  The generation of zonal magnetic fields in laboratory fusion plasmas is
predicted by theoretical and numerical models and was recently observed
experimentally. It is shown that the modification of the current density
gradient associated with such corrugations can significantly affect the
stability of the tearing mode. A simple scaling law is derived that predicts
the impact of small stationary current corrugations on the stability parameter
$\Delta'$. The described destabilization mechanism can provide an explanation
for the trigger of the Neoclassical Tearing Mode (NTM) in plasmas without
significant MHD activity.
