Does a DC supplied superconductive coil give off radiation?

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    Coil Dc Radiation
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Discussion Overview

The discussion revolves around whether a DC supplied superconductive coil emits electromagnetic radiation. Participants explore the implications of Maxwell's laws, the nature of electric currents in superconductors versus normal conductors, and the conditions under which radiation occurs.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that a DC current does not radiate, regardless of whether it flows through a superconducting or normal conducting material, citing Gauss's Law and the nature of static fields.
  • Others argue that while an individual electron moving in a circle would radiate, a continuous stream of electrons does not, suggesting that the contributions to the radiation field cancel out in a current loop.
  • One participant questions the definition of DC in the context of cyclotron radiation, noting that cyclotron electrons move in expanding spirals and are not strictly DC.
  • Some participants reference quantum mechanical considerations, suggesting that the localization of charge carriers in a wire affects radiation emission, with one citing a paper that discusses steady currents in a non-relativistic limit.
  • There are discussions about the classical versus quantum mechanical treatment of electrons in motion, with references to the Larmor Equation and the radiation-reaction problem in classical electrodynamics.
  • Several participants express confusion over the implications of DC and the conditions under which radiation occurs, with some suggesting that the notion of continuous charge in a DC current may be problematic.

Areas of Agreement / Disagreement

Participants generally disagree on whether a DC current in a superconductive coil emits radiation, with multiple competing views presented. The discussion remains unresolved, with various interpretations and conditions being explored.

Contextual Notes

Participants note limitations in understanding the implications of classical and quantum mechanics on radiation from DC currents, as well as the need for specific treatments or references to clarify the concepts discussed.

Who May Find This Useful

This discussion may be of interest to those studying electromagnetism, superconductivity, and the quantum mechanics of charged particles, particularly in the context of radiation and current flow.

  • #31
vanhees71 said:
The drift velocity is more around ~1mm/s.
I read that drift velocity in superconductors is about 20 meters per second.
 
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  • #32
No.

For the third time, the A-level answer is radiation is caused by time-varying multipoles and these are zero for DC.
 
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  • #33
@hutchphd I think the cyclotron analogy is not usable here because in a coiled wire with steady current the actual electrons move slowly , very slowly so from the standpoint of a single electron the curled wire seems almost straight at the speed it is going. Much like we don't see and don't feel the curve we are actually making while traveling along a long road even though the Earth is curved and we are traveling along a curved path.

In cyclotrons on the other hand you have a relativistic electron beam being deflected by a perpendicular B field. But I have another example that i myself would like to ask, for steady DC current doesn't it also matter in what type of "conductor" the current is flowing? It seems to me a toroidal plasma does emit cyclotron radiation with a steady current, I suspect this has something to do with the confining fields which are present for a plasma and not present for a solid copper wire with DC.
 

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