Design and Fabrication of the Iron Core for the OHTE Experimental Machine

Abstract

The Ohmically Heated Toroidal Experiment (OHTE) is a toroidal pinch magnetic confinement plasma experiment which has been operating at GA Technologies (GA) since February 1981. In its original form, plasma current was induced by an air core induction or ohmic heating coil driven by a capacitor bank. Preliminary study revealed that greater plasma currents and pulse lengths could be achieved more economically by converting to an iron core rather than by installing additional capacitors. Therefore an iron core with a 3 volt-second capability and a stepped configuration was designed, fabricated and incorporated into the OHTE experimental device as part of a planned upgrade. To facilitate handling and installation, the iron core was fabricated in 28 segments consisting of 14 lower and 14 identical upper segments. Space limitations in the center of the machine created by existing geometry limited the flux path to approximately 1.28 m diameter or 1.296 m/sup 2/. Using a stacking factor of 90% and allowing 3 mm between segments results in a true iron cross section of 1.12 m/sup 2/. Each segment was fabricated by continuously winding in a ''clockspring fashion'' around a hardwood former Armco electrically oriented steel, 0.35 mm thick and 88 mm wide. Interspacedmore » between laminations is insulating paper 0.02 mm thick and 88 mm wide bonded to the steel using a structural epoxy adhesive continuously applied during winding. After winding and curing, support saddles consisting of hardwood and aluminum were bonded to the segments. The segments were then cut into two identical halves on a large vertical milling machine. To eliminate electrical shorts, all machined surfaces were etched with a dilute nitric acid solution, then painted with a moisture repelling high dielectric strengt epoxy spray paint to eliminate lamination to lamination creepage and surface corrosion.« less