Powerpoint for Super conductivity / fluidity - Angelfire

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Nov 15, 2013 (3 years and 11 months ago)

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Superconductivity and
Superfluidity

John Scognamiglio

and Dan McLaughlin

Superconductivity


What is superconductivity?


Superconductivity is a phenomenon occurring in
certain materials at low temperatures, characterized by
exactly zero electrical resistance and the exclusion of
the interior magnetic field.


Superconductor is an a material that will conduct the
electricity without resistance below what’s called a
critical temperature. Once set in motion, the electrical
current will flow forever in a closed loop of
superconducting material, making what’s virtually a
perpetual motion scenario.

History of Superconductors


In 1911 Heike Onnes of
Leiden University cooled
mercury to the
temperature of liquid
helium (4 degrees
Kelvin). Once this
happened, the resistance
disappeared.

History of Superconductors


In 1933, Walter Meissner and Robert
Oschenfeld discovered that a superconductor
repels magnetic fields. This is the principle upon
which the electric generator operates. But, in a
superconductor the induced currents exactly
mirror the field that would have otherwise
penetrated the superconducting material
-

causing the magnet to be repulsed. This is what’s
called the Meissner Effect.

Meissner Effect


Above the Critical
Transition Temperature
(Tc), the magnetic field
goes through


Below the Tc, the
magnetic field goes
around it

History of Superconductors


In 1957, three American scientists, John Bardeen, Leon Cooper,
and John Schrieffer wrote the BCS Theory. It explained
superconductivity at low temperatures close to absolute zero for
elements and simple alloys. It fails however as temperatures
increase and materials get more complex. BCS suggests that
electrons team up in cooper pairs. Cooper pairs are two electrons
that appear to "team up" in accordance with theory despite the
fact that they both have a negative charge and normally repel
each other. (Named for Leon Cooper.) Below the
superconducting transition temperature, paired electrons form a
condensate which flows without resistance. However, since only
a small fraction of the electrons are paired, the bulk does not
qualify as being a "bose
-
einstein condensate".


http://www.superconductors.org/terms.htm#cooper

History of Superconductors


In 1986, Alex Muller and Georg Bednorz created a
ceramic
-
like material that acted as a superconductor at
30K. This was unprecedented since ceramic is an
insulator, scientists wouldn’t have guessed it to be a
superconductor.


This led to an enormous amount of research in the
field. In January 1987, a group from the University of
Alabama substituted Yttrium of Lanthanum in the
Muller and Bednorz experiment and achieved a Tc of
92K. This was a breakthrough in because it’s the first
time a material has been able to superconduct at a
temperature higher than liquid nitrogen.

History of Superconductors


The world record is held by a thallium
-
doped,
mercuric cuprate comprised of Mercury,
Thallium, Barium, Calcium, Copper, and
Oxygen. The Tc of this is 138K.


(Hg0.8Tl0.2)Ba2Ca2Cu3O8.33

Uses of Superconductors


Magnetic Levitation is currently
one of the best uses for super
conductivity. A train for example
could be made to float on super
conducting magnets, virtually
eliminating the friction. These are
advantageous because they are
smaller than standard magnets, and
electromagnets tend to waste much
of the electricity via heat. The
downfall is that a strong magnetic
field, such as the one needed in a
case like this can create a bio
-
hazard. These trains are called the
MagLev Trains. The first US
MagLev is set to debut this year.


The Yamanashi MLX01
MagLev train.

Uses of Superconductors


Biomagnetism is another field in which superconductors are
being used in. by impinging a strong superconductor
-
derived
magnetic field into the body, hydrogen atoms that exist in the
body’s water and fat molecules are forced to accept energy from
the magnetic field. They then release this energy at a frequency
that can be displayed graphically by a computer.


The Korean superconductivity group has carried biomagnetic
technology a step further with the development of a double
relaxation oscillation superconducting quantum interference
device for use in magnetoencephalography. This device is
capable of sensing a change in a magnetic field over a billion
times weaker than the force that moves the needle on a compass.
Thanks to this, the body can be probed to certain depths without
the need for the strong magnetic field associated with MRI’s.

Uses of Superconductors


The Superconducting Super
-
Collider project
was planned for construction in Ellis county,
Texas before congress cancelled the project. The
concept of such a large, high
-
energy collider
would never have been viable without
superconductors. High
-
energy particle research
hinges on being able to accelerate sub
-
atomic
particles to nearly the speed of light.
Superconductor magnets make this possible.

Uses of Superconductors



Electric generators made with superconducting wire are far
more efficient than conventional generators wound with copper
wire. In fact, their efficiency is above 99% and their size about
half that of conventional generators. These facts make them very
lucrative ventures for power utilities.
General Electric

has
estimated the potential worldwide market for superconducting
generators in the next decade at around $20
-
30 billion dollars.
Late in 2002 GE Power Systems received $12.3 million in
funding from the U.S. Department of Energy to move high
-
temperature superconducting generator technology toward full
commercialization.

