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Abstract. The results of experiments on a modulation of halo current through a rail limiter and of x-ray emission from the limiter under the influence of rotating magnetic islands are presented. The external part of the halo-current circuit connected the rail limiter at one side and the discharge chamber with a circular limiter at the other side. A controllable connector that was switched on at a preprogrammed moment of time during the tokamak discharge was introduced into the circuit. In discharges with MHD activity, oscillations of the halo current were observed. The frequency of the oscillations was equal to the frequency of the dominant mode of the poloidal magnetic field perturbation. In some conditions the switching on of the connector in the halo-current circuit resulted in a shift of the MHD mode frequency. This means that the halo current can influence the rotation velocity of the magnetic islands. In the case of low plasma density, repetitive spikes of hard x-ray emission from the rail limiter were observed. These spikes were coherent with the MHD-activity signal and the halo-current oscillations. It can be concluded that besides an effect of magnetic islands resulting in halo-current and x-ray modulation with the frequency of MHD activity, an influence of halo current on the magnetic island behaviour was observed. This influence can be attributed to a coupling between the magnetic islands and the space-resonant component of the halo-current magnetic field.
IAEA 2001
