DISRUPTION CONTROL BY THE HELICAL MAGNETIC-FIELD

The growth of m/n=2/1 tearing mode is studied numerically in a new kin d of equilibrium magnetic configuration: a zeroth-order axisymmetric e quilibrium field superposed with a small m/n=7/4 static helical field, where m and n are respectively the poloidal and toroidal mode numbers . The amplitude of the magnetic flux perturbation \psi(2/1)\ is found to be reduced as the magnitude of the m/n=7/4 helical field increases. \psi(2/1)\ can be reduced to zero when the m/n=7/4 magnetic island is large enough that it overlaps the q=2 flux surface. Oscillatory \psi( 2/1)\ is also excited with appropriate the magnitude of the m/n=7/4 he lical field. These results are of practical interest for tokamak react or design.