Development of Fluorocarbon Evaporative Cooling Recirculators and Controls for the ATLAS Pixel and Semiconductor Tracking Detectors

We report on the development of evaporative fluorocarbon cooling recirculators and their control systems for the ATLAS Pixel and Semiconductor Tracking (SCT) detectors. A prototype circulator uses a dry, hermetic compressor with C3F8 refrigerant. The mass flow rate and operating pressure in each circuit is individually tuned via feedback according to the circuit load variation, using analog air pressure-piloted regulators. A hard-wired thermal interlock system automatically cuts power to individual silicon modules should their temperature exceed safe values. All elements of the circulator and control system have been implemented in prototype form. Temperature, pressure and flow measurement and control use 150+ channels of standard ATLAS LMB ("Local Monitor Board”) DAQ and DACs on a multi-drop CAN network administered through a BridgeVIEW user interface. Prototype 16 channel interlock modules have been tested. Highly satisfactory performance of the circulator under steady state, partial-load and transient conditions were seen with proportional fluid flow tuned to varying circuit power. Future developments are outlined.