Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Geezer on 02/10/2010 21:11:42
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Are superconducting magnets permanent magnets, or are they really electromagnets?
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superconducting magnets are electromagnets but provided they are maintained at the correct temperature they behave like permanent magnets in as much as after the current to create the magnetic field has been injected into them it will continue to circulate with no loss of power due to their zero resistance.
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So, in a sense, we could almost say that they are both. [:D]
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I think they could be most correctly classed as electromagnets as they contain no aligned electron spins, the field is generated by the current flowing in the coils any iron etc used in their constrution is only there for support.
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I think you are correct, although, I suppose it depends a bit on the definition. If it's simply a magnet that has no external power source, a superconducting magnet is a permanent magnet, as long as you don't let it warm up too much, which isn't so different from the more traditional permanent magnet except for a slight difference in temperature.
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It depends on your definition of permanent, but for most uses, you'd have to continue pumping in energy to cool it, so without external energy, it would stop superconducting.
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In deep space, a superconducting magnet is permanent, providing it is protected from heating above the transition temperature of the particular material. If you used the modern materials that work in liquid nitrogen then all you would need is a simple sunshade or a few layers of reflective insulation to keep it so. Would be a good energy store out in the asteroid belt.
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Of course the holy grail is to find a material that can act like a super conductor at higher temperatures and progress is being made in that field so it may have more common applications than we think.
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I think a superconducting magnet is nothing else than a device able to produce high fields because of high currents; If you switch off the current, you switch off the magnetic field, so it cannot be a permanent magnet, just for this reason. The material is, for example, Niobium-Titanium or Niobium-Tin alloys, which are just conductors.
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I think it's reasonable to say a permanent magnet is a magnet that does not consume electric power to maintain the magnetic field, as that is what distinguishes it from an electromagnet. Therefore, a superconducting magnet is a permanent magnet as it does not consume electric power to maintain the magnetic field.
The temperature aspect is a "bum steer", because traditional permanent magnets also depend on temperature to maintain their field.
Anyway, that's my "theory" and I'm sticking to it (until my field collapses) [;D]
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This video explains a bit of what Geezer is saying
http://nextbigfuture.com/2009/10/magnifye-powerful-17-tesla.html
Of course the holy grail is to find a material that can act like a super conductor at higher temperatures and progress is being made in that field so it may have more common applications than we think.
Searching I tripped over a hot item
http://en.wikipedia.org/wiki/Yttrium_barium_copper_oxide