Thermal management for ATLAS upgrade Georg Viehhauser 30/10/082 Organisation Common understanding that thermal management in ATLAS has been more painful than necessary. Thermal management comprises High thermal conductivity materials (this is the aspect which did belong to subsystem designs and has worked out well), Cooling (external plant and on-detector components like HEXs and heaters, services like pipes and fittings, etc.), Environment (thermal enclosure, humidity incl. monitoring, etc.). Attributed to absence of any coordinated management structure & lack of effort until late in production. For upgrade: Thermal management working group established as first subgroup of the upgrade project office. 30/10/083 (Original) remit of the TMWG Cooling technology Quick agreement: go evaporative again Various candidate coolants: Fluorocarbons (C 3 F 8, C 2 F 6 ) or CO 2. Address issues like Control: Fixed vs variable mass flow. Throttling Pipework and Fitting specification Test facility design and manufacture During ATLAS assembly several C3F8 have been built in parallel with very different designs duplicate efforts Environment Thermal enclosure Humidity environment Monitoring Cooling system Environment Materials including thermal interfaces This is now covered by the subdetector collaborations. 30/10/084 Key requirements About 10colder than present ATLAS ID(coolant temperature -35C instead of -25C) ~2 power of present ATLAS ID(~ kW instead of 60kW), increase in size and channel density, but reduction of power per electronics channel. About 800 supermodules/staves. High reliability and robustness against failures. Failures should not affect large sections of experiment. Access to complex objects (HEXs, heaters, etc.) 30/10/085 Coolant options C 3 F 8 By 2017 we have ~10y of operational experience. Reduce start-up hiccups if we can develop an adiabatic upgrade plan. But: It is not clear that a pure C 3 F 8 system can achieve the evaporation temperature. T evap = T(p evap ) and p evap = p suction + p pipe + p bpr We have to address this already for the existing system. Various strategies under consideration: Lower p suction : surface condensers, multi-stage compressors, Avoid p bpr : evaporation pressure control through cold condensers, Lower T(p evap ): Use C 2 F 6 /C 3 F 8 mixtures. CO 2 Expect smaller mass flow (large latent heat), smaller pipes (large HTC), albeit probably thicker wall. Higher pressures (p max ~50-100bar a, p evap ~10bar a ). Not a fundamental problem, but needs careful engineering. No danger of restricting environmental legislation. Industrys future coolant of choice. The decision needs to be made soon (impact on detector design). 30/10/086 A major constraint for ATLAS upgrade Reuse existing services running from z=0 (outside calorimeters) to end of calorimeter to reduce shutdown time. These services run underneath innermost layer, which should not be disturbed to shorten shutdown. This has never been formally evaluated and decided (too complex), but became widely accepted. This provides a limitation In diameter and number (issue for C 3 F 8 : limits possible reduction in return line pressure drop). Due to pressure specification (issue for CO 2 : present Cu/Vulkan Lokring pipework only good to 30 to 50bar a ). Due to lack of insulation: transfer pipes need to be warm (above dewpoint ~15C), conservative estimate: feed 35C due to environment (cables), this increases the input vapour quality reduces the available latent heat increased system complexity (requires pre-cooling HEXs, requires heaters) and drives up the feed pressure for coolants with low critical pressure. 30/10/087 ID A possible solution: multi-stage system Primary (plant) stage: Conventional (oily?) Compressor-condensor- throttle-evaporator system. Technology (coolant) is flexible. This has warm transfer pipes (if CO 2 with high feed pressure ~100 bar a ). Evaporates at ~ -40C. Return lines have electrical heaters (accessible) to keep return fluid warm. Secondary (detector) stage: Condensor-pump-evaporator This would have cold, low-pressure lines. Condenses at ~ -40C, evaporates at ~-35C. While in principle you dont need a throttle (capillary), it will be required for control of the circuit and flow balancing. To minimize mass flow (pipe diameter) the coolant in this stage will be CO 2. Thermally connected by HEX at PP2 Throttling, back pressure regulation and heater close to HEX accessible (~1d) and moderate radiation. Calorimeter Inner muon Middle muon Access Conceptual, not to scale detector Q Q Q 30/10/088 Pipework In ATLAS Poorly evaluated technologies and procedures, Aluminium pipes: corrosion problems due to alloy choice and handling mistakes, Home-made connections developing leaks. Poorly specified leak-rate requirements, Varying from section to section. Learned a lot about QA too late E.g. X-rays of welds etc. Upgrade: Develop a coherent set of specifications for all components, Specifications for components where possible (base on industrial standards where possible), Definition of specification procedures for new (homemade) solutions, Ultimately possibly specifications of components (fittings, etc.), This specifications (components and procedures) should be used at all stages of the project (design, assembly, commissioning, running), This task is formidable, but could/should be of wider interest. 30/10/089 Risk analysis In the past Done late with insufficient resources and expertise has been usually a fault mode analysis, not a risk analysis. often retroactive, not part of design decisions. Should be Expanded to reliability analysis and as such should influence design. Will need to learn a lot about this 30/10/0810 Future organization So far there has been a split into present system and sLHC upgrade. In the future there will be global ATLAS structure on cooling including Current system operation, Improvements to current system to reach ATLAS final specifications, Cooling for the insertable B-layer (innermost Pixel), ID cooling for sLHC upgrade. Details are being worked out right now. Sharing of resources, brainpower and information needs to be organized. 30/10/0811 Some cooling contacts in ATLAS Rather than listing all groups and individuals I will list a few contacts which then can guide you on. Present system operation: Steve McMahon, Koichi Nagai, C 3 F 8 upgrades: Greg Hallewell, CO 2 cooling: Bart Verlaat, Nigel Hessey, Pipes and connectors: Jason Tarrant, CF pipes: Danilo Giugni. Backup slides 30/10/0813 From Auke Colijn 30/10/0814 From Vic Vacek 30/10/0815 From Vic Vacek