Oxidized Hastelloy Cloth Insulation for a Wind‐and‐React Processed Ag/Bi2Sr2CaCu2O8 Superconducting Magnet

Practical multifilamentary Ag/Bi2Sr2CaCu2O8 round wires 1 mm in diameter exhibit critical current properties without anisotropy in fields up to 30 T and 4.2 K. We concentrate on the development of a Ag/Bi2Sr2CaCu2O8 insert coil by a wind‐and‐react method for a high field NMR superconducting magnet. Hastelloy cloth was used for the insulation for the wind‐and‐react process. A φ0.05 mm Hastelloy X (Hx) filament was knitted into a braid tube, and has a high mechanical strength and a good tolerance to oxidization at high temperature. We fabricated multifilamentary Ag/Bi2Sr2CaCu2O8 wires with Hx cloth, and heat‐treated them at around 890 °C in an oxygen atmosphere. It was found that the surface of Hx cloth is oxidized enough for a good electric insulation. Multifilamentary Ag/Bi2Sr2CaCu2O8 wires with oxidized Hx cloth insulation have the critical current of 720 A at 4.2 K in a self field.