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Abstract

For some time it has not been clear to what extent neutral injected beam ions have a stabilizing influence on sawteeth. To investigate this, the well known toroidal internal kink instability is generalized to account for weakly anisotropic and flowing equilibria. An analytical approach is proposed, which upon employing an appropriate model distribution function, accurately accounts for the hot ion response of neutral beam injection (NBI) to the internal kink mode. Large fluid contributions, which are expected to arise as a consequence of the anisotropic velocity deposition of NBI, are identified and shown to be stabilizing to the internal kink mode for populations with large passing fractions. In particular for tangential injection, such as that employed in the Joint European Torus [J. Wesson, Tokamaks, 2nd ed. (Oxford Science, Oxford, 1997), p. 581], it is found that fast ion stabilization can be dominated by anisotropic fluid effects rather than kinetic effects. In contrast, for predominantly trapped populations, the anisotropic fluid effects are destabilizing and thus reduce the stabilizing role of fast ions. This is especially evident for cases where the subsonic sheared toroidal plasma rotation induced by unbalanced NBI reduces kinetic stabilization. Sheared plasma rotation orientated either co or counter to the plasma current can reduce fast ion stabilization, but counter-rotation has the greatest effect by impeding the conservation of the third adiabatic invariant.

Additional information

Authors: GRAVES J P, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH);SAUTER O, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH);GORELENKOV N N, Princeton Plasma Physics Laboratory, Princeton (US)
Bibliographic Reference: An article published in: Physics of Plasmas, April 2003, Volume 10, Issue 4, pp. 1034-1047
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://dx.doi.org/10.1063/1.1557592
Record Number: 200316319 / Last updated on: 2003-05-30
Category: PUBLICATION
Original language: en
Available languages: en