 Electromagnetic electron wave

An electromagnetic electron wave is a wave in a plasma which has a magnetic field component and in which primarily the electrons oscillate.
In an unmagnetized plasma, an electromagnetic electron wave is simply a light wave modified by the plasma. In a magnetized plasma, there are two modes perpendicular to the field, the O and X modes, and two modes parallel to the field, the R and L waves.
Contents
Cutoff frequency and critical density
In an unmagnetized plasma in the high frequency or low density limit, i.e. for ω > > (4πn_{e}e^{2} / m_{e})^{1 / 2} or , the wave speed is the speed of light in vacuum. As the density increases, the phase velocity increases and the group velocity decreases until the cutoff frequency where the light frequency is equal to the plasma frequency. This density is known as the critical density for the angular frequency ω of that wave and is given by
 .
If the critical density is exceeded, the plasma is called overdense.
In a magnetized plasma, except for the O wave, the cutoff relationships are more complex.
O wave
The O wave is the "ordinary" wave in the sense that its dispersion relation is the same as that in an unmagnetized plasma. It is plane polarized with E_{1}B_{0}. It has a cutoff at the plasma frequency.
X wave
The X wave is the "extraordinary" wave because it has a more complicated dispersion relation. It is partly transverse (with E_{1}B_{0}) and partly longitudinal. As the density is increased, the phase velocity rises from c until the cutoff at ω_{R} is reached. As the density is further increased, the wave is evanescent until the resonance at the upper hybrid frequency ω_{h}. Then it can propagate again until the second cutoff at ω_{L}. The cutoff frequencies are given by
R wave and L wave
The R wave and the L wave are righthand and lefthand circularly polarized, respectively. The R wave has a cutoff at ω_{R} (hence the designation of this frequency) and a resonance at ω_{c}. The L wave has a cutoff at ω_{L} and no resonance. R waves at frequencies below ω_{c}/2 are also known as whistler modes.
Dispersion relations
The dispersion relation can be written as an expression for the frequency (squared), but it is also common to write it as an expression for the index of refraction ck/ω (squared).
Summary of electromagnetic electron waves conditions dispersion relation name light wave O wave X wave (right circ. pol.) R wave (whistler mode) (left circ. pol.) L wave See also
Categories:
Wikimedia Foundation. 2010.