To investigate how torsion of a magnetic axis influences the equilibrium of high beta plasmas the authors have built a figure-eight stellarator consisting of four half tori. The connection angles of the half tori can be altered, so that the angle of the rotational transform of the magnetic field lines can be changed from 0 degrees to 160 degrees . If the angle of the rotational transform is small, the plasma column, produced by a theta pinch, drifts away and finally is reflected at the tube wall. In contrast, for a larger angle of the rotational transform there are indications that an equilibrium state may be obtained after a certain degree of radial drift. This difference may be qualitatively explained by the fact that magnetic surfaces exist only in the latter case.
N. Takeuchi, I Ono, K Sugita
Plasma Physics and Controlled Fusion