The internal kink mode in an anistropic flowing plasma with application to modelling neutral beam injected sawtoothing discharges
For some time it has not been clear to what extent neutral injected beam ions have a stabilising effect on sawteeth. To investigate this, the well known toroidal internal kink instability is generalised to account for weakly anistropic 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 anistropic velocity deposition of NBI, are identified and shown to be stabilising 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, it is found that fast ion stabilisation can be dominated by anistropic fluid effects rather than kinetic effects. In contrast, for predominantly trapped populations, the anistropic fluid effects are destabilising and thus reduce the stabilising role of fast ions. This is especially evident for case where the sub-sonic sheared toroidal plasma rotation induced by unbalanced NBI reduces kinetic stabilisation. Sheared plasma rotation orientated either co or counter to the plasma current can reduce fast ion stabilisation, but counter-rotation has the greatest effect by impeding the conservation of the third adiabatic invariant.
Bibliographic Reference: EPFL Internal report LRP 745/02, January 2003. 35pp.
Availability: Available free of charge from: École Polytechnique Fédérale de Lausanne (EPFL), Ecublens, CH-1015 Lausanne Fax +41-21-6934747
ISBN: ISSN: 0458-5895
Record Number: 200315920 / Last updated on: 2003-02-19
Original language: en
Available languages: en