1 C2C David W. Croft Maj. Kline Engr 310 4 December 1988 Superconductors ABSTRACT Superconductivity allows current to pass through a material with no resistive losses at near absolute zero temperatures. It also exhibits the Meissner effect which causes the superconducting material to repel magnetic fields. The application of this technology has been extremely limited due to the prohibitive costs of using Helium to cool the material to the critical temperatures. Recently, however, new ceramic materials were discovered which exhibit superconductive properties at higher temperatures which can be reached using cheaper liquid Nitrogen cooling. Applications have immediately expanded and are expected to become amazing in the near future as scientists search for a room temperature superconductor. ORIGINS Superconductivity is the passing of electricity through conductors with no loss of power (Graham 17). The resistance of a superconductor is zero. P = I*I*R = 0 where the power P lost in the conductor is equal to the current I squared times the resistance R (which is zero). Superconductivity was first discovered in 1911 when Dutch physicist H. Kamerlingh Onnes was experimenting with materials at near absolute zero temperatures. He was measuring the resistance of a mercury crystal as he lowered the temperature and getting the expected curve of decreasing resistance. Unexplicably, however, at four degrees Kelvin,
2 the resistance suddenly went to zero (Schedter 74). Superconductivity was discovered although a suitable theory was not to be developed for another half century. Progress was slow. In 1973, a niobium and germanium alloy was found to become superconductive at the record high temperature of 23 degrees K. There were few advances beyond this until 1986 even though the benefits of a higher temperature were thought to be enormous. Superconducting technology needed liquid Helium to achieve the low temperatures which was expensive to purchase and maintain as it rapidly evaporated (Graham 18). PHYSICS The most popular theory explaining superconductivity, the BCS theory (named after its authors), is that electrons move through the superconductors in pairs at low temperatures and thus avoid most of the collisions in the conductor which generate unwanted heat (Graham 20). This theory was put forth in 1957, when physicists Bardeen, Coopers, and Schrieffer explained current resistance as a stream of flowing electrons smashing into the fixed crystal lattice of the metal conductor which converts the power into disorganized energy. In superconductivity, they proposed, the electrons attract each other and travel in pairs -- mirror imaging each others actions. When one bangs into the lattice, its partner ricochets, thus regaining the lost energy; the net effect is that no energy is lost in the transmission (Schedter 74).
3 An interesting side effect of superconductivity, the Meissner effect or "magnetic exclusion," is the prevention of magnetic field penetration into the superconducting material. Superconductive materials repel magnetic fields and thus will levitate above magnets (see Fig. 1) (Graham 19). In addition, new discoveries have shown that some materials will hang below a magnet (see Fig. 2). The proposed reason for this is that the magnetic field is pinned in place by impurities in the material and thus the superconductive properties will work to keep the magnetic field unchanging. As with all experiments on the leading edge of the superconductive field, success is limited and not thoroughly understood -- scientists have only been able to produce four samples which exhibit this property (Fitzgerald). CERAMICS In January of 1986, two scientists at IBM's Zurich Research Center developed a new class of ceramic compounds which would become superconductive at a much higher temperature -- high enough to cool with liquid Nitrogen (see Fig. 3). Liquid Nitrogen is extremely cheap and easier to maintain as it boils into gas at a much slower rate (Graham 18). The whole process of cooling with Nitrogen, considering all the technology and materials, is about 1000 times cheaper than Helium -- Nitrogen is cheaper than beer and can be kept overnight in a picnic cooler (Schedter 76).
