(TH/P3-8) Feedback Stabilization of Resistive Wall Modes in the Presence of Multiply-connected Wall Structures

Abstract.  The feedback stabilization of resistive wall modes (RWM) for realistic wall structures has been studied splitting the problem in two parts. In the open-loop part the complete set of eigenvalues and eigenfunctions of the plasma-resistive wall system without feedback currents has been determined. Then, in the closed-loop part an initial value problem has been formulated for the time evolution of the RWM and the currents of the feedback coils. The interaction of the feedback currents and of the RWM's are given by prescribing the feedback logic. The effectiveness of the feedback can be studied by solving the characteristic equation of the closed-loop system. The procedure has been implemented numerically: STARWALL code. The equilibrium data are provided by the VMEC code, the potential energy of the plasma perturbation is provided by the CAS3D stability code. The magnetic field in the vacuum region with the resistive wall has been calculated with a finite element procedure, an appropriate method for treating cases with multiply-connected wall configurations. It is assumed that the resistive wall modes are slow so that the kinetic energy of the plasma perturbation can be neglected. Applications for ASDEX Upgrade are presented.

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