The resistive wall mode (RWM) dispersion relation is analytically derived for a cylindrical plasma surrounded by two walls: the first wall (facing the plasma) is assumed thin (geometrically and magnetically) and resistive, while the second wall of larger radius is ferromagnetic, but non-conductive. The predictions of this simplified model are verified on the JET tokamak by a comparison with the calculations of a linearized axisymmetric plasma response model. In this case, it is found that, assuming all active and passive conducting structures as short circuited, the presence of iron causes a constant increase in the n = 0 RWM growth rate of around 25 s−1, independently of the plasma configuration under study.
Stability of the resistive wall mode in JET