The SlowControl System for the TRD Gas Circuit of the Alpha Magnetic Spectrometer

The AMS-02 detector was installed on May 2011 on the International Space Station and has since collected billions of cosmic ray events.The Transition Radiation Detector (TRD) of AMS-02 is a key element to identify positrons in Cosmic Rays with respect to the much more abundant protons. The transition radiation generated by charged particles going through a fleece of propylene radiator is captured by modules of straw tubes interleaved with the fleece layers. The straw tubes are filled with a Xe/CO2 mixture. Due to gas diffusion, such mixture has to be refilled periodically in space during the entire life cycle of AMS.The TRD is equipped with a GasCircuit, containing vessels for Xe and CO2 storage, and all the actuators and sensors needed for the composition of the mixture and to refill the TRD straw tubes. This paper describes the architecture of the (GasCircuitSlowControlsystem (the UGC  ) that is used to monitor and control the GasCircuit, the qualification procedure for use in space, and the performance of the system after one year of operation on the International Space Station.