Some features of the disruption instability in reversed shear TFTR plasmas

The behaviour of MHD perturbations before and during disruptions in TFTR re versed shear plasmas with q(min) approximate to 2 was analysed. In the q(mi n) region, tearing modes, wavelike modes, and mixed tearing plus wavelike m odes are followed by disruption. Sometimes a helical snake (helix) appears at the X point of the q(min) island. The local outward electron energy tran sport near the X point can be explained by the development of 'positive' ma gnetic islands (islands with positive current perturbations). It is propose d that the disruption is initiated when the X point of the magnetic islands coincides in one toroidal position near the torus equator.