Gas balance in ASDEX Upgrade with tungsten first wall

Gas balance investigations were performed at the strongly pumped divertor tokamak ASDEX Upgrade. The gas inlet and pumping systems have been recalibrated, reaching an accuracy of about 3%, which is mostly given by uncertainties of the gas temperature. Clear saturation of the wall is observed after the wall is loaded with 19 × 10 21 at almost independent from details of the discharge program. For a saturated wall the retention of 1.5 ± 3.2 % is found. In former carbon wall experiments wall saturation is also found, but a higher D-retention is observed.