18.1 T cryocooled superconducting magnet with a Bi2223 high-TcTc insert

We have successfully developed a cryocooled superconducting magnet which generates the world’s highest magnetic field of 18.1 T. This conduction-cooled superconducting magnet has a 52-mm room temperature bore. The magnet consists of three sections; a high-TcTc superconducting insert coil, four Nb3 Sn coils, and an outer NbTi coil. Each section was energized by an individual power supply. The superconducting coils are cooled conductively by a Gifford-McMahon–Joule-Thomson (GM–JT) cryocooler with a cooling capacity of 4.3 W at 4.3 K. The ramp-up time to 18 T is 60 min. The high-TcTc insert coil is composed of 25 double- pancake coils using Ag/(Bi,Pb)2 Sr2 Ca2 Cu3 O10 (Bi2223) high-TcTc superconducting tape with stainless steel tape reinforcement. The reinforcement co-winding reduces the effective hoop stress down to 48 MPa, and, hence, Bi2223 tape can be used. The innermost of the Nb3 Sn section is made of an internal-tin-processed Nb3 Sn wire because this wire can withstand high critical current density in high magnetic fields. Other three coils require high mechanical strength. They experience hoop stress of 230 MPa, and in this case, bronze-processed high-strength Nb3 Sn wires were used. The magnet has a distinctive feature, that is the high-TcTc insert coil is replaceable. It indicates that the magnet can be used as a 15.5 T back-up magnet for a new insert coil. A Y123 coil is a candidate for the replacement.