Theory of 3D plasma equilibria

A brief review of results of stellarator plasma equilibrium studies based on 2D and 3D codes as well as on analytical approaches is given. The most essential differences between stellarators and tokamaks are described from the viewpoint of equilibrium. A physical interpretation of the non-monotonic behaviour of the rotational transform χ at a rather high plasma pressure in ordinary stellarators with a planar axis is given and the possibilities of correcting the behaviour of χ by a transversal quadrupole magnetic field are considered. The approach to 3D simulation of equilibria in stellarators based on the 'natural' and 'co-natural' coordinate system concept and realized with the POLAR 3D code is described. (author)