Effect of a ferromagnetic wall on low β tearing modes in the Japan Atomic Energy Research Institute Fusion Torus-2 Modified

A ferritic steel wall, which might be employed in fusion demonstration reactors, has been installed in Japan Atomic Energy Research Institute Fusion Torus-2 Modified [Nucl. Fusion 41, 257 (2001)] to study the applicability of ferromagnetic walls to plasmas. The tearing mode equation is solved in presence of a ferromagnetic/resistive wall to study the effect of the ferromagnetism on the tearing mode stability in tokamaks. It is shown that a ferromagnetic wall has a weak effect on the surface tearing modes depending on the current profile. The destabilization effect due to the attraction of the perturbed magnetic field by permeability is shown to be very small compared to the stabilization effect of the conducting wall.