Free boundary toroidal stability of ideal and resistive internal kinks
The ideal and resistive stability of internal kink modes in tokamaks is studied numerically using the full MHD equations. For ideal modes, stability limits in beta(pol) are shown for sample q-profiles as functions of plasma shape, q = 1 radius and wall position. Shaping is found to have a rather strong effect, with ellipticity destabilising and triangularity stabilising. When the q = 1 radius is large, the wall position significantly influences the stability of the internal kink, and for large ellipticity, even equilibria with beta(pol) = 0 can be unstable when the wall is at infinity. These code results are compared with large aspect ratio theory. Cases relevant to ITER design are presented. A previous study indicated that the resistive internal kink mode can be stable for equilibria with low shear at the q = 1 surface. It is found that while equilibria with q(0) less than 1 can be resistive-MHD stable in the presence of a close fitting wall, they are generally unstable when the wall is at infinity. For practically all cases, the free boundary resistive MHD instabilities are enhanced by pressure, as the average curvature tends to be unfavourable at the q = 1 surface, in particular at large ellipticity. Physical mechanisms that may reduce the curvature effects are discussed.
Bibliographic Reference: Paper presented: 18th European Conference on Controlled Fusion and Plasma Physics, Berlin (DE), June 3-7, 1991
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Record Number: 199110439 / Last updated on: 1994-12-02
Original language: en
Available languages: en