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We report on the ideal magnetohydrodynamic (MHD) stability of Tokamak field profiles that have a non-monotonic safety factor q(r). An analytic criterion is obtained for these 'inverse shear' profiles by expanding in inverse aspect ratio and assuming that the minimum in q is slightly less than the m/n value of the mode under examination (m and n being the principle poloidal and toroidal mode numbers of the instability). Three terms are identified as controlling the stability of this 'double kink'; 2 of them are stabilising and due respectively to field line bending and the interaction of average favourable curvature with the pressure gradient. The possibility of instability comes from the third term which is due to toroidal coupling and is ballooning in character. The analytical results are compared with those from a fully torodial stability code.

Additional information

Authors: GIMBLETT C G, UKAEA Government Division, Abingdon, Oxon. (GB);HASTIE R J, UKAEA Government Division, Abingdon, Oxon. (GB);HENDER T C, UKAEA Government Division, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: UKAEA FUS 322 (1995) 16pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon, OX14 3DB (GB)
Record Number: 199610337 / Last updated on: 1996-03-29
Original language: en
Available languages: en