Wires and Tapes
Multi-tesla, high-field superconducting magnets are possible only when a superconductor can be made into a wire or tape conductor form hundreds of meters or even kilometers long with high current density, acceptable strength, high critical field and affordable price. Thousands of materials are superconducting, yet only six, Nb47wt.%Ti (Section 11.2), Nb3Sn (11.3), Bi2Sr2CaCu2O8−x and (Bi,Pb)2Sr2Ca2Cu3O10−x (11.4), YBa2Cu3O7−x, or more generally any rare-earth (RE) variant of YBa2Cu3O7−x (11.5) and MgB2 (11.6), are available commercially as conductors. Chapter 11 describes many aspects of the development and property evolution in these six conductors, this opening Section 11.1 concentrating on the reasons why the well-developed vision of superconducting magnets of 1913 actually took almost 50 years to implement. It is in many ways a truly remarkable story that intersects with some of the most heartening and terrible aspects of 20th century science and politics. We can define several eras that have governed the development of conductor technology:
• Onnes’s vision for superconducting magnets — 1913 • Alloyed superconductors, the type I and type II transition and the collective failure to under-
stand it — 1930-1960
• Theoretical developments and their disconnect from experiment — 1930-1957 • High current density, high field superconductors — 1960 on • Coexistence of high temperature and low temperature superconductors — 1987 on • Superconducting conductors beyond the Centennial — 2011 on.