1. Summary of thermal management meeting Summary of thermal management working group meeting, December 6 Presentations Introduction (G. Viehhauser, Oxford) Reutilisation of present tubing plant (G.V.) Status reports for different coolants: –Light fluorocarbons (G. Hallewell, CPP Marseille) –CO 2 (A. Colijn, NIKHEF) Flow control with thermostatic expansion valves (N. Hessey, FOM/NIKHEF) Recent experience from cooling system commissioning (R. Bates, Glasgow) From current cooling installation to future CS upgrade for ATLAS ID (V. Vacek, CTU, Prague) Thermal Management Issues for Stave Structures (C. Haber, LBNL)

2. Summary of thermal management meeting

3. MEANS COOLANTS

4. Summary of thermal management meeting Issues:  Try to use as much of the existing pipework as possible (mainly the tubing through the magnet to the ID volume) External components on access platforms and in USA15 can be considered less static:  Much hinges on delivery and evaporation pressure of final coolant, impedance to evacuate vapour, critical temperature of chosen fluid

5. Summary of thermal management meeting Operating temperature of silicon detectors Can we estimate a Si operation temperature for sufficient safety margin @ L>>10 34 ? From Nobu Unno’s September 6 th talk: -30°C on SCT Sensors, requiring (my guess) ~-45  C evaporation in on-detector cooling channels 15°C (Si – coolant)  T Reasonable? Conservative?...

6. Summary of thermal management meeting Power dissipation of silicon detector electronics No estimate given (anywhere in this conference) of dissipation of electronics (Given the much higher activity within the electronics + reduced radius (1/r 2 ) of new B layer, extra track / background activity at luminosities ~ 10 35

7. Summary of thermal management meeting The fluids… Two (maybe 3) candidate fluids: C 2 F 6, CO 2 & (maybe still) C 3 F 8 A few pros and cons: C 2 F 6 : Enthalpy ~ 100J/g, P evap ~ 4 bar a @ -45°C, T crit ~ 20°C Liquid delivery pressure in warm zones ≥ 30 bar CO 2 : Enthalpy ~ 280J/g P evap ~ 7 bar a @ -45°C, T crit ~ 30°C Higher evaporation pressure  higher HTC Triple point temperature ~ -56°C (dry ice formation) Liquid delivery pressure in warm zones ≥ 70 bar C 3 F 8 : Enthalpy~100J/g, P evap < 1 bar a *@ -45°C, T crit ~ 60°C * low evaporation pressure needs special treatment

8. Summary of thermal management meeting ATLAS SCT & Pixels: Principle of present C 3 F 8 system Vapour h.p. Vapour l.p. Liquid h.p. Liquid l.p. Déverseur/ Back-pressure regulator for groups of circuits (Individual P evap ) Performance squeezed here!

9. Summary of thermal management meeting Possible cycle with C 2 F 6 Surface condenser Evaporation @ -45°C: Compressor P in ~4.5bar a, P out ~15bar Detent  gh liquid return to pit Atten Attention: T crit ~20°C ΔH ~ 110 J/g

10. Summary of thermal management meeting ΔH(-35C) = 280 kJ/kg Enthalpy [kJ/kg] Pressure [bar] P = 12 bar liquid 2-phase gas CO 2 properties: p-H diagram Attention: T crit ~30°C P = 60bar Attention: P deliv ~ 60bar

11. Summary of thermal management meeting Survey of existing pipework (Georg’s thankless task…) Will incorporate ex TRT tubing into new tracker cooling plant

12. Summary of thermal management meeting Problems with the present C 3 F 8 system (Which might require ‘external’ intervention) (1)Back-pressure regulators contribute substantial (& variable) insertion loss (CV variability) being mastered…; (2) Significant insertion loss in deeply embedded hex’s, heaters;  (1) & (2)  low compressor aspiration pressure (~1bar abs ) (3) Very high compression ratio  x  across compressors due to the very high choice of condenser pressure; (1), (2) & (3) conspire to put the compressor in a regime of reduced throughput (pumping speed) and hotter operation Cooling circuits have little margin for reducing Si temperature. Also compressor cooling less efficient: (reduced flow of cooling gas)  expect a reduced MTBF? (reduced flow of cooling gas)  expect a reduced MTBF?

