Performance of the Cold Ejector of the Jet Cryoplant

At JET a cold ejector is used to pump 3 large cryopump systems to a pressure below the suction pressure of the cryoplant compressor (160 gs−1/1.3 b absolute) down to 250 mb below atmospheric pressure. The cold ejector has been successfully operated for over 2 years and had to cope with stringent dynamic conditions such as for cooldown and cryopump regeneration. The performance characteristic of the cold ejector has been analysed by calorimetric measurements with a power of up to 300 W and for flow rates of up to 60 gs−1. The pumping of gas, vapor and liquid have been compared. The results will be presented and operational aspects discussed.