A versatile laboratory electromagnet with HTS coils

We report the development of a laboratory electromagnet utilizing high temperature superconducting (HTS) coils which is designed to generate fields in excess of 3 Tesla, but with power consumption and size significantly below that possible with copper-wound coils for an equivalent useful field volume. The components are complete and the system is currently being assembled. The electromagnet is based around a compact iron yoke with four HTS double pancake coils, employing a total of 1.6 km of first generation HTS (Bi-2223/Ag composite) wire, to generate the field across an air-gap of 50 mm. The electromagnetic design was tailored to take into account the anisotropic in-field performance of the HTS conductor, requiring a minimization of the radial field component at the coils while retaining sufficiently open access for installation of the components of a vibrating sample magnetometer with which this magnet will be used. The HTS coils are conduction cooled with a single-stage cryocooler that delivers approximately 27 W of cooling power at the design operating temperature of 35 K; HTS current leads are employed to reduce the thermal load at the coils. In the present configuration the coils are housed in a single cryostat, but the design is easily adaptable to provide for a number of specific application requirements. Contrary to the generally held view that HTS magnets are still too expensive, this project demonstrates that utilization of HTS conductor is now an attractive option in a number of application areas.