Stellarator, hybrid stellarator, torsatron and low-shear stellarator studies

(I) Equilibrium and stability studies using the stellarator expansion: the stellarator expansion reduces the three-dimensional MHD equations to two-dimensional ones and is applied to a model of Heliotron E. (II) Electron transport studies using the stellarator expansion: the stellarator expansion makes possible an estimate of ''superbanana'' electron heat transport. (III) Toroidal stellarator equilibria: it is shown how the vertical field, which produces no net body force, can shift vacuum flux surfaces and centre an equilibrium. (IV) Ballooning-mode equations for stellarators: ideal MHD ballooning-mode equations are derived for stellarators in the stellarator expansion. (V) Numerical studies of zero-net-current torsatrons: a fully three-dimensional computer code, based on an ideal MHD model, has been used to find stellarator configurations with finite critical values of the plasma parameter #betta#. (VI) Low-shear stellarator studies: configurations whose magnetic axes are three-dimensional curves are studied; low-shear systems are considered for which the equilibrium and stability equations are simple; systems which have applied helical fields such as the Wendelstein stellarator are studied as well as configurations in which the rotational transform arises from geometry such as the figure-eight stellarator (in both cases families of equilibria are found, some of which are shown to be stable). (author)