PhD experimentation provides many (many!) challenges, which I’m currently experiencing first hand. My PhD aim is to understand an experiment that is used when characterising materials. It can be compared to a fuse wire. Fuses go from being nice and conductive to melting and the whole circuit breaking. I am not measuring fuse wire but a Superconducting wire. So rather than the piddly 13 amps of current that could knock out your computers fuse it is nearer 1300 amps (field and temperature dependent).
To make things a little more complicated, I am measuring this wire in a magnet field. This magnet works at low temperatures (-269 °C) and it only has a bore (the hole in the middle) that is 4 cm wide.
We aim to measure as much as wire as possible in the magnetic fields and see how the behaviour changes – from being superconductive to not – as we change the way we wind this wire inside the magnet. These different experimental set-ups were simulated and after some number crunching we were confident an effect should be seen. In April, I had an idea of what the experimental results should be. It was then time to get into the lab to find out…
With the experimental constraints: the magnet bore, fitting the superconductor wire in without blocking the hole; the effect of temperature, I build my experiment at room temperature and then cool it 300 degrees; and the huge amount of current I need to put in to the superconducting wire I designed a probe. Essentially a long, narrow metal stick made with lots of copper.
This probe worked fine, for a while…
But I saw in the data the effect of temperature, some components shrunk more than others and the thing became a little loose. We tightened it as much as we could but this resulted in the probe breaking. It was a case of back to the drawing board!
Over the next month I set about redesigned the probe. Mark II was stronger, smaller, with more material to carry the currents needed to make the superconductor not conductive. This design was then refined and tested (and tested!) until eventually I got the probe working and took lots of useful data. I had all the experimental data I needed to make a comparison with my simulations. Job done, for now…
Reflecting on this episode I realise my simulations inputs were not good enough and, in future, I’ll have to improve upon my simulation.
Trial, error and lots of patience…..
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- PhD experimentation: Trial, error, and (lots) of patience….. - 11th January 2017