“Ultimate” Configurations of the L = 1, m = 13 Torsatron and the “VINT-20” Torsatron as a Possibility of Creating a Tandem Stellarator–Mirror Trap Hybrid System

The paper is concerned with numerical investigation of various magnetic configurations of a single-pole toroidal L = 1, m = 13 “ultimate” torsatron having a low aspect ratio A h = 4.345 and the modulation factors (−0.23) ≤ α ≤ 0.71 (K = 1, β = 0) of the helix law −mφ = θ−αKSinθ−βKSin2θ. The extremums of the basic properties of closed magnetic surfaces as functions of the coefficient α in the neighborhood of α ≈ 0.4, as well as the structures of the edge magnetic field (substructures of virtual current) and the separatrix have been first determined for the L = 1, m = 13 “ultimate” torsatrons and the “Vint-20” torsatron. Unusual positions of the separatrix X-points in the cross sections for 1/4- and 3/4- magnetic field periods have been identified. The formula that takes into account the modulation factor α of the helix law was first derived to determine the average vertical magnetic field on the geometrical axis of the torus.