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Concept
Helicon (physics)
Summary
In electromagnetism, a helicon is a low-frequency electromagnetic wave that can exist in bounded plasmas in the presence of a magnetic field. The first helicons observed were atmospheric whistlers, but they also exist in solid conductors or any other electromagnetic plasma. The electric field in the waves is dominated by the Hall effect, and is nearly at right angles to the electric current (rather than parallel as it would be without the magnetic field); so that the propagating component of the waves is corkscrew-shaped (helical) – hence the term “helicon,” coined by Aigrain.
Helicons have the special ability to propagate through pure metals, given conditions of low temperature and high magnetic fields. Most electromagnetic waves in a normal conductor are not able to do this, since the high conductivity of metals (due to their free electrons) acts to screen out the electromagnetic field. Indeed, normally an electromagnetic wave would experience a very thin skin depth in a metal: the electric or magnetic fields are quickly reflected upon trying to enter the metal. (Hence the shine of metals.) However, skin depth depends on an inverse proportionality to the square root of angular frequency. Thus a low-frequency electromagnetic wave may be able to overcome the skin depth problem, and thereby propagate throughout the material.
One property of the helicon waves (readily demonstrated by a rudimentary calculation, using only the Hall effect terms and a resistivity term) is that at places where the sample surface runs parallel to the magnetic field, one of the modes contains electric currents that “go to infinity" in the limit of perfect conductivity; so that the Joule heating loss in such surface regions tends to a non-zero limit. The surface mode is especially prevalent in cylindrical samples parallel to the magnetic field, a configuration for which an exact solution has been found for the equations, and which figures importantly in subsequent experiments.
Official source
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