The superconductor revolutions and the (slow) applications evolution

The economic gains to accrue from high-temperature superconductors, assuming operation at 77 K, are assessed. It is found that large-scale applications can be achieved now with conventional (low temperature) superconductors. The economic gains at 77 K are incremental compared to 4.2 K and will not determine whether these technologies are implemented. Use of these large-scale technologies are to be determined by economics, competing technologies, and public policy decisions. Operation at 77 K is promising in the near future for small-scale applications and for applications in space. Recent advances in materials development suggest that high-temperature superconductors may be useful for high field applications at 4.2 K.