Modularity in the ATLAS upgrade strip tracker

Modularity in the Phase II Upgrade of the ATLAS Strip TrackerIan WilmutAbstractFor the phase II upgrade of the ATLAS tracker the Silicon strip tracker will be fully replaced by a larger system, which will need to be accomplished with fewer resources and on a tighter construction and installation schedule than for the current system. One measure to achieve this goal is by the use of modularity throughout the tracker project. Modularity in this context is the use of a number of identical subsystems with simple interfaces to the rest of the system. The modular objects can be produced in dedicated assembly sites and will be fully tested before being used in the next steps of the tracker integration. In this presentation we will illustrate this principle with various examples for modularity throughout the phase II strip tracker project, among which will be the local detector supports (staves/petals), the internal (type I) services and the segmentation of the evaporative cooling plant. We will demonstrate the various advantages this modular approach promises, comparing it with our experiences during the integration of the current ATLAS tracker. We will also discuss the limitations in achieving full modularity due to the finite size, geometry and local non-uniformities of the system and how they can be addressed.

What I will talk aboutWhat Modular and what we mean by modularWhere we are trying to take this approach in the ATLAS Upgrade. Examples:Service modulesStavesCooling plantWhat we did beforeWhat we are changingBenefits of a modular detectorModular vs common partsChallenges in modular construction

What the construction industry mean by modular construction.The construction industry has been exploring modular buildings for many years. In short, they aim to pre-fabricate building sections off site during the groundwork phase and then assemble the building very quickly.Building 41 at CERN and Ridgeway House at RAL were both built like this

Images from http://www.rollalong.co.uk/http://www.wikipedia.com/

What has this to do with detectors?We care about the construction time.If we rewrite the timeline on the last page for the ATLAS Upgrade it might look like this:R&D and Design FDR and procurementModule assemblyService assemblyStructure assemblyIntegrationCommissioningR&D and Design FDR and procurementModule assemblyService assemblyStructure assemblyCommissioningIntegrationTime SavingWe could save significant time building and assembling the detector if we can de-serialise the build. A modular build could de-centralise the build so we dont need an army of technicians working abroad for extended periodsA modular build could give us the chance to get really good at making things, rather than crafting them each time and knowing what we would do differently next timeWhat do we mean by modular?The dictionary doesnt help that much:OED each of a set of standardized parts or independent units that can be used to construct a more complex structureMerrium-Webster any in a series of standardized units for use togetherSo for a detector build it suggests that the system is assembled from as few similar systems as possibleThis makes sense, and for me is linked very closely to the idea of a learning curveBut for there to be real saving the modules must be minimally customised as they are assembledIn the 60s Bruce D. Henderson from BCG in Boston (management consultants) started to formalise the idea of a learning curveIn short there are significant savings in construction time as you become familiar with the task the graphs below assume a very modest 20% increase in speed for each doubling of output.The left hand graph shows the cost/time per item for a single assemblyThe graph on the right shows the total cost/time for a system of 1000 assemblies depending on the number of modules in the systemEmpirically the SCT build was about here (note item axis values are arbitrary)Ideally we want the ATLAS upgrade to be here

ATLAS context

What we can make modular and howThe modules We have long and short strip types in the barrel, and 7 types in the endcapThe staves a structure with 24 or 26 modules upon itThe services prefabricated into between 20 and 36 units per endThe cooling system10 identical cooling plants for two swappable spare plants for maintenance/disaster recovery

Modules to structures in the SCT (Barrel)

We had 2112 identical barrel modulesThe services and brackets were laid by hand onto the cylinderThe whole cylinder was populated with servicesThe modules were all mountedStructures to detector on the SCT barrel

The populated cylinders are then inserted one into the next and their services opened out.What we propose for the UpgradeThe cylinders will be exclusively mechanical devices, no services will be laid in before modules are added.Modules will be installed into a pre-built structure on individual staves containing 26 modules and all the associated services.Although we will have 12272 (6 x SCT) modules on the barrel we only have to install 472 (0.25 x SCT) staves .The services no longer need to be integrated/folded out by having a service break at the end of the cylinderStaves not modulesIntegrating all the on cylinder itemsThe key design feature of the stave is the combination of modules, cooling, electrical and optical services into one easy to install unit.All of the services are terminated at the end of the stave.The stave can be built and tested as a single unitThe stave is a pair of CFRP skins with a carbon foam/honeycomb core, a cooling pipe is embedded in the core. Kapton power tapes run the length of the stave between modules and core.

Real staves

Image on the left is a full size thermo-mechanical prototype with old design locking pointsImage below is a 4 module electrical stavelet for electrical testingPresent planning expects we will build staves 13 modules long (1.3m) housing 26 modules.Stave insertionStaves can then be slid into the cylinders and locked in placeOnce in place the tooling can be removed and the services connected.

