anymore.

To complement this analysis, we have independently calculated with a different numerical code the value of $\delta\Delta'$ associated to the corrugations and the equilibrium described above. The code, that is also used to obtain the cylindrical results presented in the next Section, can solve Eq.\[4\] or its slab version by using a “shooting” algorithm. As Fig.\[fig4\] shows, the numerical values of $\delta\Delta'$ perfectly match the cubic behavior predicted by the scaling in Eq.\[9\], thus confirming its validity.

We complete this study by showing that a current corrugation with the appropriate phase can drive a linear tearing mode even when the “smooth” equilibrium would assure stability. In Fig.\[fig5\] we describe three cases, with $\Delta'_0=0$ (red squares), $\Delta'_0=-0.29$ (blue circles) and $\Delta'_0=-0.8$ (green crosses), for a corrugation of amplitude $A=1\times 10^{-4}$.

As expected, if the wavelength of the corrugation exceeds a critical threshold, depending on $\Delta_0'$, the instability can be excited. We conclude remarking that, for $\alpha=0$, the choice of a positive $A$ leads to destabilization, while a negative value would produce the opposite effect.

Effect in cylindrical geometry
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The analytic results in Section III suggest the possibility that the stability of the tearing mode can be significantly affected by 