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Studies of first-wall surfaces from tokamaks have shown that large quantities of hydrogen isotopes are trapped on these surfaces following tokamak operations. This retained gas inventory, or "surface reservoir" is about 100 times greater that the amount of gas required to fuel a plasma, so a small perturbation in the surface composition during a pulse may have serious consequences. Difficulties in establishing discharges following a plasma disruption, or after carbonisation, may be related to changes in the surface reservoirs. This paper demonstrates that about 1.6 x 1.0 E23 atoms of deuterium are released on exposure of the in-vessel surfaces to air. Thus a large part of the "surface reservoir" is readily accessible to the gas phase. There are two obvious corollaries of these results. Firstly, samples removed from a torus for post-mortem analysis (which have inevitably been exposed to air) have already lost this component of the deuterium. Secondly, precautions must be taken before venting the vessel once significant amounts of tritium are present on the walls.

Additional information

Authors: COAD J P, JET Joint Undertaking, Abingdon (GB)
Bibliographic Reference: Report: JET-P(88) 28 EN (1988)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
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