Fluorocarbon Evaporative Cooling Developments For The Atlas Pixel And Semiconductor Tracking Detectors

We report on the development of evaporative fluorocarbon cooling for the ATLAS Pixel and Semi-Conductor Tracker (SCT) detectors. Data are presented from cooling studies on representative prototype Pixel and SCT detector thermo-structures, using perfluoro-n-propane (C3F8), -butane (C4F10), trifluoro-iodo-methane (CF3I) and custom C3F8/C4F10 mixtures. Thermophysical properties were calculated for custom mixtures.For most of the structures tested at full projected power dissipation, operation of silicon detector substrates at temperatures below -7 degrees C (required for 10 year lifetime in the radiation environment of LHC) should be possible, albeit in some cases with increases in inner diameter (I.D.) of the coolant tubes from those of the present series of prototypes.Heat transfer coefficients in the range 2-5.10(3) Wm(-2)K(-1) have been measured in a 3.6 mm I.D, heated tube dissipating 100 Watts - close to the full equivalent power (similar to 110 W) of a barrel SCT detector "stave" - over a range of power dissipations and mass flows in the above fluids.Aspects of full-scale evaporative cooling circulator design for the ATLAS experiment are discussed, together with plans for future development.