As mentioned briefly in the introduction, the potential of superconductors is incredible, and their applications are practically innumerable. They promise to revolutionize electronics as we know them today: making logic gates faster, smaller, and more efficient. This will lead to a leap in miniaturization of consumer electronics and integrated circuits. At the very heart of this is Josephson Junctions, explained below.
Josephson Junctions have already proven their worth. Recently, the accepted value of Planck's constant has changed from 6.62559 to 6.626196E-34 by experiments on Josephson Junctions measuring the voltage across the junction and the frequency of radiation.
Already widely used, SQUIDS (Superconducting Quantum Interference Device) are made from a pair of Josephson Junctions (pictured below). A biasing current is maintained in the SQUID, the voltage measured across the device oscillates with the changes in phase at the two junctions, which is dependant on the changing magnetic flux. Therefore, by counting oscillations, you can detect the flux change. Using this principle, SQUIDS can detect magnetic fields as low as 10E-14 T. Examination of Josephson Junctions like this has led to the discovery that magnetic flux is quantized.
Many properties of superconductors and Josephson Junctions make them ideal for logic gates. Perhaps foremost, such gates have been shown to have a switching time of 10ps. However, that is so fast- almost too fast- that it leads to problems- mainly because of the finite velocity of light. In such an incredibly short time interval, an electrical signal will have only traveled 3mm. This makes density of components quite important, as to minimize the distance between elements. In traditional electronics, this would create a heat dissipation problem, and since we're dealing with temperature-sensitive superconductors, this is even more of an issue. Fortunately, superconducting elements dissipate heat many orders of magnitude less than traditional electronics.
Another application already being exploited is using Type II superconductors in electromagnets to create very large magnetic fields. Fermilab is currently using superconducting electromagnets capable of 4.5T in its particle accelerator. Using superconductors in its final stage of acceleration, it has accelerated particles to energies up to about a million MeV.
Other applications involve the exploitation of the Meissner effect to create frictionless suspension systems. A magnetic rotor suspended above a superconducting stator would be almost completely frictionless. More so, if the magnetic rotor is pushed towards the stator, the levitative force will increase because of the increase in flux density. An exotic use suggested has been for the azimuth mount for a lunar-based telescope, since such a mount must stand up to extreme cold (lower than Tc, naturally) and dust, this application would fit nicely. A more traditional (and somewhat obvious) use is in a traditional electric motor. Using superconducting bearings and superconducting coils, it is possible to get close to a 100% efficient motor, since virtually no dissipative friction or resistance occurs.
Mag-Lev trains are also a possibility in the near future. In 1979 a Japanese mag-lev train set a speed record of 321 mph. Like most trains imagined, the Japanese train had superconducting magnets on the cars themselves, inducing currents in the rails, and creating a repulsive force to levitate the train. Though such a setup requires that the train be moving before it levitates, mag-lev trains should be much safer than traditional trains at high speeds.
One of the most natural applications is to power distribution- since 10-15% of power is dissipated through resistance, superconductive power lines are enticing. In fact, many of the systems designed to overcome resistance in long-range power distribution can be eliminated, such as multiple transformers and high voltage AC. Perhaps Tesla's legacy of alternating current will soon fade as power transmission becomes superconductive. However, there are a lot of hurdles to overcome, including material sensitivity, brittleness of ceramics, and the need to cool to liquid nitrogen or liquid helium temperatures. Despite the infancy of high temperature superconductors, the industry is optimistic and is embracing the technology. The global leader is American Superconductor, and power systems have already begun to convert to superconductive systems.
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TJ Barry MMIII