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Since July 1990 JET has experienced three occasions where air leaks greater than 1.0 E4 mbar.l/sec happened at a time when the JET vacuum vessel has been under operational conditions at 300 C. Recovery after these incidents to a point at which plasma pulses are successful has involved a bake to high temperature (350 C) followed by a prolonged period of glow discharge cleaning (circa 120 h) to remove the oxygen present as a result of the air ingress and then a beryllium evaporation to getter any remaining impurities. Plasma performance before and after conditioning is compared and an understanding of the mechanism of oxygen removal presented. It is shown that, after an air leak of the magnitude under discussion, vessel conditioning by glow discharge cleaning is essential for the successful resumption of plasma operation and that any future large fusion machines will need such a facility.

Additional information

Authors: ORCHARD J C, JET Joint Undertaking, Abingdon, Oxon. (GB);PEACOCK A T, JET Joint Undertaking, Abingdon, Oxon. (GB);SAIBENE G, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(92)66 EN (1992) 12 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
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