The engineering and final assembly of S-1 Spheromak Flux Core

The Flux Core of the S-1 Spheromak (Figure 1) is a torus with a major radius of 1m and a minor radius of 19 cm. The primary elements within it are the PF and TF (Poloidal and Toroidal) windings which are a water cooled copper cable, two turns of EF (equilibrium Field) coils, and an epoxy-glass mandrel to support them. Surrounding these are an aluminum shell, potting material, and a thin, highly resistive Inconel liner which is a vacuum boundary. After the winding of the TF cables (see previous report for 9th Symposium), a built-up layer of dry interwoven fiberglass tape was wound around the entire flux core. The fiberglass, when vacuum impregnated, provides structural support. Next, the four piece aluminum shell which also served as an enclosure for vacuum impregnation was applied. The epoxy used in this operation was cured at low temperature to insure integrity of the PF/TF polyethylene insulation. After impregnation, a wet layup of fiberglass/air cure epoxy was wound over the aluminum shell for further structural support. The Inconel liner, which had been spun, ground, and chem-milled to a 0.254 mm thickness, was welded in position about the circumference at the midplane. A midplane band of 2.286mm thickness was left for this purpose along with elements to provide for closure welding of vacuum feedthru assemblies. The annulus between the liner and fiberglass/ epoxy structural wrapping was then pressure potted with urethane. This material was chosen because it would bond to the Inconel and fiberglass yet would allow for thermal expansion. The completed flux core was then installed between the domes of the S-1 vacuum vessel. Initial testing of S-1 indicates that the fabrication techniques have proven successful. A detailed description of the fabrication, installation, and testing will follow