Slow control for the TRD gas supply system of AMS-02

AMS (Alpha Magnetic Spectrometer) [http://ams.cern.ch/AMS] is a high energy physics experiment that will operate for three years on the International Space Station. Supersymmetric dark matter could produce an excess in the 10-300GeV positron spectrum. A 10-5 separation of positrons from protons is needed for this signal and will be achieved partially by a TRD (Transition Radiation Detector). Apart from the radiator, the TRD is a gaseous detector is filled with Xe:CO2=80:20 and refreshed by 7 liters of gas per day. This paper describes the TRD gas supply system and the slow electronics control system for it, which will keep gas gain variations below 3%