Applications of superconductors

Superconductors have been applied to develop train systems that operate with magnetic-levitation (MAGLEV) in which the train effectively travels RJlOmm above its tracks, i.e. virtually frictionless motion. The first commercial train came into service in Shanghai in 2003 and can reach speeds of 440 km h.  

For the development of applications for superconductors, two obstacles in particular have to be surmounted. The first is that the material must be cooled to low temperatures to attain 7),. As higher temperature superconductors are developed, this has become less of a major drawback, but still militates against the use of superconductors in conventional settings. The second problem is one of fabrication. When prepared as a bulk material, the cuprate superconductors have unacceptably low critical current densities, i.e. the superconductivity is lost after the material has carried only a limited amount of current. The origin of the problem is the presence of grain boundaries in the solid 

In 1911, Onnes reported the first superconducting metal, mercury. 7c for Hg is 4.15 K. Sketch a graph of what Onnes observed upon cooling Hg below 4.5 K, given that the resistance of the sample in the experiment was 1.3 Q at 4.5 K. 

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In addition to a critical temperature and critical field, all superconductors have a critical current density, Jc, above which they will no longer superconduct. This limitation has important consequences. A logical application of superconductors is as current-carrying media. However, there is a limit, often a low one, to how much current they can carry before losing their superconducting capabilities. The relationship between Jc, He, and Te for a Type II superconductor is shown in Figure 6.32. Notice that the Hc-Tc portion of this plot has already been presented in Figure 6.10 for a Type I superconductor. 

Rediscovery. The topic and potential of superconductivity essentially was rediscovered in the late 1970s and early 1980s, during which period the research activity safely can be described as zealous. This was fueled by the scores of probable applications of superconductors, but which to date largely remain as promises. Research continues at a good pace, and the topic is much better understood as compared with a decade ago. As pointed out later m this article, much excellent technological fallout has occurred from many millions of dollars invested in research. The search for the ultimately practical superconductor, although still elusive, has reinforced tiie multidisciplinary sciences involved, notably physics and chemistry. 

Another current application of superconductors is superconducting quantum interference devices or SQUIDs. These devices can measure magnetic flux with an extremely high sensitivity, which is particularly useful for many purposes. The basis of such a high sensitivity is the... 

Potential applications of superconductors are based on the properties that these materials present (i) zero resistance below Tc, (ii) Josephson effect, (iii) Meissner effect, and (iv) superconducting magnets. 

Table 9.8 Important contemporary and potential applications of superconductors. 

Investigate current and proposed technological applications of superconductors. Find out which of these applications have been successfuUy tested or are already in use. 

Potential applications of superconductors include electrical transmission (little or no heat loss in wires) and energy-efficient transportation (magnetically levitated trains, etc ). 

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