Superconductors An element or compound that will conduct electricity without resistance below acertain temperature is a superconductor. This applies only to direct current electricity andto limited amounts of current. Once it is set in motion the current will flow forever, in aclosed loop of superconducting material. Superconductivity is manifested only below acertain critical temperature and a critical magnetic field which vary with the material used. Before 1986, the highest critical temperature was 23.
Kelvin, which would be -417. 6. F. Temperatures this low were achieved by use of liquid helium, an expensive, inefficientcoolant. Ultra low-temperature operation places a severe constraint on the overallefficiency of a superconducting machine. Superconductivity was first discovered in 1911 by the Dutch physicist HeikeKamerlingh Onnes, who observed no electrical resistance in mercury below 4. 2 K, or-451. 8. F. The phenomenon was better understood only after strong diamagnetism wasdetected in a superconductor by Karl W.
Meissner and R. Ochsenfeld of Germany in 1933. The basic physics of superconductivity, however, was not realized until 1957, when theAmerican physicists John Bardeen, Leon N. Cooper, and John R. Schrieffer advanced thenow celebrated BCS theory, for which the three were awarded the 1972 Nobel Prize inphysics. The theory describes superconductivity as a quantum phenomenon, in which theconduction electrons move in pairs and show no electrical resistance.
In 1962 the Britishphysicist Brian D. Josephson examined the quantum nature of superconductivity andproposed the existence of oscillations in the electric current flowing through twosuperconductors separated by a thin insulating layer in a magnetic or electric field. Theeffect, known as the Josephson effect, subsequently was confirmed by experiments. Because of the lack of resistance of superconductors, they have been used tomake electromagnets that generate large magnetic fields with no energy loss. Superconducting magnets have been used in diagnostic medical equipment, studies ofmaterials, and in the construction of powerful particle accelerators.
By using the quantum effects of superconductivity, devices have been developed that measure electric current,voltage, and magnetic field with unprecedented sensitivity. IV. Uses for Superconductors: In the field of biomagnetism, superconductors can peform a life-saving function. Doctors need a non-invasive means of determining what’s going on inside the human body. By putting a strong superconductor magnetic field into the body, hydrogen atoms thatexist in the body’s water and fat molecules are forced to accept energy from the magneticfield.
They then release this energy at a frequency that can be detected and displayed on a computer. Magnetic Resonance Imaging was discovered in the mid 1940’s, and hasrecently become a necessary medical tool with the development of powerful computers toElectric generators made with superconducting wire are far more efficient thanconventional generators wound with copper wire. In fact, their efficiency is above 99%and their size about half that of conventional generators. General Electric has estimatedthe potential worldwide market for superconducting generators in the next decade ataround $20-30 billion dollars.
GE is currently developing a 100-megavolt-ampereprototype to confirm viability. Other commercial power projects in the works that employsuperconductor technology include energy storage to enhance power stability. An idealized application for superconductors is to use them in the transmission ofcommercial power to cities. But, due to the high cost and impracticality of cooling milesof superconducting wire to cryogenic temperatures, this has only happened with short”test runs”. In the electronics industry, ultra-high-performance filters are now being built.
Since superconducting wire has near zero resistance, even at high frequencies, many morefilter stages can be employed to achive a desired frequency response. This translates intoan ability to pass desired frequencies and block undesirable frequencies in applicationssuch as cellular telephone systems. Superconductors have also found widespread applications in themilitarySuperconductors are being used by the US NAVY to detect mines and submarines. And, significantly smaller motors are being built for NAVY ships using superconductingwire and “tape”.