Description of Pulsed Homopolar Generator Technologies for a Fusion Ignition Experiment
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The concept for a single-turn tokamak experiment IGNITEX 1 makes possible the realization of a controlled, self-sustained fusion reaction in the near term with relative simplicity and low cost. The IGNITEX tokamak utilizes low-impedance toroidal field (TF) and poloidal field (PF) magnet systems which induce the high-level fields and currents required for fusion ignition. These magnet systems require power supplies that can meet strict operational conditions. Homopolar generators (HPGs) are well suited for operation of a single-turn tokamak because they are inherently high current, low voltage machines which can kinetically store all the energy required for a pulsed discharge. The energy storage is accomplished in a compact manner by using high speed composite flywheel technology and provides the added advantage of keeping electrical grid power requirements very low. Finally, since HPGs are simple de machines, their cost is low and rectifier systems are not necessary. In this paper, the HPG technologies to be utilized in a fusion ignition experiment are described. The various components, materials, and design considerations for the HPG current-collection systems are reviewed, including rotor slip ring, brushes, and actuators. Design, fabrication, and assembly techniques for the lightweight, composite, energy-storage flywheel are given. The status of these HPG technologies relative to IGNITEX power supply requirements are reviewed. The modes of operation of the TF and PF magnet systems are analyzed. Questions of reliability of operation, maintenance, and cost evaluation are also addressed. Finally, the construction and testing of a full-scale prototype IGNITEX HPG power supply module is proposed.