current density and its gradient, therefore affecting the stability of the modes driven by it, such as the tearing mode [@FKR]. The reconnection of the magnetic flux caused by the tearing instability leads to the formation of so-called magnetic islands which, if macroscopic, can significantly affect the performance of fusion experimental device, as their particular topology enhances the radial transport and therefore reduces the confinement.

The stability of the tearing mode is conveniently measured by the stability parameter $\Delta'$, a positive value of which corresponds, in the simplest theoretical models, to an unstable mode [@FKR; @Rutherford]. When pressure effects are neglected and the boundary conditions of the problem are fixed, $\Delta'$ is a function of the $m=0$, $n=0$ component of the current density and of the wave vector of the perturbation, $\mathbf{k}$, only.

In Refs.[@Zakharov1989; @Westerhof1990; @Connor1992] it was shown that, even if $\Delta'$ depends on the *global* features of the current density profile, it is strongly affected by the *local* structure of the current density at the resonant surface where $\mathbf{k}\cdot \mathbf{B}=0$. This observation suggested the possibility of controlling the tearing mode by applying small localized current perturbations around the reconnecting surface. In a similar way, however, turbulence generated 