Superconductors – The Two Steves and Mark

We were really looking forward to this talk as Ram is really interested in superconductors and we had read Stephen Blundell's book on the subject already. In fact we had make the suggestion of having him do a talk on superconductors last year!

Also on the stage were Steve Cowley and Mark Lythgoe. It is always a pleasure to see Mark in action; I really believe that neuroscientists are the most interesting people there are!

It started off with Stephen explaining what a superconductor (SC) is. Basically, it is something that can carry current with no resistance. They were discovered by accident after Onnes managed to liquify helium. He started measuring electrical conductivity of metals at low temperatures, and other scientists predicted what would happen.

Some thought that resistance would increase, some thought it would decrease, some thought it would stay the same, but it turned out that in some materials resistance disappeared! They tried with gold at first, which didn't work, then they thought that it would take a pure metal, so they purified mercury and found that there was no resistance when it was immersed in liquid helium. Then they decided to try it without purifying the mercury and found it also worked, so all the effort that went into purifying the mercury was a waste of time!

They also found that a SC displayed the Meissner effect. I will let Wikipedia explain that one.

Stephan makes a SC sound poetic. He said they have the “pure unbroken beauty of the atom.” Normally electrons are in a chaotic state, but in a SC electrons are paired in what are known as Cooper pairs, and it is because of this that electrons all end up going in the same direction even if they are not near each other.

It seems that experiment is better at finding SCs than studying theory, and there was a big jump in the number of discoveries in the 1980s with the use of copper oxides. Then they found ceramics and finally in the last few years iron based Scs with molecular layers in them have been found.

Mark then spoke of some of the applications. The main one that people think of is the MRI machines that can see inside things (not just bodies, check out the MRI scanner in the Discover Zone!)

The coil in the scanner creates a magnetic field, but that would always need a battery to keep it going. If they can cool the magnetic field then it can be self sustaining. This is where the Scs come in. They are cooled with helium, but if a wire breaks, it gets hot, and some of the helium can boil off, then it gets hotter, and then, Quench! Make sure you look for the venting pipe on the MRI machine before you get inside it!

Having SCs means that there are 80 million scans a year done. Some of them gives us insights into the brain, such as the work done at UCL on taxi drivers hypocampuses getting larger as they learn 'The Knowledge' Full paper here or BBC news report here.

However, the new machine they have that runs at 9.4 tesla has been able to image a mouse's heart actually beating, which can then be slowed down to the speed that a human heart beats so that they can study it better. Through this they have found new drugs for the heart. They can also use MRIs to target drugs to different areas by infusing them with nanomagenetic material which they can then use the MRI to not only see the drug but control its delivery to the right area.

Steve then talked about another application that many people don't think of immediately , the use of SCs in fusion. Without the SCs to keep the plasma in the tokamaks under control, they wouldn't be able to advance fusion power. More on that in another blog post on fusion.

As ever, the intelligence of the audience came across in the excellent questions asked. Some of the interesting things that came up were that all SCs are solids, and that they don't understand yet how the new types work. Scs are most useful in enclosed spaces and that they are not so useful over long distances such as in power lines, as the cost of refrigeration outweighs the savings in transmission of power.

Some of the higher temperature (we haven't yet found room temperature SCs) are harder to form as they are not a ductile. Niobium-tin is ductile, but ceramics aren't, so we need more innovative developments from the material scientists.

For the future Steve would like to see transmission lines to carry energy from solar instalations in sunny areas to other areas, and Stephen would like to see further development of trains using Scs. My favourite, which I think will be Mark's too, will always be the MRI scanners, and I will leave you with this song about them.