Applications

Power Transmission

One of the most obvious applications of superconductors would appear to be to exploit its zero resistance in making current carrying wires to transport electrical energy. Currently overhead power transmission lines lose about 5% of their energy due to resistive heating. In relative terms this does not seem like a large amount but, due to the vast amount of power that is delivered, this equates to large wastage in real terms.

Clearly this technology has not yet been realised as there are not superconducting wires transmitting power on a commercial scale. A commercially viable superconducting wire must have as high a critical temperature as possible as well as be able to handle significant current densities. However the mechanical properties of the material must also be considered when designing a wire to ensure it is resilient and flexible enough to be used as a replacement for conventional copper wires. This means that the high temperature ceramic superconductors that have recently been discovered are often not yet best suited for this purpose.

In large scale applications, alloys of niobium and titanium tend to be used. These require liquid helium coolant which adds to the cost of running. The wires also have to be much larger than expected in order to avoid what are known as “quenches”. These occur if the wire momentarily stops being superconducting and returns to its normal state. Such a quench creates a region of high electrical resistance and rapidly dissipates a large amount of energy. This can lead to some part of the wire being vaporised, thus destroying the functionality of the wire.

Currently the cost of manufacturing the superconducting wires as well as the cost incurred in maintaining liquid helium temperatures prohibits the use of superconductors in the transmission of power in a commercial environment.

Magnetics

One of the most successful applications of superconductors is in the production of very large magnetic fields. Here superconducting wires are wound into a coil and a high electrical current is passed along the wire in order to produce very high field strengths.

One of the most important applications which require a very high magnetic field is in Magnetic Resonance Imaging (MRI). This technique uses the high field to split the degenerate spin state of a hydrogen nucleus, which can then be investigated using electromagnetic radiation in the radio wave region. This allows the machine to image two dimensional cross sections which have hydrogen atoms in different chemical environments. As the body contains many hydrogen atoms present in water, different tissues in the body give different signals. These two dimensional slices can be built up to form complete pictures of the area of the body being imaged.

Another area which exploits the high field strengths that can be achieved using superconducting magnets is in high energy physics. High strength magnets are key components in particle colliders used to probe the most basic constituents of matter. They are used to deflect high velocity charged particles to keep them in a circle and allow them to be constantly accelerated. High strength magnets are also used in fusion research to contain plasmas. This high temperature state of matter cannot be contained in conventional materials and must be levitated and enclosed using high strength magnets.

Another application making use of superconductors to produce magnetic fields which is already in use is for magnetic levitation (maglev) trains. There are working examples of this technology in use in both Germany and Japan. The animation below outlines the two basic designs of maglev trains and describes how they work.

Electronic Applications

Current microelectronics are beginning to be limited by the speed at which heat can be removed which is produced by the electronic circuits. In order to speed up computing power, interconnects between various components of the circuit can be shortened. However, this creates even more heating problems due to the higher current densities which have to be used. Superconducting wires could eventually be used to remove resistive heating and help solve this problem.

Current silicon based technology is also limited by the speed at which transistors can switch between their 0 and 1 states. Superconducting junctions can be made by exploiting a phenomenon known as the Josephson effect (which is not covered in this TLP) which allows for much greater switching speeds and could greatly increase computer processing speeds.

The Josephson effect is also exploited in making Superconducting Quantum Interference Devices (SQUIDs). These devices allow exceptionally small magnetic fields to be measured and are so sensitive that they can measure the tiny magnetic fields produced by the currents that flow along nerve impulses. This allows for a powerful new technique in neurological research and investigations of the brain.