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Abstract

It is shown that pressure-driven, ideal external modes in tokamaks can be fully stabilised by resistive walls when the plasma rotates at some fraction of the sound speed. For the modes rotating with the plasma, the stabilising effect of the wall increases when the wall is brought closer to the plasma, while, for the wall-locked modes, the stabilisation improves with increasing wall distance. When the plasma rotates at some fraction of the sound speed, there is a window of stability to both the wall-locked and the rotating mode. This window closes when beta exceeds a new limit which can be significantly higher than the wall-at-infinity limit. The stabilisation depends principally on the toroidal coupling to sound waves and is affected by ion Landau damping. Two dimensional stability calculations are presented to evaluate the gains in beta limit resulting from this wall stabilisation for different equilibria and rotation speeds. In particular, results are shown for advanced tokamak configurations with bootstrap fractions of approximately 100 %.

Additional information

Authors: WARD D J, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne (CH);BONDESON A, Uppsala University, Euratom-NFR Association, Department of Technology (SE)
Bibliographic Reference: Report: LRP 502/94 EN (1994) 18 pp.
Availability: Available from Confédération Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, 21 avenue des Bains, 1007 Lausanne (CH)
Record Number: 199411472 / Last updated on: 1994-12-06
Category: PUBLICATION
Original language: en
Available languages: en