Initial conditioning of the TFTR vacuum vessel

We report on the initial conditioning of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel prior to the initiation of first plasma discharges, and during subsequent operation with high power Ohmically heated plasmas. Following evacuation of the 86‐m3 vessel with the 104 1/s high vacuum pumping system, the vessel was conditioned by a 15‐A dc glow discharge in H2 at a pressure of 5 mTorr. Rapid‐pulse discharge cleaning was used subsequently to preferentially condition the graphite plasma limiters. The effectiveness of the discharge cleaning was monitored by measuring the exhaust rates of the primary discharge products (CO/C2H4, CH4, and H2O). After 175 h of glow discharge treatment, the equivalent of 50 monolayers of C and O was removed from the vessel, and the partial pressures of impurity gases were reduced to the range of 10−9–10−10 Torr.