Can Superconductors Reach Relativistic Speeds and Emit Synchrotron Photons?

[sol47739]

TL;DR

I have some questions about superconductors

How are currents injected into a superconductor? And can you regulate the velocity of the current afterwards? Since the magnetic field can’t penetrate?

What would happen if you tried to make the Cooper pairs approach relativistic speeds? Would the superconductor stop being in its superconducting state? Or would it be possible, and in case it would be possible would the Cooper pairs emit synchrotron photons?

 

[Drakkith]

Since the magnetic field can’t penetrate?

The magnetic field can penetrate a small amount. The depth of penetration is known as the London penetration depth, though it is typically very small, on the order of nanometers. Note that a superconductor is, well, a perfect conductor. It responds very intensely to applied magnetic fields since there is no resistance to rob its charges of energy. This is the very reason it expels a magnetic field in the first place.

How are currents injected into a superconductor?

On way is to use low-voltage DC power supplies to run current through feeder wires that are attached to the superconductor. The feeder wires are very low resistance so that minimal power loss happens. Alternatively, you can energize a superconducting coil with the aforementioned DC supply and then short the two ends of the coil together with a piece superconducting wire, forming a closed, superconducting loop.

I believe you can use induction as well, since the superconductor must respond to a changing magnetic field is some fashion in order to oppose it, but I'm not certain.

What would happen if you tried to make the Cooper pairs approach relativistic speeds? Would the superconductor stop being in its superconducting state? Or would it be possible, and in case it would be possible would the Cooper pairs emit synchrotron photons?

As some point, increasing the current causes the superconductor to lose its superconducting properties due to the magnetic field created by the current. This happens well before the electrons become relativistic.

 

[sol47739]

The magnetic field can penetrate a small amount. The depth of penetration is known as the London penetration depth, though it is typically very small, on the order of nanometers. Note that a superconductor is, well, a perfect conductor. It responds very intensely to applied magnetic fields since there is no resistance to rob its charges of energy. This is the very reason it expels a magnetic field in the first place.On way is to use low-voltage DC power supplies to run current through feeder wires that are attached to the superconductor. The feeder wires are very low resistance so that minimal power loss happens. Alternatively, you can energize a superconducting coil with the aforementioned DC supply and then short the two ends of the coil together with a piece superconducting wire, forming a closed, superconducting loop.

I believe you can use induction as well, since the superconductor must respond to a changing magnetic field is some fashion in order to oppose it, but I'm not certain.As some point, increasing the current causes the superconductor to lose its superconducting properties due to the magnetic field created by the current. This happens well before the electrons become relativistic.

Thanks for answering! So if I understand correctly you can't make a current inside a superconductor go to fast since the magnetic field of the current will destroy the superconducting state?

If you increase the current's velocity in other words accelerate it will the superconductor emit electromagnetic radiation as normal accelerating charges would do? I fell that it won't but I am not sure, why or why not?

Is AC current possible inside a superconductor?

 

[Drakkith]

It's not really about speed or velocity, but about numbers. The electrons in any conductor are constantly moving about in a random, unordered motion. Setting up a voltage merely makes some proportion of them move preferentially in single direction around the circuit. The stronger the voltage, the larger the current, the more electrons are moving in this preferred direction at any given time. The velocity of electrons doesn't change much (note I'm talking about the velocity of individual electrons, not the drift velocity).

My understanding is that something similar happens in a superconductor. You have an unordered motion of electrons or electron-pairs and upon having some electric or magnetic field applied some proportion of these will begin to move in a preferred direction. It's just that once the magnetic field of the current reaches some critical value it 'quenches' the superconductor, destroying the superconducting state.

If you increase the current's velocity in other words accelerate it will the superconductor emit electromagnetic radiation as normal accelerating charges would do? I fell that it won't but I am not sure, why or why not?

As long as the superconductor is in a superconducting state then no radiation can be emitted since this would require that the charges lose energy, which would show up as resistance, of which a superconductor has none while in its superconducting state. There are simply no lower energy states that the charges can move to in order to give up this energy to radiation.

 

[f95toli]

Thanks for answering! So if I understand correctly you can't make a current inside a superconductor go to fast since the magnetic field of the current will destroy the superconducting state?

If you increase the current's velocity in other words accelerate it will the superconductor emit electromagnetic radiation as normal accelerating charges would do? I fell that it won't but I am not sure, why or why not?

Is AC current possible inside a superconductor?

Speed has nothing to do with it. Cooper pairs in regular superconductors do not "travel" any faster than charges in normal metal.
It seems you are under the impression that the transport in superconductors is ballistic but that is not the case. The fact that there is no DC resistance does not mean that Cooper pairs can travel any faster than regular electrons.

Also, the question about injecting currents is a bit vague. If the SC is just part of your circuit you just make contact to it in the same way as any other material.
If you are referring to persistent currents in e.g. superconducting solenoids then this is done by simply turning a short piece of the wire normal using a heater (this is known as a heat switch) ; this makes this piece resistive and you can then inject current into the solenoid. Once the solenoid is up to field (=there is enough current circulating) you can turn off the heater which becomes superconducting and therefore creates a perfect short, meaning the current start circulating only in the solenoid. Once this happens you can disconnect the cables to the solenoid if you want (more often than not they are left connected, they make no difference)

Also, sure AC is not a problem but the superconductor is no longer lossless; at high frequencies (~100s of GHZ) SC can actually be worse conductors than good metals

 

[fluidistic]

More of.a.comment.to Drakkith's first reply. A superconductor is not merely a perfect conductor, no. It is more.than that. A perfect conductor (resistivity equals to 0) would freeze any B field inside of it if the material undergone a transition into that perfect conducting state. It would prevent the field from changing w.r.t. time. A superconductor does not behave this way, a superconductor expells any B field inside of it. A.superconductor is a very strange beast compared to an ordinary conductor, even if said conductor was idealized.

 

[Hornbein]

There are 2.5 types of superconductor. Type I expels all magnetic fields to its surface. Type II is honeycombed with electromagnetic vortices each with one quantum of energy. These tiny votives repel one another so form a regular hexagonal lattice. With Type 1.5 the vortices attract at larger distances and repel when closer. The vortices either form small groups or have a random pattern. With Type I the vortices attract so they merge into one

It is believed that neutron star cores are type 1.5. Some gas giant cores may be superconducting metallic hydrogen.