The utilization of composites layered on an additive manufactured substrate, for the production of coil supports for modular coils in small or middle size experimental stellarators is assessed. The focus of the study is a monolithic coil support comprising the coils of a half-period of a stellarator, somewhat similar to the ones in UST_2 and ARIES-CS stellarators. However, the concept may be applicable to quasi-monolithic coil supports (coil forms of NCSX type) or individual coil casings (W7-X type). Coil supports for stellarators require high precision, stiffness and strength for large contorted parts. Traditionally, monolithic coil supports are produced by steel casting/forging and final machining. This production method and material gives accurate, stiff and strong coil supports, but the method may be expensive for monolithic supports due to the geometrical complexity and required accuracy of the structure. In relation to those matters, this work investigates whether a monolithic coil support comprising an additive manufactured resin substrate, which is externally (outward from the coils) surrounded with a thick layer of fibre-reinforced resin, may achieve enough strength and stiffness under middle/high magnetic fields. Finite element calculations are produced to obtain the direction of the principal stresses and their values in compression and tension at different areas of the monolithic support, which is relevant for anisotropic materials. The feasibility of directional application of (carbon) fibres on the winding surface of the stellarator outward from the coils is experimentally tested on a scaled-down additively manufactured prototype of a monolithic support. The strength and stiffness of the composite structure appears sufficient for common magnetic fields in experimental stellarators, and the 3D-composite design and manufacturing was technically feasible.
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The laminate composite reinforcement is produced on an additively manufactured hollow plastic frame (internally reinforced with cast short-fibre epoxy resin). The fibre layers are located on flexible copper conductor which is wound in each of the 12 grooves of the half-period frame (three turns per coil), Fig. 5 . The conductor is wound from the outside of the monolithic frame, having the outward Lorenz forces supported by the external layer of composite. Winding from the outside of the frame is a positive property of the alternative of composite monolithic support.
This work has been funded by the Spanish ‘Ministry of Science, Innovation and Universities’ and the ‘Fondo Europeo de Desarrollo Regional’ (FEDER EU) under contract number RTI2018-098356-B-I00, project ‘Study of additive and advanced manufacturing for high magnetic field fusion devices of stellarator type’.
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- Additive manufacturing