DRAWING

Electrical obstacles. Temperature is only one of three con-straints on superconductive material; the other two are current density and magnetic field. If the operating point leaves the inside of the "apple slice" shown above, the material snaps out of super-conductivity. Current densities needed for applications like direct storage of electricity lie outside this space by factors of 10 or 100.

If past experience for the transition from laboratory to com-mercialization is any guide, large-scale commercialization of super-conductivity in this century appears very dubious.