Superconductors: How to Initiate and Maintain a Current | Explained

[monkeybean]

Hello:

I have been reading up on superconductors and everywhere it mentions that once a current is set up in a superconductor, it persists. I understand this, but no where can I find any information on how in practice a current could initially be "started" in a super conductor and made to continue. If you hook a battery to a superconductor, you will induce a large current for a short time due to the drop across the internal resistance of the battery. Basically a short circuit. However, as the battery is depleted, the current will go to zero once again correct? How can you induce a current on a closed "loop" of superconducting material and keep it going? I'm trying to wrap my head around how they do this in practice. Can you induce a current by magnetic induction with no resistance?

 

[Vanadium 50]

You can induce it with a magnetic field, for example.

 

[imsmooth]

Yes, magnetic induction can do it.

See this

Here, a powerful neodymium magnet creates a current loop in the superconductor. This current loop, in turn, creates an opposite magnetic field that repels the magnet.

 

[f95toli]

The best way of doing this in practice if you are trying to e.g. make a magnet is to simply heat a short piece of the wire that forms the loop using a resitive heater (in practice this means wrapping a few turns of the wire around a resistor). Once that piece is heated above the Tc of the superconductor becomes resistive (and usually with a fairly high resistance) meaning you can hook up a current source to the loop and ramp up the current*. Once you've reached the current you need the heater is turned off and the loop goes into "persistent current mode".

*The loop is of course still shunted by the resistive bit; but since you have a resitive bit in parallell with a superconducting bit, most of the current will flow in the latter).