Effects of local features of the equilibrium current density profile on linear tearing modes

It is shown that local features of the equilibrium current density profile, i.e., its gradient and curvature evaluated at the resonant magnetic surface, can modify considerably the linear behavior of tearing modes. These features can become particularly important in cylindrical geometry, at moderate values of the electrical resistivity and of the tearing stability parameter, Δ'. A new analytic dispersion relation is derived, which takes into account in a consistent way these new terms and which agrees very well with numerically computed growth rates.