Force-free coil principle applied to helical winding

The concept of the force-free coil is well known in the field of ultra high field technology. The fact that tokamak plasma, in which large current flows, is capable of maintaining balance in a vacuum by a magnetic field is a logical extension of this concept. In this report, a toroidal field coil and a poloidal field coil are considered more simply as a hybrid coil, and the authors propose a helical torus field coil that can be made capable of greatly reducing the electromagnetic force in the major radius direction by adjusting the winding pitch. A code that optimizes electromagnetic force distribution by disassembling the current density in both directions was developed. The feasibility of this idea was confirmed through experiment