Transcript Superconductivity for High School Teachers

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
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
• 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
Temperatures
F
C
K
water boils
212.0
100.0
373.2
body temp
98.6
37.0
310.2
room temp
77.0
25.0
298.2
water freezes
32.0
0.0
273.2
-37.8
-38.8
234.4
dry ice
-108.4
-78.0
195.2
liquid Oxygen
-297.4
-183.0
90.2
liquid Nitrogen
-320.8
-196.0
77.2
liquid Helium
-452.1
-269.0
4.2
absolute zero
-459.7
-273.2
0.0
mercury freezes
Comparisons of 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
 Superconductivity was first discovered in
1911 by the Dutch physicist,Heike
Kammerlingh Onnes.
Source: Nobel Foundation
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
Source: A Teacher's Guide to Superconductivity for High School Students
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
 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 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 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.
(Source: Nobel
Foundation)
 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
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….
 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…
 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
Source: Oxford University
In Simpler Terms Continued…
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.
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:
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….
 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….
 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 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
 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
Source: University of Oslo
Materials Needed
 Materials:
– superconducting disk
– neodymium-iron-boron (or other strong) magnet
– liquid nitrogen
– dewar (holds liquid air or helium for scientific experiments)
– petri dish
– styrofoam cup
– non-magnetic tweezers
– gloves
Procedure
1.
2.
3.
4.
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
 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
 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
 YBCO superconductive wire with attached
leads
 2 Size C batteries with holder
 3 volt flash light bulb with holder
 liquid nitrogen
 styrofoam cup
Procedure
1.
2.
3.
4.
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
Source: A Teacher's Guide to Superconductivity for High School Students
The Science
Becoming
Reality
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.
 infrared sensors
 analog signal processing devices
 microwave devices
SQUIDS
Source: Superconductors.org
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:
Source: Superconductors.org
Emerging Applications







power transmission
superconducting magnets in generators
energy storage devices
particle accelerators
levitated vehicle transportation
rotating machinery
magnetic separators
How the
Science
Helps Us
What Types of Superconducting
Power Systems Equipment Can
Help Us?
 Underground transmission cables
 Fault current limiters
 Transformers
 Motors
 SMES, Generators, etc.
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.
Source: Waukesha Electric Systems
HTS Motor – requires half the space of
copper based motors
Source: Rockwell
SMES
(Superconducting Magnetic Energy
Storage)
Source: American Superconductor
Projected Estimates of HTS
Applications Source:
U.S. Dept. of Energy Superconductivity Program
Economic Impact of
Superconducting Equipment
• Utilities
• Higher density transmission uses & higher
economic productivity
• Reduced environmental impact
• Industrial
More cost effective industrial processes:
• Manufacturing & energy production
• Electrical storage, transmission and expansion
• Transportation
More cost effective electrical transportation:
• High Speed Rail & MAGLEV technologies
• Electric car / bus
• Ship
Forecasted Market Penetration
Curves
Source: Analysis of Markets and Future Prices for High Temperature
Superconductors
HTS Wire Cost ($ per meter)
Source:
Analysis of Markets and Future Prices for High Temperature Superconductors
Worldwide Market for
Superconductivity
Millions
$7,000
$6,000
$5,000
New Electronics Applications
New Large Scale Applications
Magnetic Resonance Imaging
Reseach & Technological Development
$4,000
$3,000
$2,000
$1,000
$0
1997
2000
2003
Source: Connectus, 2003
2010
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





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
 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