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A Determination of Extraordinary Waves By Plasma

  1. Jul 27, 2016 #1
    I have been trying to find a method to predict the polarization effects of a plasma with a B Field on low frequency waves. From Chen's Intro to Plasma Physics and Fitzpatrick's Plasma Physics I understand the development of the dielectric tensor and calculation of dispersion with the B field but I don't see how to use this in calculating the effects on a reflected wave. I am using this in studying the ionospheric effects on VLF waves. Would appreciate any help or direction on this subject. Thanks
     
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  3. Jul 28, 2016 #2

    jambaugh

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    It's been a very long time since I took grad EM and a course on plasma physics but here are my intuition on your question...

    I conceptualize reflection off a conductor in terms of an incident wave inducing a current which in turn induces an inverted wave, canceling forward transmission. Then at a conductor non-conductor boundary there is no normal component of conductivity so only the normal component of the wave is reversed.

    With this in mind, a B field through a plasma will reduce conductivity (or rather admittance in the AC paradigm) orthogonal to the B field. To my thinking this effect would apply only for frequencies significantly lower than the electron gyrofrequency for the given B field strength.

    But where it applies, you should see increased transmission and decreased reflection of em-waves polarized orthogonal to the B field. I'm thinking of the undergrad physics lab with the metal comb used to polarize microwaves. The B field would correspond to the direction of the comb's "teeth" in that this is the direction of higher conductivity.

    That's my qualitative intuition which may be wrong and if not may be at too elementary a level to be of help but I offer it FWIW.
     
  4. Aug 2, 2016 #3

    tech99

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    There is quite a lot of discussion about the ionosphere and its operation at different frequencies in the very old "Radio Engineer's Handbook" by Terman, and a number of references, particularly to papers by Appleton, who studied polarization. At low frequencies, the electron velocity is great, and the particles spiral several times for each RF cycle. The ionosphere acts as a good mirror because the index of refraction departs further from unity at low frequencies and the ray does not penetrate very far.
    In the Northern hemisphere, received waves have right hand elliptical polarization, and the converse in the Southern hemisphere, but I presume these effects to be small at VLF due to the small time for which the ray travels through the ionised medium.
     
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