The structure of the magnetic surfaces in the axial region of an l=3 field

Using analytical methods, the authors investigate the axial region of the magnetic configurations of l=3 traps (stellarator and torsatron) when a uniform transverse field is present. They determine the conditions necessary for the existence of a rosette-type structure of the magnetic surfaces in the axial region as a function of various magnetic trap parameters such as toroidality, the angle of inclination of the helical conductors and the strength of the transverse field. Expressions are found for the critical transverse magnetic field value at which the rosette-type structure disappears. (author)