A method for making free a multi-layer toroidal field coil from bending moment is studied by appling File's theory to each winding layer. The theory seems to be valid for a line conductor in a toroidal magnetic field or for an ideal one-layer toroidal field coil. According to the present method, the shape of the multi-layer toroidal field coil is satisfactorily decided so that each winding layer is in pure tension or is not subject to any bending moment. The winding thickness of the resultant coil does not become uniform along the winding. The successive layers are no longer in contact leaving some empty space, and the tension on a conductor varies in magnitude from layer to layer. A practical toroidal field coil with a total ampère-turn of 18.8 MAT, a vertical bore of 1.51m, and a horizontal bore of 1.07m has deen designed by this method.
