The electromagnetic system for the active control of the non-axisymmetric helical deformation in RFX

Experiments on resistive tearing mode control in a reversed field pinch by applying a rotating magnetic field are presented. After a brief survey of tearing mode characteristics, the actions taken to prevent their detrimental effects are described. These actions consist in the generation of a rotating magnetic field able to modify the dynamic of the m = 0, n = 1 tearing mode. The rotating field is generated by superimposing an alternating current component to the current circulating in the toroidal field winding. To achieve this, the toroidal field circuit was appropriately modified. Under some conditions, the rotating field exerts a dragging torque on the helical deformation of the plasma column, produced by phase-locked m = 1 modes, so that the deformation can be either localized in a selected toroidal position or put into a continuous toroidal rotation.