Types of Superconductors


Type 1 Superconductors:


comprised mainly of metals and metalloids
that show some conductivity at room
temperature. They require incredible cold to
slow down enough to facilitate unimpeded
electron flow in accordance with what is
known as the BCS theory explained earlier.


Categorized as the soft superconductors.
They require he coldest temperatures to
become superconductive, and the transition
is VERY sharp


Some examples are:


Lead

7.196K


Tin

3.72K


Zinc

0.85K


Titanium

0.40K


Rhodium

0.000325 K

Types of Superconductors


Type 2 Superconductors


comprised of metallic compounds and alloys. They
achieve higher Tc’s than Type 1. There still lays a
mystery behind the reason for this, however.


The highest Tc attained at ambient pressure is 138K


(Hg0.8Tl0.2)Ba2Ca2Cu3O8.33


Categorized as the hard superconductors. Their
transition from a normal to superconducting state is
gradual.


Type 2 allow some penetration by an external magnetic
field into its surface.

Types of Superconductors


Type 2 (Continued)


“The first superconducting Type 2 compound, an alloy of lead
and bismuth, was fabricated in 1930 by W. de Haas and J.
Voogd. But, was not recognized as such until later, after the
Meissner effect
had been discovered. This new category of
superconductors was identified by L.V. Shubnikov at the
Kharkov Institute of Science and Technology in the Ukraine in
1936(1) when he found two distinct critical magnetic fields
(known as Hc1 and Hc2) in PbTl2. The first of the oxide
superconductors was created in 1973 by DuPont researcher Art
Sleight when Ba(Pb,Bi)O3 was found to have a Tc of 13K.”



http://www.superconductors.org/

Recent Events in Superconductivity


14 February 2006


Physicists in Japan have shown that "entirely end
-
bonded" multi
-
walled
carbon nanotubes can superconduct at temperatures as high as 12 K, which is
30 times greater than for single
-
walled carbon nanotubes. The discovery has
been made by a team led by Junji Haruyama of Aoyama Gakuin University in
Kanagawa. The superconducting nanotubes could be used to study
fundamental 1D quantum effects and also find practical applications in
molecular quantum computing (
Phys. Rev. Lett.

96 057001).


Haruyama and colleagues have designed a system in which there is a
superconducting phase that can compete with the TLL phase and even
overcome it
--

a feat hitherto believed impossible.


Carbon Nanotube


rolled up sheets of graphite which have a diameter in the
nanometer range.



http://physicsweb.org/articles/news/10/2/8/1

Recent Events in Superconductivity


China is attempting to build the first “artificial sun”


Jan 21, 2006


A full superconducting experimental Tokamak fusion
device, which aims to generate infinite, clean nuclear
-
fusion
-
based energy, will be built in March or April in
Hefei, capital city of east China`s Anhui Province.


http://www.angolapress
-
angop.ao/noticia
-
e.asp?ID=409853


What is Superfluidity?


What is superfluidity?




Superfluidity is the
phenomenon wherein a
substance undergoes a state
change that completely
removes viscosity


the matter
flows infinitely and without
friction. The lack of friction is
directly related to the infinite
mobility of a superfluid


friction creates heat, and even
slight heat (say from light) can
cause a superfluid to return to
a normal fluid state. The lack
of friction allows the perpetual
motion of the superfluid to
exist and serves as a
“loophole” in
thermodynamics.




“Lisa, in this house, we
obey the laws of
thermodynamics!”



-

Homer Simpson

Superfluidity’s History




Pyotr Leonidovich Kapitsa, John F. Allen, and Don
Misener first discovered superfluids in 1937 after 1908
research noted that, because of its small mass
(4.002602, for those of you without your periodic table
of elements) and weak forces between its atoms, helium
does not enter from its liquid state to its solid state
without high pressure (25 atm). The researchers fooled
with slight modifications in temperature to see its effect
on helium atoms and found a new phase of matter that
they called “superfluid.”

What is Superfluidity?




Whereas superconductivity deals with an
environment wherein electrons can flow without
resistance, superfluids are atoms that can flow without
friction.




Superfluids operate at extremely low temperatures,
just above the range of absolute zero.




This seems to contradict the common conception
that lowering temperature can eventually slow atoms to
a complete stasis and exhibits quantum mechanics on a
macroscopic, fully observable scale.

How does it work?




The most common matter used in superfluid studies is the helium isotope,
helium
-
4. When helium
-
4 is cooled to 5.2º K, it turns into a liquid. Further
cooling doesn’t immediately result in a state change into a solid. Instead, as
long as pressure remains moderate, helium
-
4 becomes a superfluid at 2.17º K.
Being a boson, it adheres to Dose
-
Einstein condensate dynamics in
interacting systems.




Helium
-
3, the only other stable isotope of helium, also becomes a
superfluid at a low enough temperature, 2.6 mK, and is about one millionth as
abundant as helium
-
4.




Bosons are particles with an integer spin; fermions are particles with half
-
integer spins. Only one fermion can occupy a given quantum state whereas
there are no limitations for bosons. The lack of restrictions on bosons gives
way to Bose
-
Einstein condensates.

How does it work?




