Superconductivity for Teachers and High School and Middle School StudentsDeveloped by CEFADr. Tim LynchFunded by: HTS State Outreach Centers: DE-PS36-03GO93001-11: Superconductivity for Teachers and High School and Middle School Students Developed by CEFA Dr. Tim Lynch Funded by: HTS State Outreach Centers: DE-PS36-03GO93001-11 Slide2: Superconductivity is an exciting field of physics! (Picture below is the levitation of a magnet above a cooled superconductor, the Meissner Effect, which will be discussed later.)
Source: University of Oslo, Superconductivity Lab Definition: Definition Superconductivity is the flow of electric current without resistance in certain metals, alloys, and ceramics at temperatures near absolute zero, and in some cases at temperatures hundreds of degrees above absolute zero = -273ºK.
Comparisons of Temperatures: Comparisons of Temperatures Comparisons of Temperatures: Comparisons of Temperatures Formulas for Temperatures:: Formulas for Temperatures: Degrees Fahrenheit = (9/5 * Celsius) + 32
Degrees Celsius = 5/9(Degrees Fahrenheit - 32)
Degrees Kelvin = Degrees Celsius + 273
Discoverer of Superconductivity: Discoverer of Superconductivity Superconductivity was first discovered in 1911 by the Dutch physicist,Heike Kammerlingh Onnes. Source: Nobel Foundation The Discovery: The Discovery Onnes, felt that a cold wire's resistance would dissipate. This suggested that there would be a steady decrease in electrical resistance, allowing for better conduction of electricity.
At some very low temperature point, scientists felt that there would be a leveling off as the resistance reached some ill-defined minimum value allowing the current to flow with little or no resistance.
Onnes passed a current through a very pure mercury wire and measured its resistance as he steadily lowered the temperature. Much to his surprise there was no resistance at 4.2K.
At 4.2K, the Electrical Resistance (opposition of a material to the flow of electrical current through it)Vanished, Meaning Extremely Good Conduction of Electricity-Superconductivity: At 4.2K, the Electrical Resistance (opposition of a material to the flow of electrical current through it)Vanished, Meaning Extremely Good Conduction of Electricity-Superconductivity Source: A Teacher's Guide to Superconductivity for High School Students Superconductivity Today in 2004: Superconductivity Today in 2004 Today however, superconductivity is being applied to many diverse areas such as: medicine, theoretical and experimental science, the military, transportation, power production, electronics, as well as many other areas.
The Science of Superconductivity: The Science of Superconductivity Superconductors have the ability to conduct electricity without the loss of energy. When current flows in an ordinary conductor, for example copper wire, some energy is lost.
The Science of Superconductivity, cont.: The Science of Superconductivity, cont. The behavior of electrons inside a superconductor is vastly different.
The impurities and lattice framework are still there, but the movement of the superconducting electrons through the obstacle course is quite different.
As the superconducting electrons travel through the conductor they pass unobstructed through the complex lattice.
Because they bump into nothing and create no friction they can transmit electricity with no appreciable loss in the current and no loss of energy.
The Science….: The Science…. The understanding of superconductivity was advanced in 1957 by three American physicists-John Bardeen, Leon Cooper, and John Schrieffer, through their Theories of Superconductivity, know as the BCS Theory.
Pictures of Bardeen, Cooper, and Schrieffer, respectively.
The BCS theory explains superconductivity at temperatures close to absolute zero.
Cooper realized that atomic lattice vibrations were directly responsible for unifying the entire current.
They forced the electrons to pair up into teams that could pass all of the obstacles which caused resistance in the conductor.
The Science….: The Science…. The BCS theory successfully shows that electrons can be attracted to one another through interactions with the crystalline lattice. This occurs despite the fact that electrons have the same charge.
When the atoms of the lattice oscillate as positive and negative regions, the electron pair is alternatively pulled together and pushed apart without a collision.
The electron pairing is favorable because it has the effect of putting the material into a lower energy state.
When electrons are linked together in pairs, they move through the superconductor in an orderly fashion.
The Science….: The Science…. One can imagine a metal as a lattice of positive ions, which can move as if attached by stiff springs. Single electrons moving through the lattice constitute an electric current.
Normally, the electrons repel each other and are scattered by the lattice, creating resistance.
A second electron passing by is attracted toward this positive region and in a superconductor it follows the first electron and they travel bond together through the lattice. In Simpler Terms…: In Simpler Terms… Source: Oxford University When atoms join to form a solid, they create what is called a lattice. A lattice is like a jungle gym that links all of the atoms together. Electricity can move through a lattice by using the outer parts of the atoms ‑ the electrons. But imagine the jungle gym is shaking. This would make it very difficult for a person to climb through it. Especially if he's in a hurry. So, it is with electrons. They are constantly colliding with vibrating atoms because of the heat within the lattice.
