Editing Superconductivity (section)

=== Niobium ===
The first practical application of superconductivity was developed in 1954 with [[Dudley Allen Buck]]'s invention of the [[cryotron]].<ref name="mit-memo2">{{cite web |last1=Buck |first1=Dudley A. |title=The Cryotron – A Superconductive Computer Component |url=http://dome.mit.edu/bitstream/handle/1721.3/40618/MC665_r15_M-3843.pdf |access-date=10 August 2014 |publisher=Lincoln Laboratory, Massachusetts Institute of Technology}}</ref> Two superconductors with greatly different values of the critical magnetic field are combined to produce a fast, simple switch for computer elements.

Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G. B. Yntema<ref>{{cite journal |author=Yntema |first=G. B. |date=1955 |title=Superconducting Winding for Electromagnet |journal=[[Physical Review]] |volume=98 |issue=4 |page=1197 |bibcode=1955PhRv...98.1144. |doi=10.1103/PhysRev.98.1144}}</ref> succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, [[John Eugene Kunzler|J. E. Kunzler]], E. Buehler, F. S. L. Hsu, and J. H. Wernick<ref>{{cite journal |author=Kunzler |first1=J. E. |last2=Buehler |first2=E. |last3=Hsu |first3=F. L. S. |last4=Wernick |first4=J. H. |date=1961 |title=Superconductivity in Nb3Sn at High Current Density in a Magnetic Field of 88 kgauss |journal=Physical Review Letters |volume=6 |issue=3 |pages=89–91 |bibcode=1961PhRvL...6...89K |doi=10.1103/PhysRevLett.6.89}}</ref> made the startling discovery that, at 4.2 kelvin, [[niobium–tin]], a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. The alloy was brittle and difficult to fabricate, but niobium–tin proved useful for generating magnetic fields as high as 20 tesla.

In 1962, T. G. Berlincourt and R. R. Hake<ref>{{cite journal |author=Berlincourt |first1=T. G. |last2=Hake |first2=R. R. |name-list-style=amp |date=1962 |title=Pulsed-Magnetic-Field Studies of Superconducting Transition Metal Alloys at High and Low Current Densities |journal=Bulletin of the American Physical Society |volume=II-7 |page=408}}</ref><ref>{{cite journal |author=Berlincourt |first=T. G. |date=1987 |title=Emergence of Nb-Ti as Supermagnet Material |url=http://fs.magnet.fsu.edu/~lee/superconductor-history_files/Centennial_Supplemental/11_2_Nb-Ti_from_beginnings_to_perfection-fullreferences.pdf |journal=Cryogenics |volume=27 |issue=6 |pages=283–289 |bibcode=1987Cryo...27..283B |doi=10.1016/0011-2275(87)90057-9}}</ref> discovered that more ductile alloys of niobium and titanium are suitable for applications up to 10 tesla. Commercial production of [[niobium–titanium]] supermagnet wire immediately commenced at [[Westinghouse Electric Corporation]] and at [[Wah Chang Corporation]]. Although niobium–titanium boasts less-impressive superconducting properties than those of niobium–tin, niobium–titanium became the most widely used "workhorse" supermagnet material, in large measure a consequence of its very high [[ductility]] and ease of fabrication. However, both niobium–tin and niobium–titanium found wide application in MRI medical imagers, bending and focusing magnets for enormous high-energy-particle accelerators, and other applications. Conectus, a European superconductivity consortium, estimated that in 2014, global economic activity for which superconductivity was indispensable amounted to about five billion euros, with MRI systems accounting for about 80% of that total.