of the $n/m$ term in the definition of $\psi_{eq0}'$ that, in cylindrical geometry, appears in the integral of Eq.\[8\].

NTM triggering mechanism
========================

In this Section, we analyze how the zonal fields affect the onset of the Neoclassical Tearing Modes. In order to do that, we employ a reduced version of the generalized Rutherford equation [@Rutherford; @LeHaye2006; @Itoh2004]: $$\label{13} \tau_\eta\frac{dw}{dt}\propto
\Delta_0'+\delta\Delta'+C_0\left(\frac{w}{w^2+w_{boot}^2}-\frac{ww_{pol}^2}{w^4+w_{pol}^4}\right),$$ Consistently with Section III, the island width and the stability parameter are normalized to a macroscopic length scale (e.g. the resonant radius). For sake of simplicity, we retain in the model only the fundamental terms responsible for the stabilization/destabilization of the NTM. In particular, we neglect the current shape term, that strongly affects the island saturation but has little effect on the seed island problem [@Militello2004; @Escande2004] and the stabilizing toroidal curvature effects [@Glasser1975]. Furthermore, we do not take into account the rotation of the magnetic island in a self-consistent manner [@CWW; @Militello2008]. Indeed, in Eq.\[13\] neither the bootstrap term (third on the RHS), nor the polarization term (fourth on the RHS) are explicit functions of the island rotation. The coefficient $w_{boot}$, is a measure of the reduction of the drive associated with the perpendicular transport [@Fitzpatrick1995], $w_{pol}$ is 