Ultra-simple stellarators

An ultra-simple approach to achieving a high rotational transform, low aspect ratio toroidal magnetic confinement system is presented, featuring just two planar coils, optionally interlinked. The effect of the principal free parameters on the vacuum magnetic topology of the configuration is explored, suggesting a compromise between minimizing magnetic field ripple and plasma aspect ratio. It appears that an attractively simple, magnetically robust design can be achieved, with the possibility of further improvements by more sophisticated optimization of the coil shapes. (author)