On the impossibility of determining tearing mode stability
The effect of local pressure gradients and of a local flattening of the pressure profile around the resonant surface of a tearing mode is investigated in toroidal geometry. It is shown that the stability index calculated from the ideal outer region is modified by local profile changes in a way reminiscent of the favourable curvature stabilisation of linear and non-linear tearing mode layer theory. If the width of the region of pressure flattening is of the order of the linear resistive layer width, the stabilisation from the ideal outer region compensates for the loss of pressure gradient stabilisation from the layer, and the overall stability of the mode is largely unaffected. For pressure flattening over a larger region, however, the mode can be strongly destabilised. Since the flattening region may still be too small to resolve experimentally, this result implies the essential impossibility of determining the tearing mode stability of experimental profiles.
Bibliographic Reference: Report: AEA FUS 70 EN (1990) 10 pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon. OX14 3DB (GB)
Record Number: 199110105 / Last updated on: 1994-12-02
Original language: en
Available languages: en