5. Installation of end plate thermal shields.are made through a single vacuum barrier system which will in-corporate liquid helium feed and return circuits at 4.5 K in ad-dition to helium gas feed and return circuits cooling the thermalshield system at 40 K and 80 K respectively. The ports whichwill carry the instrumentation interface plates are also mountedon the top plate. Two diffusion pumps will be mounted on op-posing sides of the turret shell.A full pre-build of the top plate with all components fitted wasmade at ground level to minimize the amount of assembly workto be undertaken at the top of the vacuum vessel. The top plate,with all components, has been lifted into position and work isin progress to make the final connections to the coil conductortails and the various cooling circuits. At this stage the final con-nections to instrumentation in the vessel are being made. Whencomplete the turret vessel will be closed by fitting the outer shellequipped with the vacuum pumps.D. Final Integration Closure of VesselThis is a complex task which requires installation of the vesselstay tubes, the interfacing to the bore tube of the vessel and theouter shell. Final mechanical closure involves the installation of96 large dowels in each end plate. The dowels will transfer thevacuum loads (750 tons) from the outer shell to the endplate andlocate the two parts to better than 0.1 mm. When the end platesare fitted the vacuum integrity will be checked by pumping be-tween the double o-ring system.When the vessel is complete the full toroid will be transferredfrom the cantilever to the rail system using jacks and air-pads.The toroid can then be prepared for transport to the test station.IV. PREPARATION FOR TEST AND INSTALLATIONA cooldown of each toroid to 77 K will be made before in-stallation. The test will be carried out at the ATLAS cryogenictest facility previously used to test and commission the ATLASBarrel Toroid coils. This test will confirm the correct operationof vacuum systems, cooling circuits and instrumentation. Fullleak checking and voltage testing will be carried out. The infra-structure for cooldown and test is close to completion.When the toroid is installed in the ATLAS cavern the ser-vices; cryogens, vacuum, power and instrumentation, will beconnected to the top level of the ATLAS experiment through aservices tower approximately 5 m in height. The tower design iscomplete and the flexible chain to connect to the fixed services atthe side of the ATLAS cavern is under procurement. The chainsystem will allow the services to remain connected to the EndCap Toroid when the magnet is moved from the beam positionto allow access to the inner part of the ATLAS experiment.V. SCHEDULEIntegration of the first Toroid ECTA is scheduled for com-pletion in September 2006. A pre-cooling test to 77 K will beperformed before transfer to the ATLAS cavern in late 2006.The second toroid, ECTC, will follow with approximately sixmonths interval.ACKNOWLEDGMENTThe authors acknowledge the contributions of many col-leagues and co-workers at CERN and the Rutherford AppletonLaboratory.REFERENCES[1] H. H. J. Ten Kate, “The ATLAS superconducting magnet system:Status of construction and installation,” IEEE Trans. Appl. Supercon-ductivity, vol. 16, p. 499, 2006.[2] D. E. Baynham et al., “ATLAS End Cap TOROID magnets cold massdesign and manufacturing status,” IEEE Trans. Appl. Superconduc-tivity, vol. 14, p. 485, 2004.[3] D. E. Baynham et al., “ATLAS End Cap Toroid cold mass and cryo-stat integration,” IEEE Trans. Appl. Superconductivity, vol. 16, p. 537,2006.

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