1. 1 GL-2008 8th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids Bart Verlaat National Institute for Subatomic Physics (NIKHEF) Amsterdam, The Netherlands CO 2 COOLING FOR THE LHCB- VELO EXPERIMENT AT CERN CDP 16 - T3-08 Copenhagen, 9 September 2008

2. 2 Table of Contents Introduction to Particle Physics research, NIKHEF and CERN. Introduction to the LHCb and the VELO detector. Explanation of the VELO Thermal Control System (VTCS). Commisioning results of the VTCS. Conclusions and outlook.

3. 3 Introduction to Nikhef National Institute for Subatomic Physics Amsterdam, the Netherlands Alpha Magnetic Spectrometer on the International Space Station The Large Hadron Collider related experiments at CERN in Geneva 27 km Ca. 100m Nikhef participates in particle physics experiments world- wide: –Particle accelerator experiments –Astro-particle physics experiments Goals of the particle physics research: –What is matter made of? –How do forces work? –Where did matter come from? Starts tomorrow! (Details at the end) LHC ISS

4. 4 Electron Hadron Proton beam LHCb Detector Overview Muon LHCb Cross section Goals of LHCb: Studying the decay of B-mesons to find evidence of CP-violation (Why is there more matter around than antimatter?) 20 meter Vertex Locator

5. 5 VELO Thermal Control System CO 2 evaporator section Detectors and electronics 23 parallel evaporator stations capillaries and return hose Temperature detectors: -7ºC Heat generation: max 1600 W The LHCb-VELO Detector (VErtex Locator)

6. 6 22 August 2008 The VELO has seen particle tracks from an LHC test! The Velo Detector Heat producing electronics CO 2 evaporator (Stainless steel tube casted in aluminum) Detection Silicon

7. 7 VELO Cooling Challenges VELO electronics must be cooled in vacuum. –Good conductive connection –Absolute leakfree Maximum power of the electronics: 1.6 kW Silicon sensors must stay below -7°C at all times (on or off). –To avoid thermal runaway of the irradiated silicon Adjustable temperature for commisioning. Maintenance free in inaccessable detector area

8. 8 The 2-Phase Accumulator Controlled Loop (2PACL) 2PACL principle ideal for detector cooling: -Liquid overflow => no mass flow control -Low vapor quality => good heat transfer -No local evaporator control, evaporator is passive in detector. -Very stable evaporator temperature control at a distance (P 4-5 = P 7 ) Condenser Pump Heat exchanger evaporator Restrictor 2-Phase Accumulator Heat in Heat out 1 23 4 5 6 Liquid Vapor 2-phase Enthalpy Pressure 1 23 4 5 6 P7P7 P7P7 P 4-5 Long distance

9. 9 VTCS Accumulator Control Thermo siphon heater for pressure increase (Evaporation) Cooling spiral for pressure decrease (Condensation) Accumulator properties: Volume: 14.2 liter (Loop 9 Liter) Heater capacity: 1 kW Cooler capacity: 1 kW System charge: 12 kg (@23.2 liter) System design presure: 135 bar + + + _ + _ Heating Cooling Setpoint Temperature Temperature Pressure Evaporator Pressure Pressure drop PID P set T set P accumulator ΔP fault

10. 10 3.6 m 2.6 m 2 R507A Chillers: 1 water cooled 1 air cooled 2 CO 2 2PACL’s: 1 for each detector half 55 m Accessible and a friendly environment Inaccessible and a hostile environment 2 Evaporators 800 Watt max per detector half VELO LHCb-VTCS Overview (VELO Thermal Control System) PLC 2 Concentric transfer lines 4m thick concrete shielding wall

11. 11 VTCS Schematics 2x CO 2 2PACL’s connected to 2 R507A chillers (Redundancy) Lots of sensors and valves

12. 12 LHCb-VTCS Cooling Components VTCS Evaporator Pumps Accumulators Condensers Valves

13. 13 VTCS Units Installed @ CERN July- August 2007 CO 2 Unit Freon Unit

14. 14 VTCS 2PACL Operation From start-up to cold operation (1) Start-up in ~2 hours A B C D time 14 2 Pump head pressure (Bar) 4 - Accumulator pressure (Bar) 1 Pumped liquid temperature (°C) 5 – Evaporator temperature (°C) 4-Accumulator liquid level (vol %) 4- Accumulator Control: + = Heating - = Cooling _ + 4 1 2 7 7 7 7 1 2 7 4 +7 -7

15. 15 Accumulator Cooling = Pressure decrease VTCS 2PACL Operation From start-up to cold operation (2) A B C D Start-up in ~2 hours A B C D time 15 2 - Pump head pressure (Bar) 4 - Accumulator pressure (Bar) 1 – Pumped liquid temperature (°C) 5 – Evaporator temperature (°C) 20 °C 0 °C -20 °C -40 °C 1 2 4 A B C D Path of 5 4 4 1 2 5 2 5 4 1 5 5 Enthalpy Pressure Set-point range

16. 16 March ’08: Commisioning of the VTCS Detector under vacuum and unpowered

17. 17 SP=-25°C SP=-5°C (3 sept 08) Accu level Module Heat load Silicon temperature Evaporator temperature Accu Heating/Cooling 24 June ’08: After a succesful commisioning of the detector at -25°C, the setpoint is increased to -5°C. And has been running since then smoothly! 80 60 40 20 0 -20 -40 0 0:30 1:00 1:30 2:00 Time (Hour) Temperature (°C), Power (Watt), Level (vol %) Detector half heat load (x10) -7°C

18. 18 CO 2 liquid dT=4.5°C Cooling block dT=0.04°C 1 hour Evaporator Pressure 31.15 bar = -4.18°C Cooling block temperature = -2.8°C CO 2 liquid temp= -42°C Evaporator liquid inlet temp = -4.40°C Evaporator vapor outlet temp = -4.44°C Accumulator Pressure 30.54 bar = -4.90°C Detector offset from accu control: 0.7°C CO 2 heat transfer dT=1.4°C VTCS performance overview for a setpoint of -5°C (Detector switched on, fully powered) dP=0.6 bar = 6.2 m static heigth Fluctuations from the untuned chiller

19. 19 Summary The VTCS has successfully passed the 1 st commissioning phase and is ready to be used in the experiment Operational temperature range is between 0°C and -30°C set point It has run for 2½months continuously without any problem It behaves very stable (<0.1°C fluctuation), with the chiller still to be tuned. The silicon temperature is below the required -7°C @ -25°C set point temperature. (This is consistent with the prediction) Lessons learned The accumulator sometimes gives the pump a 2-phase mixture => cavitation. Problem is solved by connecting the accu to the inlet of the condenser instead of the outlet where it is now. Operational temperature range of the evaporator is larger than expected. This is due to the “Duck Foot Cooling 1 ” principle of the transfer line. Next time we keep the system more simple, adding redundancy is not always adding reliability……… 1 The way a duck can have cold feet without loosing body heat, by exchanging heat between the in- and outlet bloodstream.

20. 20 Outlook The VTCS is not yet finnished, some things have to be done: –Implementing automatic back-up procedure. –Changing the accumulator connection. –Tunning the chiller. –Analyse data for publication. Other CERN detectors (Atlas/CMS) have shown interest in the VTCS for their inner tracker upgrades. –Challenge: Scaling of the 1.6kW VTCS to a 100kW system. –Bigger chalenge: Convince a few hundred physists to do so. Construction of a mini desktop 2PACL CO 2 circulator for general purpose laboratory use.