Parametric analysis of magnetic islands subject to halo-current perturbation in disrupting tokamak plasmas

Abstract

Results of simulation and parametric analysis of magnetic island production by helical magnetic perturbation generated under non-axisymmetric halo current are presented. Predictions are made for a cylindrical ITER-size plasma in conditions of disruption. Calculations are carried out with the TEAR code based on the visco-resistive MHD approximation. The radial distribution of the magnetic flux perturbation is calculated with account of the external helical field produced by halo current. The equations for the magnetic flux perturbation describe the dynamics of the tearing mode depending on plasma rotation. In sequence, this rotation is affected by electromagnetic forces depending on the tearing mode magnetic field and external magnetic perturbation. The coupled diffusion-type equations for the helical flux function and for the plasma rotation velocity are numerically treated in a similar way. The magnetic island behavior is analyzed for different plasma parameters expected at the Current Quench stage of disruption. The calculated width of the produced magnetic islands extends to a significant part of plasma minor radius.