MAGNETS

The main reason why large-scale superconductivity is unlikely to arrive in this century is that the 21^st century is only a scant 11 years away (that's right¾not 12; it starts at midnight of New Year's Eve 1999, not 2000).

Then there are secondary difficulties (beyond the ones enu-merated above) in many of the projects that superconductivity could open up. One of the most promising applications is stronger magnetic fields¾which means a higher field per unit area. To-day's limit is set by the current in the coil that produces the mag-netic field. Go beyond the limit, and the coil just burns up like the wire in a fuse; it can't take the heat. For a given value of current, that heat is proportional to resistance. But superconductive coils have no resistance, and therefore there is no heat. The current can be increased to any value within the apple slice above. That is not unlimited, but a lot more than with a resistive coil.