Coil fabrication of the UST_1 modular stellarator and potential enhancements

Physics of stellarators has been optimized up to excellence levels. In contrast, optimization and innovation in the engineering and construction of stellarators is still comparatively modest. Particularly for stellarators but also for tokamaks, geometric complexity, small dimensional tolerances and large size currently imply relatively high fabrication costs, delaying the evolution of the stellarator research line and also hindering tokamaks. In this framework, the small low-cost modular stellarator UST_1, built and operated in a private laboratory, may contribute to the background of cost-reasonable construction methods for small fusion devices, particularly stellarators. The paper summarizes the engineering development and fabrication of UST_1 coils and outlines possible engineering R&D lines for the enhancement of the UST_1 construction methods. UST_1 consists of 12 resistive modular coils wound in grooves mechanised on a single monolithic toroidal frame surrounding the vacuum vessel. A special milling machine working on toroidal coordinates was developed, tested and built in order to accurately mechanise the grooves in the monolithic frame.

► A construction method for stellarator modular coils is developed and validated.
► Single monolithic grooved coil frame and conductors compressed in groove.
► Modular coils fabricated by a milling machine working on toroidal coordinates.
► Positioning and metrology of independent coils and winding fasteners are avoided.
► Rapid prototyping and one turn per groove may improve the construction method.