Dr Andrew Steele’s Superconductors Lecture

At the Royal Institute in London, after a talk on particle physics, Dr Andrew Steele, an experimental physicist, gave a lecture on superconductivity.

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In the early 1900s, physicists began debating what effect cooling might have on the resistance of a material. From laboratory experiments, they knew that the resistance of a material decreased as the temperature the metal was at decreased as well. Experiments began on the metal mercury- the only metal liquid at room temperature. Experimental data proved that when the metal reached a certain temperature it began to ‘super-conduct’- it had no resistance.

The implications of this were enormous- yet perhaps not so exciting as they could have been. When a material has no resistance, power can be transported without any loss of energy as heat. However, the temperature at which this occurred for mercury was -269°C- not extraordinarily useful.

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However, as more research was done, ceramics (copper oxides) were found with much higher transition (superconducting) temperatures. Nowadays, the highest known transition temperature is -140°C. This is important as it is warmer than the boiling point of liquid nitrogen: -196°C, meaning the ceramic can be cooled to superconducting temperatures by cheaply manufactured liquid nitrogen.

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After a brief introduction, Dr Steele showed us a small piece of ceramic cooled by liquid nitrogen which when placed over a powerful magnet, literally levitates. This happens because when the superconductor is brought near the magnet, a current is induced. Due to the fact that it has no resistance, the current can continue to flow unimpeded. Theoretically this current could flow forever were the conductor never to warm up.

Uses

1) MRI Machines.

Due to their low resistance, superconductors can be used to produce very strong magnetic fields. These can prove very useful for seeing inside things using water molecules. This proves very useful as it allows us to see inside a person’s brain without cutting open their head, which can be both messy and potentially dangerous.

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(Courtesy of Mr Reid,  a collection of various objects stuck to  MRI machines: http://www.simplyphysics.com/flying_objects.html)

2) The Large Hadron Collider

The LHC needed incredibly strong magnets to manipulate protons round the circular circuit at CERN. The only way to provide this magnetic force is by using superconducting magnets. The tiny mass and very high speeds of the protons mean that a large force is required to alter their paths.

3) Power Supply

Transferring power in superconducting cables is incredibly cost efficient as there is no energy lost as heat. In Long Island, New York, a power station is providing a local area with superconducting, highly efficient cables. The difficulty in large scale usage is cooling the cables and protecting the ceramic from breaking.

4) Nuclear Fusion

Nuclear reactors can use magnetic fields (induced by superconductors) to confine plasma to a circular region and provide perfect conditions for nuclear fusion. This is very exciting for physicists as it means power could potentially be produced very cheaply and transported with minimal loss of energy. The only thing holding back development of nuclear power is funding. Many people see the word NUCLEAR and run for the hills, when in actual fact the word just means ‘relating to the nuclei of atoms’.

5) Maglev Trains

Maglev derives its name from MAGnetic LEVitation and utilises the effect mentioned earlier. If a superconductor is cooled to a superconducting temperature when in a magnetic field, a current is induced and the magnet ‘memorises’ its position in the field meaning it will not move horizontally or vertically out of the field. This is called flux pinning and currently is being used in Japan.

LINKS:

Dr Steele on Magnetic Levitation: http://www.youtube.com/watch?v=mAkFr8ZYthw

His website: http://andrewsteele.co.uk/

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