DESIGNING HTS COILS FOR MAGNETIC-CIRCUITS

We discuss some of the main considerations involved in the design of H TS coils to operate in liquid nitrogen and provide ampere-turns for ma gnetic circuits in general, and then in particular for a small-scale e lectromagnetic (i.e. attractive) maglev demonstrator. The most importa nt factor affecting design is the sensitive and strongly anisotropic d ependence of HTS tape's critical current on magnetic field. Any succes sful design must limit the field in the windings, especially component s perpendicular to the tape's surface(radial components in the case of solenoids), to acceptably low levels such that local critical current s nowhere fall below the operating current. This factor is relevant to the construction of HTS coils for all applications. A second importan t factor is that the presence of an iron magnetic circuit can greatly alter the flux distribution within the coils from that found when they are in free space. FE modelling has been used to calculate accurate f ield profiles in proposed designs for comparison with short sample I-c (B) data. We present a design for a maglev demonstrator, illustrating how some of the problems, in particular the reduction of radial field components, may be addressed, and describe its predicted performance.