13. Summary of thermal management meeting HEX DCS Detector DCS Det. environmental DCS Heaters DCS Off-detector layout, inc DCS

14. Summary of thermal management meeting ATLAS pit (d ~ 92m) ATLAS Surface Buildings USA15 Remote Control Pressure regulators P in ~ 14bar (flow proportional to heat load) Compressors Condensers operating With lower input pressure than in USA15 location Tracker Example  g  h (liquid)   bar(C 3 F  ) Example:  g  h (vapour)   mbar(C 3 F  ) Toward a simplified circulator with reduced compressor stress (and enhanced compressor M.T.B.F.) Tubing to be sized for dynamic  P

15. Summary of thermal management meeting There is yet space!

16. Summary of thermal management meeting A ‘graded external fix’ approach to problems with the present C 3 F 8 system (Integrable steps in the cooling system for the tracker upgrade) APPROACH (1) Eliminate back-pressure regulators + use compressor aspiration tank pressures (by varying compressor speed using motor speed controller) to control evaporation pressure in pixel and SCT circuits Moduarity issues?

17. Summary of thermal management meeting A ‘graded external fix’ approach to problems with the present C 3 F 8 system IF APPROACH (1) DOES NOT SUFFICIENTLY INCREASE Si DETECTOR OPERATING TEMPERATURE MARGIN… APPROACH (2) Install ‘local’ (COLD  C) condensers (service platforms) Condenser cooled either using LN 2 /G    from liquid argon calorimeter cooling loops or a compressor system (R404A?) How to circulate C 3 F 8 primary coolant back to capillaries?: (2-i) Using liquid pumps (hydraulic or pneumatic drive for B field) (2-ii) Using 2 nd (external) evaporator & existing Haug Compressors in USA15

18. Summary of thermal management meeting A ‘graded external fix’ approach to problems with the present C 3 F 8 system IF APPROACH (1) DOES NOT SUFFICIENTLY INCREASE Si DETECTOR OPERATING TEMPERATURE MARGIN… APPROACH (2) Install ‘local’ (COLD  C) condensers (service platforms) Condenser cooled either using LN 2 /G    from liquid argon calorimeter cooling loops or a compressor system (R404A?) How to circulate C 3 F 8 primary coolant back to capillaries?: (2-i) Using liquid pumps (hydraulic or pneumatic drive for B field) (2-ii) Using 2 nd (external) evaporator & existing Haug Compressors in USA15

19. Summary of thermal management meeting Example of low temperature condensation (in this case C 5 F 12 /N 2 radiator gas circuit of SLD CRID) & re-evaporation Cold N 2 gas (‘conditioned’ by counterflow with boiloff LN 2 from liquid argon calorimeter) Historical: cold condenser operations

20. Summary of thermal management meeting USA15 Remote control pressure regulators P in ~ 14-17bar Haug compressors in USA15 Low temperature condenser operating on GN 2 (LN 2 boiloff) or else R404a, ex C 3 F 8 compressor system (Condenser at highest point on ATLAS platforms) Tracker Liquid pump (possibly 2-stage): Hydraulic/pneumatic drive for high B-field operation Must generate ~14-17 bar C 3 F 8 capillary input pressure 2.i Enhancing Si operating temperature margin of the present C 3 F 8 evaporative cooling system  Priming height (maximum possible)  h (liquid)  m   bar(C 3 F  ) (boosts pump output) Use Haug compressors to cool local condensers in UX (no longer in primary cooling loop)

21. Summary of thermal management meeting Principle of modified P-H cycle : recovery of present C 3 F 8 system  P (  T) between Evaporation & Condensation determined by sizing of exisiting internal services Condensation Evaporation @-45°C  P liquid via (2-stage?) pump Pressure regulators & present choice of capillary (Ø,L)

