Basic approach to high-critical temperature superconducting bulks and their applications.

It is first pointed out that feasible bulk current density in superconductors is restricted not only by weak couplings between sub-structures but also by electro-magnetic properties such as flux creep and flux jump. The processing of bulk YBCO is outlined with a view to improving critical-current density, while the limited level of the current density due to the undesirable phenomena is presented. Experimental and theoretical works for the prospective applications of high-critical temperature bulk superconductors are summarized.