Bose
-
Einstein condensates are bosons cooled to
temperatures just above absolute zero and are
considered a phase of matter with odd characteristics,
such as a lack of friction and the propensity to mold to
the shape of their container and surround it rather than
fill it, overcoming gravity in the process via quantum
mechanics. Bosons, at a low enough temperature,
occupy their lowest possible energy state, and various
anomalies occur, superfluidity being one of them.

How does it work?




“Because of the
characteristic profile of
the heat capacity curve,
the temperature at which
the transition takes place
is called the lambda
temperature (Tλ).”




(quoted text and diagram from
http://www.yutopian.com/Yuan/TFM.html)

Why Superfluidity is Important




The most common (though “common” is used lightly here) practical
application for superfluids lies in the use of helium
-
3 and helium
-
4 in
cryogenics, most specifically dilution refrigerators. This is because of their
usefulness via mobility at incredibly low temperatures. Also, their low
temperature results in less thermal interference with the natural temperature
of outer space and any machinery out there.




Superfluids can be used in gyroscopes without creating disruptive
vibrations.




Another important aspect of superfluids is that they exhibit quantum
mechanics on a large scale (measurable in centimeters) in terms of boson and
fermion interactions. When placed in a rotating, sealed container, the speeds
at which the superfluids rotate is in a state of quantized vorticity, or exact,
increasing gradations of speed emanating from the center of the rotation.

Strange Phenomenon




For a normal liquid, one can take a container of the
liquid and make it flow outward by using a siphon (i.e. a
hose or tube) whose end is below the source and has an
initial force (suction) acting on it. This is because, in
part, of gravity and pressure working in a roundabout
manner. The liquid will at first go up out of the tube to
reach the final destination below its starting point.
With superfluids, no external force or mechanism is
needed for the matter to flow upwards (coining the
term the “
fountain effect
”) and out of a container.

Experiments! We Are Science!




In 2000, hydrogen was revealed to be a superfluid, but only under specific
circumstances, so exact and unstable that any substantial amount of a hydrogen
superfluid is unattainable at this time. In the experiment, researchers reasoned that
because of Bose
-
Einstein condensation, the expected temperature that hydrogen
would

be a superfluid occurs after the temperature that it becomes a solid. To counter that,
hydrogen droplets were surrounded by larger helium
-
4 droplets (which would cool at
0.38 K), and some had helium
-
3 droplets enveloping the helium
-
4 (which would cool
at 0.15 K).

Experiment! Continued




To test whether it became a superfluid or not, the hydrogen
atom enveloped a linear carbonyl sulphide molecule (OCS).
Also, instead of using hydrogen, they used “parahydrogen,”
which utilizes protons that spin in opposite directions. The
droplets were placed in a vacuum that was measured by an
infrared laser. If hydrogen did act as a superfluid, a substantial
amount of it would break away from the OCS. The experiment
showed some ambiguity as to exactly when hydrogen becomes a
superfluid, but the researchers speculated that it was at 0.15 K
after running a similar experiment with deuterium.

More Experiments




On December 23rd, 2005, a study was published that showed
physicists what they had been wondering for the better half of a
century: superfluidity comes, in part, from the quantum
interaction of equal fermion pairings, but what would happen if
an unequal amount of fermions were in a system? Scientists at
Houston’s Rice University took fermionic lithium
-
6 atoms,
cooled them to 30 billionths of a degree over absolute zero, ad
studied them to observe any quantum pairings, manipulating the
spin of fermions via radio waves. They were able to create an
excess of 10% unpaired fermions without having any deleterious
effect on the superfluid. They successfully created a superfluid
gas.

Reflecting on the Lithium
-
6
Experiment




"The gas behaves as if it is still perfectly paired, which
is quite remarkable given the excess of spin
-
up atoms.
This was unexpected, and it could signal a new, exotic
form of superfluidity that may be akin to the electron
pairings in unconventional superconductors or to the
quark soup that's predicted to exist at the heart of the
densest neutron stars."


Randy Hulet, head of the
experiment.

Hypothetical Superfluids




Astrophysicists hypothesize that
neutron stars (stars created as the
result of certain types of
supernovas and are characterized
by an incredibly high mass density,
a remarkably small size, and a large
rotation speed) contain neutron
and proton superfluids, but
because of the difficulty in directly
observing such phenomenon, this
is speculation.

References


Superconductivity


http://www.physnet.uni
-
hamburg.de/home/vms/reimer/htc/contents.html


http://en.wikipedia.org/wiki/Superconductivity#Theories_of_supercond
uctivity


http://www.superconductors.org/INdex.htm


http://physicsweb.org/articles/news/10/2/8/1


http://www.angolapress
-
angop.ao/noticia
-
e.asp?ID=409853



Superfluidity


http://en.wikipedia.org/wiki/Superfluidity


http://www.fluidmech.net/msc/super/super
-
f.htm


http://physicsweb.org/articles/world/13/11/3


http://www.yutopian.com/Yuan/TFM.html


http://www.sciencedaily.com/releases/2005/12/051223090405.htm


http://irtek.arc.nasa.gov/DR_page/DRuses.html