The Semiconductor Tracker (SCT) of the ATLAS Inner Detector must be operated at a constant temperature of -7 C. The cooling system must be capable of removing about 24 kW of heat. To accomplish this, a novel system has been developed at the Rutherford Appleton Laboratory which uses "Binary-Ice«" cooling.
|"Binary-Ice " is a suspension
of ice crystals of sizes ranging from 50Ám to 500Ám in
an aqueous medium containing a freezing point depressant.
In the current design, a mixture of 80% water / 20%
methanol is used.
Almost all of the heat applied to a bath of Binary-Ice fluid is absorbed by the latent heat of melting and thus results in near isothermal behaviour, in contrast to conventional cooling systems which operate with a substantial temperature gradient between inlet and outlet. This is illustrated in the graph which shows the increase in temperature relative to the inlet temperature for liquid and Binary-Ice coolants.The fluid flows along a 3 mm diameter pipe which is uniformly heated. The flow rate is about 5.5 ml/s and the total heat load is 48.5 W. In each case, the alcohol / water mixture is identical.
The Binary-Ice fluid is produced in commercially available generators, supplied by Integral Technologie GmbH. For the last two years, a 1.7kW machine has been operated at RAL. For ATLAS, the pipework inside the Inner Detector will be operated as a "Leakless Cooling System«", based on a design developed at CERN.
To prepare for the design of the final ATLAS system, a team of scientists and engineers from RAL and the University of Oslo are studying the kinematic properties of these fluids, developing flow and ice concentration monitors and writing slow control and data acquisition software.
Binary-Ice is a registered trade mark of Integral Technologie GmbH, Flensburg, Germany