1. A.P.Colijn1 CO2 Cooling for an ATLAS upgrade Plant requirements CO 2 : Properties CO 2 : Consequences of the properties CO 2 : From LHCb to ATLAS (or the CO2 conspiracy)

2. A.P.Colijn2 Requirements for ATLAS 1.Cool many distributed heat sources spread over large volumes 2.Low material in the detector 3.Small temperature gradients over long distances 4.Radiation hard 5.Reliability Will try to convince you that CO 2 has it all!

3. A.P.Colijn3 ΔH(-25C) = 280 kJ/kg Enthalpy [kJ/kg] Pressure [bar] P = 17 bar liquid 2-phase gas CO2 properties: p-H diagram

4. A.P.Colijn4 C3F8 properties: p-H diagram ΔH(-25C)=100 kJ/kg P = 1.7 bar liquid 2-phase gas

5. A.P.Colijn5 Run conditions @ -25C C3F8C3F8 CO 2 P evaporation 1.7 bar17 bar ΔT for ΔP=+-0.1bar+1.4 C / -1.5C+0.2 C / -0.2 C ΔT for ΔP=+-1.0bar+12 C / ~-20 C+1.8 C / -1.9 C ΔH for evaporation100 J/g280 J/g Flow for 100 W1.0 g/sec0.4 g/sec Volume flow0.6 cm 3 /sec0.4 cm 3 /sec Major difference for CO2 with respect to C3F8 cooling is the increase by a factor of 10 of the evaporation pressure for T=-25C.

6. A.P.Colijn6 High Pressure CO2 plant must be able to withstand about 100bar (C3F8 in ATLAS 20bar) + low temperature gradients (dP/P small because P is high) + low tube diameter (because we can allow large dP) + low tube thickness (because of low tube diameter) + high tube flexibility (reduce mechanical stress) - need more pipe at your heat sinks - higher pressure = higher tube thickness Some b.o.e. calculations to follow to get some feeling for the numbers….

7. A.P.Colijn7 Back-of-the-envelope-calculation What design consequences would it have to replace C 3 F 8 with CO 2 ? Calculations assume CuNi pipes, just as for SCT Cool approximately 100W / cooling loop Disclaimer: –calculations need more refinement –calculations must be supported by measurements

8. A.P.Colijn8 Pipe diameter: pressure drop ΔPΔP=pressure drop FmFm =mass flow η=viscosity R=pipe radius L=pipe lenght Pressure drop for a 1g/sec CO2 flow is of the order of 0.08 bar. Even with a factor 10 more flow temperature differences of a couple of degrees can be expected! Assume a pipe diameter of 0.9mm, which is 1/4 th of the C3F8 cooling pipes we have now on the SCT endcap

9. A.P.Colijn9 Pipe diameter: pipe thickness d=pipe diameter T=pipe wall thickness S=tensile strength P max =max pressure With the same pressure as in the C 3 F 8 system we could reduce the pipe thickness by a factor four A CO 2 system has to withstand much higher pressure, so we have to multiply the pipe thickness again by a factor of six T = 0.12 mm

10. 10 Material: CuNi pipes for CO 2 and C 3 F 8 d=3.6mm T = 0.07mm I: CuNi for CO 2 at 100 bar d=0.9mm T = 0.12mm II: CuNi for C 3 F 8 at 20 bar

11. A.P.Colijn11 SCT EndcapA disk1 Low diameter piping is much more flexible: goes like R 5. So no “funny” bends needed in your structure to absorb mechanical stress. Pipe flexibility: stress

12. A.P.Colijn12 Heat absorption P = required cooling power H = heat transfer coefficient in Wm -2 K -1 (calculate/measure it… O(5000Wm -2 K -1 ) d = pipe diameter ΔT=change in temperature To absorb 10W you would need 4 cm of large diameter CuNi pipe, versus 14 cm small diameter pipe if CO2 is used……. Solutions R&D: - “snaky” cooling pipes at cooling contact - large contact area with module - or….

13. A.P.Colijn13 CO 2 : From LHCb to ATLAS 1.Carbon copy the LHCb plant –(by then) tested technology –“Cold” input lines –Relatively small return lines 2.Design single-stage freezer –“Warm” input lines –Need oil-less CO 2 compressor (!) –Need relatively big return lines

14. A.P.Colijn14 Enthalpy [kJ/kg] Pressure [bar] liquid 2-phase gas CO2 plant: compressor vs pump based A B C D A BC DE

15. A.P.Colijn15 NIKHEF CO2 effort Interest from NIKHEF ATLAS group –physicist (Fred Hartjes, Auke-Pieter Colijn, Els Koffeman) –physicist/engineer (Bart Verlaat expertise…) LHCb cooling work finishes in near future We plan to setup CO 2 test-bed at NIKHEF: –for NIKHEF detector R&D (Gossip) –for ATLAS upgrade development: support back-of- envelope calculations of this talk with measurements

16. A.P.Colijn16