To solve this problem, let's imagine you are trying to get through a crowd of dancing people. The only way you can do this quickly would be to convince the person ahead of you to lift you up and then, as the next person sees what's happening, the crowd lets you body‑surf across the top of them. This is similar to what happens when 2 electrons team up
Slide17: The first electron convinces the next atom that you deserve special treatment. Once the process starts, everyone joins in and you begin moving forward effortlessly. The person‑to‑person exchange represents the 2 electrons. And, your body represents the electrical charge.
There is, however, one small catch. Since the crowd is so active, you must first slow down the dancing so they can grab you as you arrive overhead. This is done by cooling the atoms to very low temperatures. The fast dance now becomes a slow dance. So our chances are much better to get a free ride across the room. This is superconductivity. In Simpler Terms Continued… Cooper Pair:: Cooper Pair: Two electrons that appear to "team up" in accordance with theory - BCS or other - despite the fact that they both have a negative charge and normally repel each other. Below the superconducting transition temperature, paired electrons form a condensate - a macroscopically occupied single quantum state - which flows without resistance
Animation of Cooper pairs:: Animation of Cooper pairs: The Science….: The Science…. An electrical current in a wire creates a magnetic field around the wire.
The strength of the magnetic field increases as the current in the wire increases.
Because superconductors are able to carry large currents without loss of energy, they are well suited for making strong electromagnets.
The Science….: The Science…. Soon after Kamerlingh Onnes discovered superconductivity, scientists began dreaming up practical applications for this strange new phenomenon.
Powerful new superconducting magnets could be made much smaller than a resistive magnet,because the windings could carry large currents with no energy loss.
The Science….: The Science…. Generators wound with superconductors could generate the same amount of electricity with smaller equipment and less energy. Once the electricity was generated, it could be distributed through superconducting wires.
Energy could be stored in superconducting coils for long periods of time without significant loss.
The Science….: The Science…. The superconducting state is defined by three very important factors: critical temperature (Tc), critical field (Hc), and critical current density (Jc). Each of these parameters is very dependant on the other two properties present
critical temperature (T ) The highest temperature at which superconductivity occurs in a material. Below this transition temperature T the resistivity of the material is equal to zero.
critical magnetic field (Hc ) Above this value of an externally applied magnetic field a superconductor becomes nonsuperconducting
critical current density (Jc) The maximum value of electrical current per unit of cross-sectional area that a superconductor can carry without resistance.
Classroom Demonstration #1: Classroom Demonstration #1 The Meissner Effect
Levitation of a magnet above a cooled superconductor, the Meissner Effect, has been well known for many years. If a superconductor is cooled below its critical temperature while in a magnetic field, the magnetic field surrounds but does not penetrate the superconductor. The magnet induces current in the superconductor which creates a counter-magnetic force that causes the two materials to repel. This can be seen as the magnet is levitated above the superconductor. Demonstration of the Meissner Effect: Demonstration of the Meissner Effect
Source: University of Oslo Materials Needed: Materials Needed Materials:
neodymium-iron-boron (or other strong) magnet
dewar (holds liquid air or helium for scientific experiments)
Procedure: Procedure Carefully fill the styrofoam cup with liquid nitrogen. (This will help to keep the liquid nitrogen in the petri dish from boiling away too fast).
Place the petri dish on top of the styrofoam cup and carefully pour in enough liquid nitrogen until the liquid is about a quarter inch deep. The liquid will boil rapidly for a short time. Wait until the boiling subsides.
Using non-metallic tweezers, carefully place the superconducting disk in the liquid nitrogen in the petri dish. Wait until the boiling subsides.
Using non-metallic tweezers, carefully place a small magnet about 2 mm above the center of the oxide pellet. Upon releasing the magnet it should be levitated approximately 3 mm above the pellet.
Procedure: Procedure The magnet should remain suspended until the superconducting pellet warms to above its critical temperature, at which time it will no longer be levitated. It may either settle to the pellets surface or "jump" away from the pellet.
This demonstration can also be done by placing the magnet on top of the superconducting pellet before it is cooled in the liquid nitrogen. The magnet will levitate when the temperature of the superconductor falls below the critical temperature (T ).
Another interesting phenomenon can be observed, while the magnet is suspended above the superconducting pellet, by gently rotating the magnet. The rotating magnet acts like a frictionless bearing as it is suspended in the air.
Source: A Teacher's Guide to Superconductivity for High School Students
Classroom Demonstration #2: Classroom Demonstration #2 A Superconductive Switch
When a superconductor is in the normal state, the resistance to the flow of current is quite high compared to the superconducting state. Because of this, a simple resistance switch can be easily demonstrated.
Materials Needed: Materials Needed YBCO superconductive wire with attached leads
2 Size C batteries with holder
3 volt flash light bulb with holder
Procedure: Procedure Connect superconductor, light bulb and batteries.
When the superconductor is at room temperature it is in the normal state and will have high resistance.The bulb will not light.
Place the superconductor into the liquid nitrogen. The bulb will light as the resistance decreases.
Remove the superconductor from the liquid nitrogen. The bulb will begin dim and eventually go out as the resistance increases.
