The design and prototyping of the ATLAS inner detector evaporative cooling system

ATLAS is one of two general purpose LHC experiments, which consists of several sub-detector systems with the inner detector being one. The inner detector consists of the transition radiation tracker, (the TRT), the semiconductor tracker, (the SCT), and the silicon pixel detector. Only the silicon based detectors of the inner detector will be discussed here. The silicon system is based on a modular design with each detector modules dissipating up to 10 W each. The modules are grouped together to give a maximum of 250 W of power on any given cooling stave. Due to radiation damage requirements a maximum silicon temperature of -7°C or lower is required for both systems during operation. This has to be obtained by introducing a minimal amount of extra material into the detector volume. An evaporative cooling system based on C₃F₈ has been devised and extensively tested for this purpose. The system utilizes sub-cooling to minimize the mass flow and thus pressure drops throughout the system. This paper will discuss the overall design, with motivations, present details on specific individual components and demonstrate the performance of the system as a whole.