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A DC supplied superconductive ellipsoid solenoid must emit EM radiation according to Maxwell's law because rotation is acceleration

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    $\begingroup$ Yes because the electrons are moving in circles (a spiral path) and by this are accelerated. $\endgroup$ Apr 24, 2017 at 7:09
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    $\begingroup$ @HolgerFiedler While the electrons are moving in circles their drift velocity is so small that I doubt that any measurable amount of radiation is emitted. $\endgroup$
    – user42076
    Apr 24, 2017 at 9:16
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    $\begingroup$ @HolgerFiedler You should convert your comment into an answer. $\endgroup$
    – Yashas
    Apr 24, 2017 at 13:37
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    $\begingroup$ Does this answer your question? Why does not a steady and divergence-less current distribution radiate? $\endgroup$
    – Jon Custer
    Mar 11, 2020 at 13:25
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    $\begingroup$ OP changed this to superconducting wire. Sneaky! $\endgroup$
    – user137289
    Mar 12, 2020 at 12:05

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Energy can be stored via an electric current sent through a coil of superconducting wire. Once the coil is short-circuited (closed on itself), the current flows almost indefinitely without losses (an experiment has already been done for years for a ring) and produces an "eternal" magnetic field The energy is therefore stored in the coil in magnetic and electrical form and can then be retrieved in a very short time. Just like in an atom, there is also a rotational movement of the electrons, but there is no electromagnetic radiation because of the quantization of the energy ( we can consider a a coil ring as a linearized atom...). so if the system (coil) is used to store energy, there is no loss of energy in any form.

https://en.wikipedia.org/wiki/Superconducting_magnetic_energy_storage

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No, it won't radiate because of curvature. It is like an earlier question about current in a straight wire where electrons are accelerating in the field with a Drude-relaxation time.

But of course even a resistor with unconnected terminals has thermal noise, will be radiating at finite temperatures.

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    $\begingroup$ So what is en.wikipedia.org/wiki/Synchrotron_radiation then? $\endgroup$
    – rghome
    Mar 12, 2020 at 8:06
  • $\begingroup$ @rghome That is radiation from the acceleration (change of direction) in bending magnets, wigglers, etc. A coil is not different from an ordinary wire. But I see that you now changed your question to superconducting wire! So no Drude resistance. Sneaky! $\endgroup$
    – user137289
    Mar 12, 2020 at 12:03
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    $\begingroup$ I'm not the OP by-the-way. The comment was a genuine follow-up question, which I think you answered. $\endgroup$
    – rghome
    Mar 12, 2020 at 18:53
  • $\begingroup$ In the changed question the current is ever increasing with time. This completely changed the character of the question without this being consistently reflected in the body. $\endgroup$
    – my2cts
    Jul 14, 2020 at 7:58
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Although the drift velocity of electrons inside a wire is only about 0.1 mm/s (according to this post there is a net flow of electrons through the wire.

Thats why the statement

A DC supplied electric coil must give off EM radiation according to Maxwell's law because rotation is acceleration

is right. Any accelerated electron emits photons.

This could easily be demonstrated by the following experimental setup. Using a current carrying coil the Ohm resistance and the heat giving to the surrounding are higher compared with the straight wire from this coil.

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