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During the beryllium phase of JET, hydrogen (H(2), HD, D(2)), hydrocarbon (C(x)H(y)) and CO outgassing after discharges has been analysed by means of mass spectroscopy and Penning gauges. The analysis has been performed over a period of up to 3000 seconds after ohmic and additionally heated limiter and X-point discharges. It has been found that the temporal behaviour of hydrogenic outgassing can be characterised by a uniform power law t(-n) with n = 0.73 +/- 0.1 which is independent of plasma operation parameters. This result is discussed in view of possible transport and retention mechanisms in, and deuterium release mechanisms from, plasma facing surfaces. It is concluded that several mechanisms can explain the release behaviour. However, one of the most plausible explanations is accumulation of hydrogen in limiters and walls. Outgassing of hydrocarbon and CO were significantly lower under beryllium wall conditions as compared to the earlier all carbon wall conditions.

Additional information

Authors: PHILIPPS V, JET Joint Undertaking, Abingdon, Oxon. (GB);EHRENBERG J, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(92)41 EN (1992) 26 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199211288 / Last updated on: 1994-11-29
Original language: en
Available languages: en