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This paper presents results of preliminary investigations of the current decay phase in recent JET major disruptions, where the plasma is bounded by beryllium limiters and a beryllium gettered wall. The average decay time of the current is 175 ms, about 14 times longer than the initial decay time for carbon-bounded disruptions. Vertical stability is often lost before the current has decayed significantly, leading to substantial net vertical forces on the vacuum vessel. Subsequent interaction of the plasma with the top or bottom divertor tiles leads to increased impurity contamination, cooling of the plasma and a second phase of more rapid current decay. Unlike carbon limiter disruptions, no runaway current plateau is observed for carbon-bounded X-point disruptions, although in some cases a small hesitation in the current decay is observed that is coincident with the hard X-ray and photoneutron signals associated with runaway electrons. The total photoneutron yield in X-point disruptions is at least 10 times smaller than that measured from limiter discharges.

Additional information

Authors: HARRIS G R, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-R(90)07 EN (1990) 25 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199110564 / Last updated on: 1994-12-02
Original language: en
Available languages: en
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