Embedded conductors in solidified molten metal for winding packs for high-field stellarators

Abstract

The potential advantages of high-field stellarators are currently being recognised, as previously happened with tokamaks. However, the winding packs and the electrical insulation of the conductors in high-field stellarators require particularly high strength, and still keeping the dimensional accuracy and long-term positioning of the conductors in contorted coils. Radial plates in ITER, and stacked conductors with strong metallic jacket and internal insulation in FFHR heliotron have been validated and studied. However, radial plates for modular stellarators still require further studies and validation due the extreme accuracy required for the grooves in contorted plates, which increases with the number of turns per pancake.A third alternative is studied and experimented in this work. The concept implies casting a strong low-melting point metal in-between conductors, which are properly wound on a supporting structure. Thus, after solidification, the conductors (acting as inserts in a mould) and the metallic alloy act as a single solid structure. Essentially, the concept aims at relaxing the required accuracy in radial-plate grooves and to create a solid structure without spaces amongst conductors and without insulation external to the conductors. Therefore, a large number of conductors per winding pack may be created, which decreases certain stresses in the insulation and conductor. The drawbacks and difficulties found for this approach during the experiments with a scaled-down prototype are also presented and discussed.