Two-dimensional model of conventional stellarator

MHD theory of conventional stellarators is founded on the basis of so-called stellarator expansion. The expansion is introduced from the beginning. Four or the more expansion parameters are assumed to be small. This makes the derivation rather complicated and all expressions approximate. Furthermore the restoring of the exact known results can not be recovered. The above shortcomings lead to the mistrust of two-dimensional models of stellarators. This is not true, but the 2D models are always quite reliable indeed. The basic equation is direct consequence of Maxwell's equations, and nothing artificial. (M. Tanaka)