Properties of plasma equilibrium in closed hybrid stellarators

For the case of stellerators with nonpolar magnetic axes and average magnetic surfaces having circular cross sections, the following question is studied: Is it useful, from the point of view of plasma equilibrium, to have large values of the rotational transform 1/2π > 1? In contrast to conventional stellarators with a circular magnetic axis, where the maximum equilibrium pressure increases proportionally to (1/2π), in more complicated stellerators consisting of pieces of different shape, i.e., in a figure-eight stellarator, Drakon, or open-quotes piecewise-symmetricclose quotes stellerator, it is shown that as the rotational transform per period approaches a whole number the equilibrium is lost. Furthermore, when 1/2π approaches an integer value and secondary short-circuit currents begin to appear in one of the periods of the system, the maximum equilibrium pressure can become larger than in a conventional stellarator with the same system length and rotational transform. 13 refs., 8 figs