Effect of Local Driving Helical Current on Tearing Mode Instability

The m=2/n=1 tearing mode instability with local driving helical current was studied by using the reduced magnetohydrodynamics (RMHD) simulation method in the large-aspect-ratio Tokamak. The effects of different characteristics of driving helical current, such as intensity, radial deposition width and starting deposition time were analyzed. The results indicate that the driving helical current with larger intensity and more focused deposition width has a better suppression effect on the tearing modes. But destabilizing effect, called “flip” instability, is also observed when the driving helical current over a certain intensity or with too narrow deposition width. Further more, with the delay of starting deposition time of driven current, it will weak the control effect of driven current on magnetic islands.