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Abstract

The very peaked pressure profiles in some pellet-fuelled discharges with ion cyclotron resonance heating (ICRH) in the Joint European Torus (JET) are terminated by an abrupt flattening of the temperature profile. This appears to be the result of an instability with a very fast time-scale which is triggered when the safety factor q drops below 1.5. The ideal m/n = 3/2 infernal mode, which is excited only when q is very close to 1.5, may well be the instability responsible. Linear magnetohydrodynamic (MHD) stability calculations, based on equilibria that model the relevant JET discharges as closely as possible, yield growth rates consistent with the rise time of the instability. Nonlinear calculations initialised with the same equilibria exhibit plasma behaviour very similar to that seen experimentally: a flattening of the pressure profile occurs, a residual m=3 structure is present after the flattening, and the time scale for the flattening is in reasonable agreement with experimental observations. It is thus concluded that the ideal infernal mode is an excellent candidate for the instability.

Additional information

Authors: CHARLTON L A ET AL., Oak Ridge National Laboratory, Oak Ridge (US);EDWARDS A, JET Joint Undertaking, Abingdon, Oxon. (GB);KUPSCHUS P, JET Joint Undertaking, Abingdon, Oxon. (GB);O'ROURKE J, JET Joint Undertaking, Abingdon, Oxon. (GB);HAMMETT G W, Princeton Plasma Physics Laboratory, Princeton, New Jersey (US);SCHMIDT G L, Princeton Plasma Physics Laboratory, Princeton, New Jersey (US)
Bibliographic Reference: Report: JET-P(90)65 EN (1990) 17 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199110885 / Last updated on: 1994-12-02
Category: PUBLICATION
Original language: en
Available languages: en