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Need some help with Magnetron concepts

  1. May 6, 2009 #1
    I'm writing a paper on the magnetron, and was wondering if anyone can help me with some conceptual elements of its workings.

    I understand it is a thermionic diode, and that a parallel magnetic field causes emitted electrons to travel in a circular path about the cathode.

    How is it that when the circling electron bunches pass by cavities, microwave EM waves resonate in the cavity?

    Any help is greatly appreciated!
  2. jcsd
  3. May 6, 2009 #2
    Please see my post in another thread. The electrons are accelerated by a negative bias on the thermionic cathode, and they orbit in a circle just inside the vanes of the magnetron cavities. Their frequency of revolution is about 27.992 GHz per Tesla of magnetic field (875 Gauss for a microwave oven), so the magnetic field strength determines the revolution frequency. The magnetron microwave cavities are resonant at the desired frequency, and the magnetic field is set to the proper value so they generate a electromagnetic wave which in turn bunches the electrons, which in turn bunches the electrons more, etc.
  4. May 6, 2009 #3
    Hey Bob,

    I'm gonna thank you for both replies here. :)

    The thing I seem to be missing is how is it that the electron bunches produce EM waves? When and how are photons emitted?

  5. May 7, 2009 #4
    EM waves have both transverse E and transverse H components. A bunched electron beam has a radial E field (from Coulomb charge) and an azimuthal H field (from amp current). So a bunched electron beam can couple to (or from) a bunched electron beam.
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