Destabilization of nonlinear resistive wall mode due to suppression of poloidal rotation in a cylindrical tokamak

Abstract

It is known that linear resistive wall modes (RWMs) can be stabilized by a poloidal rigid rotation. Nonlinear behavior of unstable RWMs has been studied in a cylindrical tokamak plasma with such a poloidal rotation. When a resistive wall is very close to the plasma surface (rw/a≃1.2) significant reduction of the poloidal rotation due to the Maxwell stress occurs in the neighborhood of resonant surface of (m,n)=(2,1), where m (n) is a poloidal (toroidal) mode number. Thus the nonlinear saturated state does not depend on the magnitude of poloidal rotation. However, when the resistive wall position is close to the ideal wall stabilization limit (rw/a=1.3) or rw/a≃1.27, the poloidal rotation remains in the nonlinear phase for a large poloidal rotation case. In this case, nonlinear saturation with a small amplitude level becomes possible. The role of Maxwell stress is clarified by introducing magnetic island width and rotational torque for the reduction of poloidal rotation.