NIKHEF, ATLAS, CERN
The proposed increased collision rate of the LHC for 2022 requires the installation of a new Inner Detector. Regarding the Silicon Strip Detector, the increased integrated luminosity (from 300 to 3000 fb-1) will increase the radiation damage a factor 10 . Detector support systems should be thinner and lighter to decrease the effect of increased radiation. To avoid the leakage current of silicon sensors increasing and leading to high operating temperatures for the silicon and even worse to reach a situation known as thermal runaway, evaporative CO2 cooling will be used combined with a new cooling scheme with integrated support and cooling functions of the petal.
CO2 evaporative cooling is favourable among others because of its low triple point at high pressure, the high heat transfer coefficient and the small pressure drop for two-phase flow and therefore low temperature gradient along the sensors .Little work has been done regarding the CO2 cooling and support design for the future Silicon Strip Detector for the upgrade phase II. Since there is no industrial experience in such cooling system, models need to be made in order to improve the design and should be based on prototypes. Moreover, the CO2 flow documentation is still limited as well as the heat transfer parameters especially for two-phase CO2 systems in small diameter tubes.
This research project aims to optimize the cooling design of the ATLAS Silicon Strip Detector focussing on the petal, basic component of the Endcap part of the Detector. The thermal performance of a prototype petal will be measured. A thermal FEA model of the prototype will be developed later to give sufficient agreement to the measurements. This verified model will be used to optimize the design of the petal, and to predict reliably the effects of future designs. In parallel with this, there will be study of new materials that can be used for to keep radiation length at minimum and reduce the thermal resistance between silicon and coolant. Also, the flow properties of liquid/vapour mixture CO2 will be studied as well.
J.Bernabeu, Silicon Strip Detectors for the ATLAS HL-LHC Upgrade, 10th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, Florence, Italy, 6-8 July 2011
 G.Hemink, CO2 cooling studies for the ATLAS upgrade, July 2010 https://espace.cern.ch/CO2/Public%20Documents/Presentations%20and%20publications/SLAC/1007_HG_ThesisCO2CoolingStudiesForTheATLASUpgrade.pdf cited: 26/03/2013