Operational behaviour of the ASDEX upgrade in-vessel cryo pump

The set-up of the Helium (He) supply circuit for the ASDEX Upgrade cryo pump (CP) with 100 m3/s Deuterium pumping speed is described together with the key instrumentation and the method of data interpretation. The main peculiarities of the CP operation are the hydraulic instability of the mass flow below 4 g/s, due to large level differences of the transfer line and the sudden heat input of 130 W to the cryo panel during He discharge cleaning of the vacuum vessel. In both cases, a maintenance free, immersed Helium Circulating Pump (HCP), simplifies operation considerably. It permits quick re-filling and re-cooling after He-glowing and stabilisation of the standby mass flow in an oscillatory way down to 2.5 g/s. The measured He losses show that continuous operation of the CP, including He-glowing, is feasible even with a standard 30/60 l/h He-liquifier.