Shear and minimum B in magnetic configurations with combined helical fields

An asymmetric arrangement of the conductors of a helical stellarator winding and currents passing through them unequal in absolute value cause the formation of a spatial magnetic axis. In the vicinity of this axis the useful volume bounded by a certain surface exhibits the principal properties needed to stabilize a number of plasma instabilities – shear and minimum . This paper is a detailed analytical study of asymmetric systems of this kind. It is demonstrated that the use of the second and third harmonics of a helical magnetic field in devices with a high aspect ratio makes it possible to obtain δV′/V′ between 0.08 and 0.15 for shear S* =0.05 and 0.13 and a useful volume of sufficient size. The configurations considered can be used to create closed magnetic traps for the purpose of confining a high-temperature plasma and studying the stabilizing effect on it of shear and minimum , both together and separately.