Controllable homopolar motor-generator energy storage for application in a fusion power reactor

A scheme for a homopolar motor generator (HMG) with a controllable excitation field is proposed. Such a controlled field will enable the full volt-second capability of the induction coil to be utilized, so that in a Tokamak application one may achieve burn times twice as long compared to the case of a constant-excitation HMG. For a drum type HMG, it is shown that by placing iron yokes both interior to and around the rotor drums and by proper selection of machine geometry, it is possible to reduce the magnetic energy stored in the excitation coils without excessively increasing the weight and cost. A unit cost of $6.74/kJ was computed for a machine with total inertial energy of 1500 MJ and a magnetic energy of 96.2 MJ.