Superconducting field inhibits radiation heat transfer?

[Q_Goest]

I'm reviewing a letter regarding the sheilding of an object using a superconducting magnet as is commonly found in MRI machines. The claim is that the magnetic field created by superconducting windings (wire which is carrying a current and thus creating a magnetic field) and wrapped around an object will prevent radiation heat transfer to the object. It actually says the magnetic field will shield the object from electromagnetic energy including thermal energy and infrared radiation. This winding is thus supposed to shield the object from thermal radiation heat transfer from the environment.

What do you think? Is there any reason to believe a strong magnetic field created by superconducting windings should block radiation heat transfer?

 

[willib]

maybe it is not the magnetic field that is insulating the object..
maybe it is the fluid that is super cooling the superconductor..
question , what kind of resistane can be achieved in the superconducting coil?
can you post some specs of this device ..i am very interrested

 

[shyboy]

The only way to prevent radiation heating is to have insulating shields, which should have the same temperature as an object. Normally the supeconducting magnets are cooled by liquid helium. So, if you have an outside walls at the 4.2K, the radiation heat transfer TO the object will be greatly reduced.

It seems that the author of the letter somehow mistake thermal radiation and electromagnetic interference. It is true, that any thick enough metallic layer can provide electromagnetic shielding, and superconductors are kind of perfectEMI shields, though not ideal. But the thermal radiation comes not from outside but from the neighboring surfaces, thus if we surround the object by a high temperature superconductor, we can greatly reduce the interference, but we still have a strong thermal radiation.

Finally, magnetic field has nothing to do with thermal radition, at least on achivable scale.

 

[Q_Goest]

willib

Thanks for the reply, and also apologize for being a bit obtuse here. Unfortunately I'm not at liberty to explain some details.

maybe it is not the magnetic field that is insulating the object..
maybe it is the fluid that is super cooling the superconductor..

The superconducting windings are at a temperature suitable for superconductivity, ie: less than 40 Kelvin. There is a vacuum space and thermal shielding (multi-layer insulation) around these coils to minimize heat transfer from the environment, but there is also an object inside the coils at a temperature equal to the temperature of the windings. Coils like this are typically immersed in liquid helium which acts as a thermal mass so that they stay cold. The helium is recondensed or replaced depending on the technology employed.

what kind of resistane can be achieved in the superconducting coil?

Typical superconducting wires like these handle hundreds of amps with zero resistance. The current is initiated using a power source and a superconducting switch then changes the current source from an external source, and allows the current to come right back to it's starting point all within the magnet so the windings and switch are all superconducting. Since there is no resistance, the current (hundreds of amps) continues to flow essentially forever without additional power.

 

[Q_Goest]

shyboy

magnetic field has nothing to do with thermal radition, at least on achivable scale.

Yes, I'd agree, but because of the source, I had to ask - I wasn't absolutely sure. I can't understand how anyone can suggest that thermal radiation is blocked or even significantly reduced by the magnetic field created but I'm not a real expert at this.

I'd just like to ensure that when I open my big mouth to suggest that this paper is off the wall with it's contention that thermal radiation is somehow blocked or reduced by the magnetic field, I don't find my foot in there!

 

[willib]

Typical superconducting wires like these handle hundreds of amps with zero resistance. The current is initiated using a power source and a superconducting switch then changes the current source from an external source, and allows the current to come right back to it's starting point all within the magnet so the windings and switch are all superconducting. Since there is no resistance, the current (hundreds of amps) continues to flow essentially forever without additional power.

that is sooo cool , literally !