By Elliot Aniekwilo

Word Count – 1241 (excluding bibliography) with 1370

What are superconductors?

Superconductors are materials that are able to carry electrical current without any electrical resistance but only below a certain temperature (called the critical temperature) and are also capable of repelling magnetic fields. 

In normal (conductive) materials, atoms vibrate causing any electrons moving through them to collide with them and ultimately slow down as a result. However in Superconductors, the metal atoms vibrate much less due to the extremely low temperatures. So, as an electron passes through the metal, it causes the atoms to move closer to the electron, creating an area of positive charge that attracts a further electron – this allows for the creation of cooper pairs/BCS pairs (coined by the Physicists, Leon Cooper, John Bardeen and Robert Shrieffer).These pairs of electrons can only take in energy at certain intervals meaning only particles with an exact amount of energy can interact with cooper pairs. So below the critical temperature of the material, the atoms in them don’t have the right amount of energy to interact with the cooper pairs and therefore the pairs move along the material (not interacting with it) so there is no resistance.

They are also able to expel magnetic fields (as per the findings of physicists Robert Ochsenfeld and Karl Meissner) due to something called the Meissner Effect.The Meissner Effect is when a superconductor is placed in a magnetic field, it produces currents inside the superconductor that creates an opposing magnetic field that cancels out the effect of the original magnetic field stopping it from affecting the material. This is why superconductors are often said to be diamagnetic. It’s also why if you searched up pictures of superconductors, a lot of what you’d see would be levitating materials. Magnets can levitate over superconductors due to the Meissner Effect. When the magnet is introduced, its magnetic field bends around the superconductor causing there to be a force that propels/levitates it upwards.

Superconductors in Engineering

MRI Machines

There is a superconductive magnet made with coils of wire (that consists of superconductive material) in MRI machines. It’s there because passing electricity through it creates an extremely powerful magnetic field and due to the lack of resistance in the wires the large energy required to do this can be maintained. As we know, superconductors can only work in very low temperatures so how are these low temperatures acquired in MRI machines? The wires in the machine are continuously submerged in liquid helium keeping them cold enough to keep resistance at 0 ohms. To keep the extreme cold inside the area – in other words, to insulate it – it’s kept inside a vacuum so that it can’t escape. Overall, although using superconductors here is very expensive, the benefit of gaining a stronger magnetic field and therefore higher quality images of patients outweigh the cost. 

Superfast trains 

As an overview, superconductors can be used in trains to make them levitate and achieve extremely high speeds due to this. The technology is relatively new yet has already been implemented in trains such as the fastest train in the world, the Maglev train, invented by James Powell and Gordon Danby. For this section of the article, I will explain how the Maglev train works and this can be applied to most other superfast trains that use superconductors. 

In order to levitate these trains, strong electromagnets are required. Similar to the MRI machine, this is because powerful magnetic fields are required to make the train levitate. For normal conducting materials, such powerful magnetic fields can not be created due to a high amount of current causing more resistance and therefore greater heat build up. So, they can’t go beyond a certain amount of current. For superconductors, this issue is rectified. As previously discussed, below a critical temperature there will be no resistance and therefore no energy lost as heat to the surroundings. This means that using an exciting current (which is only required once and doesn’t need to be applied continuously) a superconducting electromagnetic can produce a strong magnetic field with a (technically) eternally circulating dc current. To keep the coils at a low temperature, the same technique as used in the MRI machines (liquid helium) is used. However, the cooling system is more complicated, actually as the liquid helium is reused and outside radiation which can cause heat needs to be prevented. This involves many different components that come together to produce a great feat of cryogenic engineering that I won’t delve into currently. The combination of cooling systems as well as the electromagnets produce a system that is made with 4 electromagnets 2 having the north polarity and 2 having the south. These systems are placed at different points on the train on both sides. 

Interestingly, strong magnetic fields can have hazardous effects on human bodies so magnetic shields are integrated into the trains to protect passengers.

Now that we’ve looked at the systems used in the Maglev, we’ll look over how these systems are actually used to move the train at such great speeds. 

Firstly, allow me to note that the levitation of the train is achieved through an annoyingly complicated amalgamation of physics laws and figure 8 shaped metal coils. However the main point is that when the train is moving at a high enough speed, it can levitate but when it’s not moving, or moving too slow, it can’t levitate. It’s for this reason that these trains do have wheels on the bottom for when the train is slowing down and coming into a station or for when it’s leaving a station and speeding up. When enough speed is gained, the wheels retract. 

Secondly, in order to propel the train forwards, propelling coils are placed in the “rails” of the train network. The magnetic field of these coils interact with the magnetic field of the superconducting coils using the simple positioning of the one coil in relation to the adjacent coil. As the train is pushed forwards, the propelling coils switch polarities quickly as the next coil comes along (so that south pushes south and north pushes north). By “controlling the frequency of this switching, you can control the train’s speed”. 

Finally, the Maglev train needs to stay at the centre of the “rail” which means it needs to be laterally stable (so that it doesn’t hit the side walls of the rail). To do this, the figure 8 shaped coils are actually interconnected beneath the train. When the train is centred, no current flows between the connection of the coils but when the train is slightly off the centre, a current flows in the connection between the coils and due to the previously mentioned complicated physics laws, there is suddenly a horizontal force rather than just the vertical that kept the train levitating. This horizontal force moves the train back to being centred (the current between the coils decreases as the train returns to the centre).

Conclusion

Superconductors represent a very exciting and promising field of engineering in the future as they are integrated into more fresh new technologies, which is why I think it’s important to know about what they are and the impacts they already have on our world and science today. In the future, hopefully there will be superconducting materials that only require room temperatures to work and therefore will not need the terribly expensive cooling system they usually do today, opening up much more opportunity for innovative and creative usage.

Bibliography

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‌Magnetic Resonance Imaging (MRI) Scans. (n.d.). How Do MRI Scans Work? [online] Available at: https://mriscans.weebly.com/how-do-mri-scans-work.html.

Woodford, C. (2008). How Do Superconductors work? [online] Explain That Stuff. Available at: https://www.explainthatstuff.com/superconductors.html.

Boslaugh, S.E. (2016). Maglev train | transportation. In: Encyclopædia Britannica. [online] Available at: https://www.britannica.com/technology/maglev-train.

Whyte, C. (2016). How Maglev Works. [online] Energy.gov. Available at: https://www.energy.gov/articles/how-maglev-works.

www.youtube.com. (n.d.). The Incredible Potential of Superconductors. [online] Available at: The Incredible Potential of Superconductors [Accessed 2 Dec. 2023].

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