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.