device invented by Lyman Spitzer for the containment of a plasma inside a racetrack-shaped (sometimes a figure-8) tube. The plasma is contained by a magnetic field created by helical windings around the tube. More generally, a toroidal sort of device that attempts to average out particle drifts that would otherwise take plasma to the walls of the vacuum vessel by imposing a given amount of helicity to the toroidal field lines. A toroidal plasma configuration, which, unlike a tokamak, is not axially symmetric. The poloidal fields necessary for confinement are produced by external coils (rather than a current in the plasma), either helical coils in addition to plane toroidal field coils, or out-of-plane toroidal field coils (pioneered in Germany on Wendelstein 7-AS). The stellarator is generally considered to be the most serious alternative to the tokamak. Since the concept is inherently steady state, it would not have the tokamak's problems with thermal and mechanical cycling, current drive, and disruptions.