Bulk high temperature superconductors for magnet applications

A summary is given of the various techniques used to prepare melt processed YBCO. The use of these materials as permanent magnets is discussed. Since nearly all applications involve demagnetizing fields of some kind, these are compared with the equivalent ferromagnetic material. Superconductors behave in the opposite way to ferromagnets in that a reversed field can increase the magnetization, while a field parallel to the magnetization quickly reduces it to zero. Then ways of obtaining maximum repulsion and attraction without demagnetizing the sample are described. A summary of the forces and torques available is given. In particular, it is shown that YBCO can provide extremely high current densities in rotating machines. (C) 1997 Published by Elsevier Science Ltd.