Peaking factor and external field dependence of n = 1 RWM forces on tokamak wall

Abstract

This paper finalizes the self-consistent study of the sideways force acting on the resistive wall due to eddy currents induced by n = 1 kink instability under variations of the external poloidal field and its impact on the force peaking factor as outlined in A. A. Martynov and S. Yu. Medvedev, Phys. Plasmas 27, 012508 (2020). A proper analytical treatment of the sideways forces for a large aspect ratio circular tokamak is limited to the case q < 1 with a dominating m/n = 1/1 mode and only weak coupling to sideband poloidal harmonics, which asymptotically does not contribute to the force. The present paper shows that in the 1D case, the net sideways force does not depend on variations of the external equilibrium poloidal field with a difference in the force peaking factor only: the corresponding analytic expressions have been derived. For realistic 2D cases, the behavior of both the net force and the peaking factor changes due to mode coupling and does depend on the variations of the equilibrium magnetic field at the wall. In particular, for q > 1 at the plasma boundary, the sideways force is generated by a sideband m/n = 1/1 harmonic, which gives lower net force as compared to the q < 1 case, but with a higher peaking. The numerically estimated magnitude of the sideways force density was found to be insignificant for ITER that calls for taking into account the plasma−wall contact in disruption modeling.