This kind of prototype generator has a simple construction, and is often referred to as a Torus machine. It is a slotless, double-sided, axial flux, permanent magnet, disc-typed machine. The two rotor discs are made of mild steel and have surface-mounted permanent magnets to produce an axially-directed magnetic field in the machine air-gaps. The machine stator comprises a slotless toroidally-wound strip-iron core which carries a three-phase winding in a toroidal fashion by means of concentrated coils. The coils have rectangular shape according to the core cross section. The axially-directed end-winding lengths are relatively short, yielding low resistance and reduced power loss. The active conductor lengths are the two radial portions facing the magnets, the polarities of which are arranged to induce additive EMFs around a stator coil