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According to my current knowledge, the Cooper-pairs in a closed superconducting circuit should "feel" a centrifugal force. The (-2) charged pairs are therefore accelerated.

Do the Cooper pairs emit photons? Is there some mechanism that prevents it? Even if you look at the complete wavefunction, still there is an electric charge that accelerates. At different points in the circuit, this acceleration is different. I can't find any reason why they shouldn't, but I'm not sure. I'm not sure either if this case the form of the circuit has the same implications as that of a closed circular circuit (apparently not, according to the comments below).

Has the solution to this question has something to do with the Meissner effect, as in the answer below (though I can't see how)?
Or is the emission that small (because of the small acceleration due to the low temperature) that it effectively has no effect on the current's energy? Just stating that the definition of a superconductor is that it experiences no resistance begs the question.

So, Is there anyone who can help me solve this riddle? Much obliged in advance!

Deschele Schilder
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2 Answers2

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Steady currrents do not radiate, as per Maxwell equations. This has nothing to do with superconductivity. As for why the electrons Bremsstrahlung cancels out, see http://kirkmcd.princeton.edu/examples/steadycurrent.pdf .

Andrea Alciato
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  • But this is not a steady current. It's radially accelerated (like a ball on a rope traces out a circular trajectory). – Deschele Schilder Aug 27 '20 at 07:23
  • @descheleschilder, yes, the charges are radially accelerated. But that doesn't mean that the current is not steady. – BowlOfRed Aug 27 '20 at 07:46
  • The argument provided in my reference holds for a closed loop. – Andrea Alciato Aug 27 '20 at 07:49
  • @BowlOfRed Well, that's the question. – Deschele Schilder Aug 27 '20 at 07:57
  • @AndreaAlciato I was always told at school that accelerating electrons (and thus Cooper-pairs) emit radiation, i.e. Brehmsstrahlung. – Deschele Schilder Aug 27 '20 at 08:03
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    @descheleschilder Me too, but I was also taught Maxwell equations. And, for the third time, I provided a reference illustrating how the Bremsstrahlung (one h, not two) cancels. – Andrea Alciato Aug 27 '20 at 08:12
  • @AndreaAlciato What do you mean by one h? One unit of electric charge? The article ain't about superconductive materials. – Deschele Schilder Aug 27 '20 at 09:29
  • @descheleschilder I mean that it is Bremsstrahlung (from bremsen - to brake), not Brehmsstrahlung, as you wrote. As I wrote, the issue has nothing to do with superconductivity. – Andrea Alciato Aug 27 '20 at 09:44
  • The h is the extra h you put in Brem ... . By the way, iI think I am wasting my time. Bye. – Andrea Alciato Aug 27 '20 at 10:00
  • That doesn't my question in the comment. You just point me at mistaken spelling. What stands the "h" for ("one h, not two")? What makes the Strahlung bremm? Bremmstrahlung by definition isn't canceled. The analysis you make a reference to confines itself to non-superconducting material. – Deschele Schilder Aug 27 '20 at 10:01
  • @AndreaAlciato Now that's a platitude! – Deschele Schilder Aug 27 '20 at 10:02
  • I think you don't understand what I'm asking so I'm wasting my time too! Bye-bye! – Deschele Schilder Aug 27 '20 at 10:04
  • @descheleschilder I think you misunderstood Andrea's comments/answer. If you have a circular circuit, then there will be no radiation if you have a steady current, it doesn't matter if you consider superconductivity or regular conductivity.

    Though the question could become interesting if you allow the shape of the circuit to vary!

     – untreated_paramediensis_karnik Aug 27 '20 at 11:39
  • @thermomagneticcondensedboson Has this been experimentally verified? – Deschele Schilder Aug 28 '20 at 04:51
  • "... attempts to set a lower bound on their [persistent currents in superconductors] duration have reached values of over 100,000 years" https://en.wikipedia.org/wiki/Persistent_current#In_superconductors – Andrea Alciato Aug 28 '20 at 09:31
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Superconducting currents do not radiate. If they did, then energy and momentum conservation would lead to a slowing down of the current, but you correctly say that does not occur. As for the mechanism that prevents radiation I suspect it is some variation of the Meissner effect.

Deschele Schilder
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Lewis Miller
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