Design and construction of a small-scale layer-wound no-insulation (LW-NI) insert magnet with REBCO-coated conductors operating in a background magnetic field exceeding 15 T

Rare-earth-based barium copper oxide (REBCO) coated conductors have shown impressive performance in current transport capability and mechanical force tolerance in high magnetic field conditions, so their application as layer-wound insert magnets for the construction of a high-field nuclear magnetic resonance (NMR) superconducting magnet is reasonably expected. However, the inhomogeneous stress distribution induced by the screening current, coupled with significant vertical magnetic field exposure at the end of the magnet, poses threats to the mechanical stability of the layer-wound insert magnet. Meanwhile, the quench protection in REBCO magnets is a critical problem; adopting no-insulation winding methods can provide the magnet with self-protecting capability. To verify the feasibility of the manufacturing process for the layer-wound magnet and to accumulate technological experience for the subsequent construction of NMR magnets, a layer-wound no-insulation (LW-NI) insert magnet was fabricated with REBCO-coated conductors. The winding has an inner diameter of 40 mm, an outer diameter of 42 mm, and a total height of 66 mm; nine layers of the insert magnet were wound with 16 turns per layer. The layer-wound magnet successfully energised with a current of 480 A (1 µV/cm quench criterion) and generated a self-field of 1.13 T in the axial direction of the magnet in an external 14 T background magnetic field (15.13 T in total) at 4.2 K.