Studies of the deformable effects on the feedback stabilization of axisymmetric modes in tokamak plasmas
A new linear MHD stability code, NOVA-W, is described and applied to the study of the feedback stabilisation of the axisymmetric mode in deformable tokamak plasmas. The NOVA-W code is a modification of the non-variational MHD stability code NOVA which includes the effects of resistive passive conductors and active feedback circuits. The vacuum calculation has been reformulated in terms of the perturbed poloidal flux, to allow the inclusion of perturbed toroidal currents in the region surrounding the plasma. The boundary condition at the plasma-vacuum interface relates the instability displacement to the perturbed poloidal flux. The NOVA-W code is used to examine the effects of plasma deformability on feedback stabilisation. It is seen that plasmas with strongly shaped cross sections have an unstable motion different from a rigid shift. Furthermore, the placement of passive conductors is shown to modify the non-rigid components of the motion in a way that reduces the stabilising effects of these conductors. The eigenfunction is also modified under the effects of active feedback. This deformation is seen to depend strongly on the position of the flux loops. The variations of these non-rigid components of the eigenfunction always serve to reduce the stabilising effect of the active feedback system, by reducing the measurable poloidal flux at the flux-loop locations. The code is applied to the highly elongated TCV design equilibrium. Also presented are results of calculations using the CIT design equilibrium and the PBX-M configuration.
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: 199110429 / Last updated on: 1994-12-02
Original language: en
Available languages: en