Untitled Essay, Research Paper
INTRODUCTION
We’ve all heard about superconductivity. But, do we all know what it
is? How it works and what are its uses? To start talking about
superconductivity, we must try to understand the how "normal" conductivity
works. This will make it much easier to understand how the "super" part
functions. In the following paragraphs, I will explain how superconductivity
works, some of the current problems and some examples of its uses.CONDUCTIVITY
Conductivity is the ability of a substance to carry electricity. Some
substances like copper, aluminium, silver and gold do it very well. They are
called conductors. Others conduct electricity partially and they are called
semi-conductors. The concept of electric transmission is very simple to
understand. The wire that conducts the electric current is made of atoms
which have equal numbers of protons and electrons making the atoms
electrically neutral. If this balance is disturbed by gain or loss of electrons,
the atoms will become electrically charged and are called ions. Electrons
occupy energy states. Each level requires a certain amount of energy. For an
electron to move to a higher level, it will require the right amount of energy.
Electrons can move between different levels and between different materials
but to do that, they require the right amount of energy and an "empty" slot in
the band they enter. The metallic conductors have a lot of these slots and
this is where the free electrons will head when voltage (energy) is applied. A
simpler way to look at this is to think of atoms aligned in a straight line (wire).
if we add an electron to the first atom of the line, that atom would have an
excess of electrons so it releases an other electron which will go to the
second atom and the process repeats again and again until an electron pops
out from the end of the wire. We can then say that conduction of an electrical
current is simply electrons moving from one empty slot to another in the
atoms’ outer shells.
The problem with these conductors is the fact that they do not let all
the current get through. Whenever an electric current flows, it encounters
some resistance, which changes the electrical energy into heat. This is what
causes the wires to heat. The conductors become themselves like a
resistance but an unwanted one. This explains why only 95% of the power
generated by an AC generator reaches consumers. The rest is converted
into useless heat along the way. The conducting wire is made of vibrating
atoms called lattice. The higher the temperature, the more the lattice shakes
making it harder for the electrons to travel through that wire. It becomes like
a jungle full of obstacles. Some of the electrons will bump with the vibrating
atoms and impurities and fly off in all directions and lose energy in form of
heat. This is known as friction. This is where superconductivity comes into
work. Inside a superconductor, the lattice and the impurities are still there,
but their state is much different from that of an ordinary conductor.SUPERCONDUCTIVITY (Theory / history)
Superconductivity was discovered in 1911 by Heike Kamerlingh
Onnes, a Dutch physicist. It is the ability to conduct electricity without
resistance and without loss. At that time, it took liquid helium to get extremely
low temperatures to make a substance superconduct, around 4 kelvins. That
wasn’t very far from absolute Zero (The theoretical temperature at which the
atoms and molecules of a substance lose all of their frantic heat-dependent
energy and at which all resistance stops short.) Kelvin believed that electrons
travelling in a conductor would come to a complete stop as the temperature
got close to absolute zero. But others were not so sure. Kelvin was wrong.
The colder it gets, the less the lattice shakes, making it easier for electrons
to get through. There’s one theory that explains best what happens in a
superconducting wire: When a conductor is cooled to super low
temperatures, the electrons travelling inside it would join up in some way and
move as a team. The problem with this notion was that electrons carry
negative charges and like charges repel. This repulsion would prevent the
electrons from forming their team. The answer to that was phonons. It is
believed that packets of sound waves (phonons) that are emitted by the
vibrating lattice overcome the electrons natural repulsion making it possible
for them to travel in team. It’s as if they were all holding hands together. If
one of them falls in a hole or bumps into something, the preceding electron
would pull him and the following one would push. There was no chance of
getting lost. Since the lattice was cooled, there was less vibration making it
easier for the paired electrons to go through.NEW MATERIAL
That theory worked well for the conventional, metallic, low-temperature
superconducting materials. But later on, new materials were discovered. It
conducted at temperatures never before dreamed possible. That material
was ceramic. What was believed to be an insulator became a
superconductor. The latest Ceramic material discovered superconducts at
125 Kelvin. This is still far away from room temperature but now, liquid
nitrogen could be used. It is much cheaper than the rare, expensive liquid
Helium. Scientists still don’t know how the new superconductivity works.