22. Summary of thermal management meeting USA15 Remote Control Pressure regulators P in ~ 14bar Haug Compressor/ condenser in USA15 Low temperature condenser operating on GN 2 (LN 2 boiloff) or else R404a, ? compressor system Tracker EVAPORATOR (2):electrically-heated evaporator pot raises the C 3 F 8 pressure sufficiently to give the USA15 compressors a higher (lower) input pressure (compression ratio), improving pumping speed & compressor cooling 2.ii Enhancing operating temperature margin of the present evaporative cooling system (2-ii) Priming height (maximum possible)  g  h (liquid)   P(C 3 F  ) EVAP(2) Local condenser cooling loop Non-return valve

23. Summary of thermal management meeting Principle of changed P-H cycle : recovery of present C 3 F 8 system  P (  T) between Evaporation & Condensation determined by sizing of exisiting internal services External evaporation 2 (P condenser1 + 3 bar?) Condensation (2): HP Gymnastics to use Haug compressors in present location with much lower compression ratio “Stave” Evaporation (1) @-45°C Condensation (1): LP Gravity head between Condenser 1 (platform?) & Evaporator 2 (pit floor?)

24. Summary of thermal management meeting Clearly… The system is not energy-efficient  the coolant makes 2 closed loops for one cycle; ! However one should not forget this is an external fix to give more evaporating temperature margin to a borderline system and to allow the tracker to operate in the interim with C 3 F 8 until the cooling can be correctly reconfigured internally and externally

25. Summary of thermal management meeting Fluorocarbons can be mixed (blended ) to arrive at compromise thermodynamic properties (many modern refrigerants are blends)  This was tested with C 3 F 8 /C 4 F 10 (2 papers in Fluid Phase Equilibria 2000-2001) Mixture thermodynamic, transfer properties calculated & set up as ‘temporary’ folders in NIST database verified by measurement (sound velocity in superheated phase)

26. Summary of thermal management meeting CO 2 Status report A. Colijn, NIKHEF CO 2 : Why? CO 2 : Cooling system for LHCb vertex detector CO 2 : Research plans at NIKHEF

27. Summary of thermal management meeting ΔH(-35C) = 280 kJ/kg Enthalpy [kJ/kg] Pressure [bar] P = 12 bar liquid 2-phase gas CO 2 properties: p-H diagram Attention: T crit ~30°C

28. Summary of thermal management meeting LHC-b ‘VELO’ vertex tracker CO 2 cooling system: (NIKHEF) Fully assembled under testing Installed nowUnder construction VELO areaCooling plant area detectors

29. Summary of thermal management meeting VTCS cooling cycle

30. Summary of thermal management meeting LHCb: Mechanical construction Accumulator CO2 pumps Heat exchanger Automatic valves FRONT BACK

31. Summary of thermal management meeting NIKHEF & CO 2 : Cooling plant Test setup Compact CO 2 cooling plant Primary CO 2 cooler Accumulator Condensor Pump Heat exchanger Secondary CO 2 circulation circuit Compressor (with oil) condensor Detector

32. Summary of thermal management meeting

34. USA15: C 3 F 8 compressors Back-pressure regulator rack: setting of evaporation pressure (temperature) (64 / 324 circuits)

35. Summary of thermal management meeting

36. ATLAS Internal cooling system (thanks to Richard Bates’ presentation, September 6 2006)  Two problems: Membrane valve & v.p. bulb need to be directly across evaporator only (NOT evaporator AND sub-cooling Hex: or hard-to-damp oscillations can occur) This means in high radiation field of ID volume: problems with materials used in valve…

37. Summary of thermal management meeting Infrastructure at CPPM

38. Summary of thermal management meeting

39. GUI in PVSS II Finite state machine in PVSS to send fluid through pixel ladder by sequencing pneumatic valves

40. Summary of thermal management meeting GUI in PVSS II Machine a état finie pour envoyer fluide vers l’échelle séquencing des vannes pneumatiques Part of a run of 1000 heat/cool cycles (Accelerated Thermal Stress Test of thermal interfaces in a pixel stave)

41. Summary of thermal management meeting New compressor at CPPM : capacity = 4kW PID controllers Condensor Aspiration buffer