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Detector Cooling

Detector Cooling. Jaak Lippmaa HIP, University of Helsinki. State of play OCT 2006. Detectors are in Secondary Vacuum To reduce Conductive and Convection heat load To minimize Detector<>Pocket Wall distance Detectors are in Neutral Gas Atmosphere To avoid vacuum equipment in the tunnel

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Detector Cooling

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  1. Detector Cooling Jaak Lippmaa HIP, University of Helsinki Manchester December 10-12, 2006

  2. State of play OCT 2006 • Detectors are in Secondary Vacuum • To reduce Conductive and Convection heat load • To minimize Detector<>Pocket Wall distance • Detectors are in Neutral Gas Atmosphere • To avoid vacuum equipment in the tunnel • Simpler mechanics Manchester December 10-12, 2006

  3. State of play OCT 2006 • Should we cool the Beam Pipe to reduce Radiative heat transfer from Pocket Wall to Detectors • Should we cool part of Pockets facing Detectors (Stainless Steel is bad heat conductor) • Should we discard Radiative heat load altogether since the effective area of Detectors is small (40 mm2 for 10 planes) Manchester December 10-12, 2006

  4. Pocket PlayCourtesy of Berend Winter Benoit reported reduction of inward bend down to 80 micron, but we still want to study possible bending due to local cooling of the Pocket Wall 300 micro-meter wall thickness (purple) Pressure vectors (Pointing inwards – 100,000 Pa) 3 mm wall thickness (green) Manchester December 10-12, 2006

  5. Pocket PlayCourtesy of Berend Winter This is how mere vacuum deforms the pocket. Even the 100 micron range deformations should be accounted for in the Alignment Procedures Manchester December 10-12, 2006

  6. Pocket PlayCourtesy of Berend Winter -30ºC Cold Spot in the Pocket Wall ΔT=50ºC (ambient temperature is 20ºC) Manchester December 10-12, 2006

  7. Pocket PlayCourtesy of Berend Winter Pressure Pressure and thermal Undeformed reference (deformation is amplified in the graphics) Deformation pulled back due to thermal contraction as much as 30 microns Manchester December 10-12, 2006

  8. Pocket Play • Local cooling introduces inevitable mechanical strain on the Thin Window • Thermal gradients influence total deformation caused by atmospheric pressure on the Pocket • Conclusion:Cooling Pockets partially may not be such a good idea after all!!! Convective Heat Transfer increases “Cool Area” to a section when Detectors are not in Secondary Vacuum Manchester December 10-12, 2006

  9. Pocket Play • Should we cool the Beam Pipe to reduce Radiative heat transfer from Pocket Wall to Detectors – • Probably NOT as it needs loads of cooling power • Should we cool part of Pockets facing Detectors (Stainless Steel is bad heat conductor) – • Probably not as it introduces additional deformations to the Thin Window AND would be mechanically complicated AND increase the “cool mass” anyway Present cooling through Copper Heat Sinks is constrained – certain temperature gradient over the detector area in X direction is unavoidable. WE NEED TO REDUCE CONVECTIVE HEAT TRANSFER !!! Manchester December 10-12, 2006

  10. Heat Loads BOX: L=100 mm W=134 mm H=100 mm H L W I2R Load Convection Conduction Insulation Loss Radiative Transfer Manchester December 10-12, 2006

  11. Heat Loads • I2R Load = assume 25 W • Radiative • Si+Cu ->0.01 mW • Box ->0.002 W • Convective • (N2) 0.4 W • (vacuum) 0 W • Conductive • Only contact is Heat sink • Load Essentially I2R Tamb = 25 °C Tc = -30 °C TDET = -20 °C Copper Heatsink Detector Beam BOX Manchester December 10-12, 2006

  12. Cooling Options • Since the heat load inside the Box is essentially electrical heat generated by the Detector… • Especially when the Detectors are in Secondary Vacuum… • Need to integrate CF cooling with TOTEM and ATLAS • We should consider Thermoelectric Cooling (TEC) Manchester December 10-12, 2006

  13. TEC - Intro • No moving parts • MTBF ≈ 100000 h • No gases involved • Temperature control is easy down to fraction of degree • Tubes not needed • Vacuum compatible devices available Manchester December 10-12, 2006

  14. TEC – Radiation Hardness • Bi-Te and Pb-Te compounds are used in TEC units • Measurements of doped TEC compounds (Seebeck Coefficient and Conductivity) have been carried out in neutron fluxes up to 1.6 x 1019 (fast neutrons) by General Electric Company (Knoll Atomic Power Laboratory) in 1960 • Compounds are radiation tolerant (Bi-Te more so) • Increase in resistivity and SC is due to decrease of carrier concentration • Radiation damage can be annealed at temperatures below 300 °C • Changes can be compensated by adjusting current and voltage • TEC elements are in use in ATLAS laser cooling Manchester December 10-12, 2006

  15. TEC Selection • One TEC could be sufficient • Two (Mounted Top and Bottom) is better due to twice smaller heat load Manchester December 10-12, 2006

  16. SUMMARY • Cooled radiation shield around Tracker (Benoit’s Green Box as proposed by Mimmo) • Vacuum is absolutely necessary if we want GASTOF and Silicon Trackers in the same box • Thermoelectric cooling is an option • Pocket wall stays warm Manchester December 10-12, 2006

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