4 In 1988, Dr. C. W. Chu of the University of Houston discovered a new, cheaper class of ceramic compounds that produced results at 110 degrees Kelvin. Scientists are predicting and desperately looking for a material that will exhibit superconductive properties at room temperature (295 degrees Kelvin) (Graham 18). Some have reported that they have created materials which do so briefly and unpredictably (as long as 3 hours). Many feel that room temperature superconductivity can be achieved reliably in two to four years ("Getting" 42 - 43). One major obstacle which they have to overcome is electron current capability. Present high temperature superconductors are only capable of small currents -- about 1000 times lower than what is desired ("Seeking" 67). APPLICATIONS The desperate chase for high temperature superconductivity is due to the remarkable possible applications. Supercollider technology could benefit as it uses many powerful magnets -- superconductors generate magnetic fields much more efficiently than current technology. These magnetic fields could also be used to contain the reaction in a fusion generator at a cost that would be many times cheaper than that which current experimental fusion reactors experience (Graham 16 - 17). Medical image scanning, which use the penetrating power of magnetic fields over the older technology of x-rays, would
5 also benefit in costs with the switch from Helium to Nitrogen ("Getting" 42). Using room temperature superconduction, power lost in transmission lines could be reduced by 20%. Computers would no longer require bulky fans as their smaller, zero resistance chips would not heat up. This would also mean that they would be faster and use a minimal of power; all this would lead to a very small, fast computer that uses little power (Graham 19 - 20). Because of this zero resistance in superconducting wires, all electric motors could be improved in efficiency (Graham 16 - 17). Communications using electromagnetic waves would get a boost as a high temperature superconductivity coating on the inside of resonators, high-frequency generators, surveillance satellites, television, lasers, particle accelerators, and radio astronomy products improves performance by reducing power loss. This power loss is inhibitive at higher frequencies, but now, using superconductivity, the "wireless" transmission bandwidth increases 167 times as operating frequencies will eventually move from 30 GHz to five TeraHz (5000 GHz) (Cambridge 44 - 45). Electric generators, made more efficient by using superconducting wires, could store their energy in superconducting coils during the night to be used in peak hours during the day. These storage coils would have a
6 current flow without any resistance or voltage source -- energy that can be stored and tapped anytime, forever. V = I * R = 0 (Ohm's Law) where the voltage V is zero, the resistance R is zero, and the current I is limited by the properties of the material. These storage coils could be used in electric autos, thus freeing us from the costs and hazards of petroleum energy ("Seeking" 66 - 67). Deserts might be covered with huge solar collectors which feed these coils (Schedter 74). The Meissner effect could be used to levitate trains over their tracks allowing them to reach speeds of 300 mph. In the 21st century, this principle could also be applied to cars for those who commute frequently ("Getting" 42). Heavy objects could be more efficiently moved down assembly lines in factories using superconducting levitation ("Seeking" 66 - 67). Frictionless bearings could also be a result of the newly discovered effect which "holds" a magnetic field (Fitzgerald). Defense applications are also abundant. Superconducting sensors in the cold of space could be used to detect missile launches. Submarines could be tracked using tiny magnetic detectors scattered throughout the seas. And to counter acoustical detection, a submarine could propel itself through the water with no moving parts using superconductivity to generate magnetic fields which would force water through a pipe ("Seeking" 66 - 67). Strategic Defense Initiative laser technology could get its required
7 megawatt energy burst from superconduction storage units instead of proposed nuclear detonations (Graham 16-17). The benefits of the applications of high temperature superconductivity are enormous -- and extremely profitable to the scientists who develop this new technology. Thus, we will probably see breakthroughs in the near future as scientists put all of their efforts into research. Until then, we can only imagine the possibilities.
Works Cited Cambridge Report on Superconductivity, The. "MIT Finds New Use for Superconductivity." High Technology Business. ________________________ Vol. 8, pp. 44 - 45, August 1988. Fitzgerald, Karen. "Ceramic Superconductors Defy Gravity Anew." Electrical Engineering 443 Course Handout, Fall, 1988. "Getting Warmer . . . ." Newsweek. Vol. 110, pp 42-3, ________ 6 July 1987. Graham, Charles. "Superconductor Speed-Up." Electronics ___________ Handbook. Pp. 16 - 22, 93, Fall 1988. ________ Schedter, Bruce. "How to make your own superconductors." Omni. Vol. 10, pp 72-4+, November 1987. ____ "Seeking the Perfect Wire." U.S. News & World Report. ________________________ Vol. 102, pp 66 - 71, 11 May 1987.