Superconductors_and_Bcs_Theory

Superconductors BCS Theory of Superconductivity Superconductivity is when certain metals (e.g. Mercury), alloys (e.g. (Tl5Pb2)Ba2MgCu10O17+) and ceramics (e.g. yttrium barium copper oxide ceramic) conduct electricity without resistance. Superconductivity is possible in known metals and alloys at temperatures near absolute zero where as some ceramics are able to become super conductors at temperatures as high as -148 degrees Celsius. The phenomenon of superconductivity can be explained using the BCS theory. Developed in 1957 by American physicists, john Bardeen, Leon cooper and J. Robert Schrieffer, explains that the resistance of metal is due to collisions between free electrons and impurity atoms or imperfections in the crystal lattice. Superconductors however allow electrons to go through unimpeded. This is because of an attractive interaction between it’s electrons that allow them to form cooper pairs. These cooper pairs are held together and flow without resistance the lattice. Uses for Superconductors Superconductors have a variety of uses. Some examples of these are; • Maglev (magnetic levitation) train: These work because the track is a superconductor with a current moving through it which produces a magnetic field that repels the magnetic field produced by an electromagnet in the train, allowing it to hover above the track. The benefits of Maglev trains in comparison to other forms of transport include: 1. It is cheaper, faster, not congested, and has a much longer service life. They can transport tens of thousands of passengers per day along with thousands of piggyback trucks and automobiles. because there is no mechanical contact and wear, and because the weight is uniformly distributed, rather than concentrated at the wheels there is less wear and tear in need of repair. They can move at speeds around 300 mph. 2. Better for the environment. Instead of burning fossil fuels Maglev consumes energy which can be generated by nuclear, solar, hydro or turbine means as a substitute to coal dependent sources. 3. Less obtrusive. They’re much quieter than average trains and only run on a narrow elevated beam so they take up less space than a train track. 4. Safer. No chance of colliding with other vehicles. The distance between Maglev vehicles on a guideway, and the speed of the vehicles, are automatically controlled and maintained by the frequency of the electric power fed to the guideway. • Large hadron collider or particle accelerator: Superconductors are used to create powerful electromagnets to accelerate particles to near light speed. The hadron collider is used by physicists to study atoms. This is done by shooting two beams of subatomic particles being either protons or lead ions, in opposite directions within a circular accelerator which gain energy with every lap. The Large Hadron Collider is used to recreate the conditions after ther Big Bang by allowing the beams to go into a head-on collision with each other at high energy. The particles that then occur after the collision are analysed through many experiments. • SQUIDS (Superconducting Quantum Interference Devices): These are used to detect even very weak magnetic fields. They are used to in equipment with the purpose of detecting and removing mines. SQUIDS have been a prime factor in saving the lives of Australian and American troops hostile territories. “E-Bombs”: these devices make use of superconductor derived magnetic fields in order to produce a fast, high intensity magnetic pulse that interferes or disables electronic equipment. These can two billion watts of energy at once. The duration of these blasts are short however so that they don’t burn or affect people or buildings making them highly desirable when enemies are working within civilian areas. Other uses under development include: Making electricity generation more efficient: Because less energy will be lost to friction. Very fast computing: This is because by replacing the semiconductor switches with superconductor switches, they could operate up to ten times faster. Limitations in Superconductor based technology The major limitations in using superconductors are in the difficulty of achieving and maintaining the low temperatures needed for them to work as superconductors. Liquid nitrate can be used but to obtain enough for big projects such as power transition would be very expensive and running liquid nitrogen through a consumers hand held device is impractical. Superconductors are also very brittle and hard to manufacture making them difficult to manipulate as a wire. If a superconductor could be accessed that worked at room temperature and was less brittle, the majority of these issues could be overcome. The another limitation to superconductors is that they are very sensitive to a changing magnetic fields, meaning that AC current would not be able to work effectively with superconductors. Devices such as transformers, which only work with an AC current, would be more difficult to implement. The Benefits of Superconductors in Generators In generators, because Superconductors would have reduced energy losses (due to there being no resistance therefore any energy lost to heat) less coal and other fossil fuels would be necessary. Generators wound in superconducting wires could generate the same amount of energy but the equipment wouldn’t need to be nearly as large to do so. A magnetic core would also be unnecessary. This is because you could use an air core or permeability core and still achieve very high flux densities. If a material that superconducted at room temperature was used there would be less cooling needed for there would be next to no heat generated from friction and less transmition losses would occur. Bibliography 1. World Book (1999) 2. http://www.superconductors.org/Type2.htm 3. http://www.britannica .com/EBchecked/topic/131690/conductive-ceramics/76755/superconductors 4. Excel HSC Physics 5. http://www.rsc.org/Education/Teachers/Resources/Inspirational/resources/4.5.2.pdf 6. http://www.21stcenturysciencetech.com/articles/Summer03/maglev2.html 7. http://public.web.cern.ch/public/en/lhc/lhc-en.html 8. http://www.pcmag.com/article2/0,2817,1130724,00.asp 9. http://www.craville.110mb.com/physics/superconductors.htm#Limitations_of_Superconductors:_ 10. http://www.craville.110mb.com/physics/superconductors.htm#Motors_and_Generators: 11. Dr Terrence James Summers