New Perspectives on the Physics of High-Field Superconductors

Abstract

In making a practical high-field superconducting conductor, the manufacturer is confronted with the problem of optimizing simultaneously several properties (e.g., T_c, H_c2, J_c, and mechanical behavior), all of which themselves depend on a variety of material parameters. At the same time it is necessary to fabricate the conductor in the form of fine, twisted filaments imbedded in a normal metal matrix. This is no simple matter, needless to say, and in carrying out such a task it is helpful to have as clear an understanding as possible of how the physical properties of interest depend on the various material parameters. In this paper we review recent advances in the understanding of the upper critical field, H_c2, of real high-field superconductors in an effort to provide some improved guidance to the practical conductor community in just this regard. In particular, we address the role of disorder in determining H_c2 of the A15 superconductors and corrections to the theory of Pauli limiting that have come to light recently. The insights obtained from these results are also used to provide an up-to-date set of ground rules for optimizing H_c2 and to establish expected theoretical limits of H_c2 in superconductors of practical interest.

Invited paper.

Work supported by the Department of Energy.