Turn-to-turn friction enhancement in high-temperature superconducting coils for mechanical stability under lorentz force

Abstract High-temperature superconducting coils subjected to ultra-high magnetic fields undergo mechanical deformation due to the Lorentz force generated by the magnetic field. Recent attempts to prevent this deformation have proposed the use of overbanding technology, which entails surrounding the outermost turn of the coil with a high-strength material such as stainless steel, as an optimal alternative. However, the disadvantage of overbanding in terms of thermal/electrical protection of the coil has been emphasized because the stainless steel surrounding the coil reduces the operating efficiency of the coil by preventing the dissipation of joule heat and current when quenched. In this study, our approach to prevent the deformation of the coil without applying such overbanding was to intentionally abrade the surface of the high-temperature superconducting tape using sandpaper with different friction coefficients. This enabled us to fabricate coils with different turn-to-turn friction forces, which prevented the deformation of the coil by using the turn-to-turn friction force generated by the abrasion. The electromechanical tests we performed on the coil in a liquid nitrogen bath (77 K) confirmed that, compared to the coil without surface treatment, the coils fabricated by abrading the surfaces of the high-temperature superconducting tape exhibited decreased deformation even when the same Lorentz force was applied.