The Design of Homopolar Motor-Generators for Pulsed Power Applications

The need for inexpensive pulsed power for fusion research is becoming more intense as the size of these experiments rapidly increases. Nearly all experimental investigations now proposed require energy stores of hundreds of megajoules and some proposed reactors are in the gigajoule range. An engineering feasibility study at the University of Texas at Austin in 1972 suggested the use of a Faraday disc or homopolar machine for inertial energy storage. Such a machine can use a single rotor as the motor and generator armature as well as the flywheel at a considerable cost saving relative to separate units. A number of machines using this principle have been designed by the Energy Storage Group at the University of Texas at Austin and two have been built and tested. Both the 0.5 megajoule and 5 megajoule homopolar machines, built at the University of Texas at Austin, have exceeded their original performance goals. Initially the main advantages of such homopolar machines appeared to be the geometric simplicity of the field coil windings, the use of a rotor without windings, and the resultant low cost. At present another advantage seems to overshadow these in that rotors without windings can be rapidly accelerated to high speeds and can be discharged rapidly with an electrical release of virtually all of the inertial energy in time periods down to milliseconds. Present design studies and experimental research are concentrating on producing low inductance, low resistance, high speed machines with short current diffusion times. Current collectors for use at high speed (up to 450 m/sec) are under experimental investigation in a separate brush test facility. These studies and tests are summarized in a form to facilitate determining the compatibility of homopolar machines and specific loads.