Some scientists have suggested that the new ceramics are new kinds of
metals that carry electrical charges, not via electrons, but through other
charged particles.PROBLEMS / SOLUTIONS
Throughout the time, scientists have succeeded in increasing the
transition temperature which is the temperature required by a material to
superconduct. Although they have reached temperatures much higher than
4k, it is still difficult to use superconductors in the industry because it is well
below room temperature. Another problem is the fact that the new ceramic
conductors are too fragile. They cannot be bent, twisted, stretched and
machined. This makes them really useless. Scientists are attempting to find
a solution to that by trying to develop composite wires. This means that the
superconducting material would be covered by a coating of copper. If the
ceramic loses its superconductivity, the copper would take over until the
superconductor bounced back. The old superconductors have no problem
with being flexible but the required very low temperatures remain to be a
problem. One good thing about ceramics is the fact that they generate
extremely high magnetic fields. The old superconductors use to fail under low
magnetic fields but the new ones seem to do well even with extremely high
magnetic field applied on them.POSSIBLE USES
The characteristics of a superconductor (low resistance and strong
magnetic fields) seemed to have many uses. Highly efficient power
generators; superpowerful magnets; computers that process data in a flash;
supersensitive electronic devices for geophysical exploration and military
surveillance; economic energy-storage units; memory devices like
centimetre-long video tapes with super conducting memory loops; high
definition satellite television; highly accurate medical diagnostic equipment;
smaller electric motors for ship propulsion; magnetically levitated trains; more
efficient particle accelerators; fusion reactors that would generate cheap,
clean power; and even electromagnetic launch vehicles and magnetic tunnels
that could accelerate spacecraft to escape velocity.THE MAGNETICALLY LEVITATED TRAIN
In my research, I had the chance to learn how two of these applications
work: the magnetically levitated train and magnetically propelled ships.
First, the magnetically levitated train, a fairly simple but brilliant
concept. That train can reach great speeds since it had no friction with it’s
track. The guideway has thousands of electromagnets for levitation set in the
floor along the way. More electromagnets for propulsion are set on the sides
of the U-shaped track. The superconducting magnets on the train have the
same polarity of the electromagnets of the track, so they push against each
other and make the train float about 4 inches above ground. The interesting
concept comes with propulsion. The operator sends and AC current through
the electromagnets on the sides and can control the speed of the train by
changing the frequency of the pulses. Supposing that the positive peak
reaches the first electromagnet on the side of the track. That magnet will
push the magnet making the train move forward. When the negative peak
reaches that same magnet, the magnet on the train would have moved
forward so it will be pushed by that same magnet on the track and pulled by
the following electromagnet on the track, which now has the positive voltage
across it. So the first would be pushing and the second would be pulling. It
takes some time to clearly understand what is going on but it becomes so
obvious afterwards. It’s as if the train was "surfing" on waves of voltage.THE MAGSHIP
Another interesting application is what is referred to as the magship.
This ship has no engine, no propellers and no rudder. It has a unique power
source which is electromagnetism. The generator on the boat creates a
current which travels from one electrode to another which go underwater on
each side of the ship. This makes the water electrically charged. This only
works in salt water because pure water would not conduct the current. The
magnets which are located on the bottom of the ship would produce a
magnetic field which will push the water away making the ship move forward.
There are a lot of problems related with that. The magnetic field could attract
metallic objects and even other ships causing many accidents.CONCLUSION
As time goes by, transition temperature, critical field (maximum
magnetic field intensity that a superconductor can support before failing),
current capacity and all other problems are improving slowly. But, at least
they show that we are moving in the right direction. A lot of people are getting
interested in that field since it promises a lot for the future.