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).

 

[pmacias]

Thank you for your question. I can provide some insight into how a current can be initiated and maintained in a superconductor.

To initiate a current in a superconductor, an external magnetic field can be used to induce a current. This is known as the Meissner effect, where a superconductor will expel any magnetic field from its interior, creating a current loop. This current will continue to flow as long as the external magnetic field is present.

Another method is through the use of a superconducting magnet. By applying a strong magnetic field to the superconductor, a persistent current can be induced and maintained. This is commonly used in applications such as magnetic levitation trains and MRI machines.

In terms of maintaining a current in a closed loop of superconducting material, the key is to maintain the temperature of the material below its critical temperature. As long as the material remains in its superconducting state, the current will continue to flow without any resistance.

As for your question about magnetic induction, it is possible to induce a current in a superconductor through a changing magnetic field, as long as the material is below its critical temperature. However, this current will eventually decay due to the presence of any resistance in the circuit.

Overall, the key to initiating and maintaining a current in a superconductor is to ensure that the material remains in its superconducting state, either through the use of external magnetic fields or by keeping the temperature below its critical point. I hope this helps to clarify the process for you.