A RESEARCH INVESTIGATION OF THE FACTORS THAT AFFECT THE SUPERCONDUCTING PROPERTIES OF MATERIALS

The extension of the critical state model (Bean model) of the homogeneous type II superconductor to include alternating field excitation, alternating current excitation, and rotating field excitation is reported. The alternating current and alternating field losses in intermetallic high critical current density superconductors have been measured in several experimental situations and found to substantially as predicted. The surface flux penetration and alternating field losses in niobium have been measured below H sub c 1 as function of temperature, field, and surface preparation. The concepts of the critical state model have been used to determine the conditions necessary for a magnetic instability or flux jump to develop in a type II superconductor. The theory suggests several ways of forestalling or eliminating flux jumps. (Author)