Problems with modular stavesOne size doesnt quite fit allThe first problem on a barrel structure is the two ends (ATLAS calls them A and C)So we immediately need A and C end stavesThere are other variables as well:Long and short stripsU and V layers (variation in stereo)Orientation of locking pointsService connector orientationTo cope with this approach we are proposing a semi modular approach

ACSemi Modular stavesTop bus (straight)Temporary SMC connection for testingTemporary PPB0 connectionBottom bus (+ve or -ve)Temporary PPB0 connectionTemporary Wire bondsTop sideBottom sideFinal SMCfinal PPB0 connectionfinal PPB0 connectionFinal Wire bondsTop sideBottom sideWe will build completed staves from kits of parts that allow the stave to be configured for its exact locationWe expect 8 variants (long & short strip, A & C ends, U & V stereo)We hope this semi-modular approach will provide the benefits of modularity, but will give us the flexibility required for to meet the physics requirementsService modules not servicesSCT Service management

ATLAS Upgrade modular service management

Stave cooling pipe (in plane with stave, looped to deal with any movement during thermal contraction, include some electrical break)ID interlinkStave Connector (mounted to interlink for strain relief)Stave SM Electrical Services

CO2 ip/opFO ConnectorsSM sealing platePP1 Connectors

Installing service modules

Mechanical prototype Service Module being offered up to structure mock upService module in place with possible pipework routing at barrel end

Close up of pipe work note the identical structures coming from each service module22Number of cooling modules

Challenges in service modules designOur patch panels need to be very compact (i.e. we need a patch panel at the end of the detector)We have committed to manifolding inside the detectorAll the services need a connection at the stave/service module interfaceCooling connections will be orbitaly welded to save mass modules on staves will be multiplexed on the stave to reduce services The number of staves per cylinder is not optimal for identical service modulesService modules need to be able to be configures for a specific locationDetail on the Service ModuleWe expect between 20 and 36 service modules per end of the detectorThey will all be identical and interchangeableIn the event of service failure during the build they will be swapped out not repaired in situThe cooling pipes will manifold between 8:1 and 8:3 The electrical cables will be sorted in the service module to deliver combined services at the stave and service types at the ID patch panelThe opto will be sorted in the service module to ensure that any ribbon failures have distributed impact rather than a large local hole

Cooling plant26Cooling systemCooling is a critical infrastructure for a tracker at LHCSo far we have discussed modularity in local supports (which typically includes cooling channels/evaporators), and in services, both also part of the cooling systemWhat about the plant? Can we push the concept of modularity there as well?Note: the work on the cooling plant in the Tracker upgrade are less developed than other aspects of the tracker

27Current ATLASHere we will not discuss the various adventures we had with evaporative cooling, but the issue of modularityOne plant to cool SCT and pixels Design: 70kW at -25C, 1.1kg/s of C3F8 (6 compressors)Plant has been installed and commissioned in pit in parallel with ATLASFor R&D and assembly of detector components smaller plants have been used which were critically different from final plantFor example single-stage instead of two stage compressorsSome vital lessons could only be learned at a very late stage, the hard waye.g. mechanical stress on compressors too high in final plant

28Evaporative cooling for ATLAS UpgradeBaseline is CO2, most likely concept 2PACLChallenge is scaling from existing plants (2kW) to phase II (by factor ~100)Two stepsStep 1: scale plant capacity by factor ~10Step 2: use 10 plants in parallelExact distribution to detector not yet decided, probably split into strips and pixelsWould match 10 existing PP2 areas inside ATLAS for close-to-detector distributionApart from reducing the technical challenge of scaling, this has other benefitsCooling plants of the final size/design can be used during assembly and commissioning of tracker subdetectorsThis should help us identify any issues with the plant design or other aspects of the cooling system relatively earlyPlan to have 2 additional plants as spares/for maintenanceDesign for simple interfaces (fluid and control) for fast and arbitrary swapComplete isolation of circuits in different plants limits damage if something goes seriously wrong (contamination) SummaryBenefits of ModularReduce learning time in the build phase of a detectorMake detector elements interchangeable Failures can be replaced rather than repairedWe can afford to prototype much more of the detectorLess craft in detector build We will need less technician time at CERN for the build, the time will instead be needed at contributing institutesFull system prototype will be easier and more representativeA prototype with one service module and appropriate staves will be very close to a full system prototype this will be a very reasonable goal of a system test.The less items we have to optomise the better we will doOne significant lesson from the SCT is that to many systems were being built for the first time on the real detectorConfigurable modulesDetector physics is badly suited to 1000s of identical objects but it certainly has 10 lots of 100 similar objectsWe are aiming to build:8 flavours of staves from a standard kit of bitsUp to 72 service modules that can be configured 3 or 4 ways for different locations1 structure that can accommodate all of the variations in the staves and service modules10 cooling plants that are identical but configured and run for specific loadsJust down the road in Cowley is the Mini plant, they produce 200 000 cars a year (one every 68 seconds) one line produces 5 body styles in any order from a parts list of 6000 parts. By the definitions I use here a mini is very similar to a set of configured modules