Abstract
The MHD activity of plasma configurations with reversed magnetic shear has been investigated on the FTU tokamak. In the presence of pairs of surfaces with the same rational value q = m/n of the safety factor, double-tearing modes are excited which give rise in most cases to bursts of sawtooth-like profile rearrangements. More stable regimes have also been found, in which the activity is dominated by rotating saturated modes. In a particular case with 
and 
a discharge without any detectable MHD activity during the current flat-top has been obtained. In high-temperature regimes (
at 
), an irregular activity has been detected near the plasma centre which could be due to the excitation of resistive interchange modes.
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