BPX toroidal field coil design

Abstract

The toroidal field coil system of the Burning Plasma Experiment (BPX) consists of 18 beryllium copper magnets arrayed in a wedged configuration with a major radius of 2.6 m and a field strength capability on axis of 9.0 T. The toroidal array is constructed from six 3-coil modules to facilitate remote recovery in the event of a magnet failure after nuclear activation precludes hands-on servicing. The magnets are of a modified Bitter plate design with partial cases of type 316-LN stainless steel welded with Inconel 182 weld wire. The coil turn plates are fabricated from CDA C17510 beryllium copper with optimized mechanical, thermal, and electrical characteristics. Cryogenic cooling is used to reduce power dissipation and to enhance performance. The magnets are cooled between experimental pulses by pressurized liquid nitrogen flowing through channels in the edges of the coil turns, allowing one full-power pulse per hour. Overturning forces are reacted by friction forces generated by the wedging pressure in the central leg regions and by case and structure in the other regions of the coil. The magnets are designed to structural design criteria modeled after the ASME Boiler and Pressure Vessel Code, Section III, but with appropriate changes.<>