Source: A Teacher's Guide to Superconductivity for High School Students Diagram: Diagram Source: A Teacher's Guide to Superconductivity for High School Students The Science Becoming Reality: The Science Becoming Reality Current Applications of Superconductors: Current Applications of Superconductors magnetic shielding devices
medical imaging systems, e.g. MRI’s
superconducting quantum interference devices (SQUIDS) used to detect extremely small changes in magnetic fields, electric currents, and voltages.
analog signal processing devices
microwave devices SQUIDS: SQUIDS Source: Superconductors.org Flux-Pinning:: Flux-Pinning: The phenomenon where a magnet's lines of force (called flux) become trapped or "pinned" inside a superconducting material. This pinning binds the superconductor to the magnet at a fixed distance.
Picture of Flux-Pinning:: Picture of Flux-Pinning: Source: Superconductors.org Emerging Applications: Emerging Applications power transmission
superconducting magnets in generators
energy storage devices
levitated vehicle transportation
magnetic separators How the Science Helps Us: How the Science Helps Us What Types of Superconducting Power Systems Equipment Can Help Us?: What Types of Superconducting Power Systems Equipment Can Help Us? Underground transmission cables
Fault current limiters
SMES, Generators, etc.
Cable – transmits 3 to 5 times more energy than copper wire: Cable – transmits 3 to 5 times more energy than copper wire Source: Southwire Transformer- 2 times overload capacity without insulation damage and environmentally friendly due to lack of oil used in operation.: Transformer- 2 times overload capacity without insulation damage and environmentally friendly due to lack of oil used in operation. Source: Waukesha Electric Systems HTS Motor – requires half the space of copper based motors : HTS Motor – requires half the space of copper based motors
Source: Rockwell SMES (Superconducting Magnetic Energy Storage): SMES (Superconducting Magnetic Energy Storage) Source: American Superconductor Projected Estimates of HTS Applications Source:: Projected Estimates of HTS Applications Source: U.S. Dept. of Energy Superconductivity Program Economic Impact of Superconducting Equipment: Economic Impact of Superconducting Equipment Utilities
Higher density transmission uses & higher economic productivity
Reduced environmental impact
More cost effective industrial processes:
Manufacturing & energy production
Electrical storage, transmission and expansion
More cost effective electrical transportation:
High Speed Rail & MAGLEV technologies
Electric car / bus
Forecasted Market Penetration Curves: Forecasted Market Penetration Curves Source: Analysis of Markets and Future Prices for High Temperature Superconductors HTS Wire Cost ($ per meter): HTS Wire Cost ($ per meter) Source:
Analysis of Markets and Future Prices for High Temperature Superconductors Worldwide Market for Superconductivity: Worldwide Market for Superconductivity Source: Connectus, 2003 Another Nobel Prize for Superconductivity Researchers: Another Nobel Prize for Superconductivity Researchers The awards committee honored the trio--Vitaly Ginzburg, Alexei Abrikosov and Anthony Leggett (shown below)--for "decisive contributions concerning two phenomena in quantum physics: superconductivity and superfluidity." Source: Scientific American
Source: Scientific American Superconductor Demonstration Kits: Superconductor Demonstration Kits Edmund Scientific sells superconducting ceramic discs for educational laboratory demonstrations. The kit includes a disk of YBa Cu O , holder, instructions and bibliography. Contact Edmund Scientific, 101 East Gloucester Pike, Barrington,New Jersey 08007; telephone (609) 573-6250.
Sargent-Welch Scientific sells a superconductivity demonstration kit, which includes experiments demonstrating the Meissner effect, zero-resistance and quantum mechanical effects, and the variables of T , J , and H . Contact Sargent-Welch Scientific Company, 7300 N Linden Ave., Skokie Illinois 67007; telephone (800) SARGENT.
Colorado Superconductor, Inc. sells several superconducting kits which demonstrate the Meissner effect, as well as measurement of T , H , and current density. Contact Colorado Superconductors Inc. at P.O. Box 8223, Fort Collins, Colorado 80526; telephone (303) 491-9106.
Futurescience, Inc. sells a variety of superconducting kits for classroom demonstration and student use. Kits fit nicely on your bookcase and hold the necessary items. One kit has a videotape with extensive safety content, simple cryogenic demonstrations, and examples of activities that can be performed with other kits. Contact Futurescience, P. O. Box 17179, Colorado Springs, CO, 80935, 303-797-2933, 719-634-0185, Fax 719-633-3438
CeraNova Corporation produces helical coils of YBCO. These coils are useful in laboratory superconductivity demonstrations, especially where high resistances above liquid nitrogen temperatures are needed. Contact CeraNova at 14 Menfi Way, Hopedale, MA 01747; phone or fax (508) 473-3200
Sources : Sources U.S. Department of Energy, Superconductivity for Electric Systems Program
Southwire HTS Cable Development Program U.S. Department of Energy 2003 Annual Superconductivity Peer Review 23-July 2003
5/10 MVA HTS Transformer SPI Project Status Presented by Sam Mehta & Ed Pleva, Waukesha Electric Systems For the DOE Peer Review Washington, DC, July 23, 2003
University of Oslo, Superconductivity Lab
Alfred Nobel Foundation