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Free electron beam inducing an EM field in a target?

  1. Aug 7, 2014 #1
    Consider the following experimental setup: the front half of a klystron tube (the electron gun and resonent cavity) or perhaps a free electron laser, several different targets consisting of a highly conductive(metal) object, a possibly conductive object(salt or clay), and a non-conductive object(silica), both in air and under a few feet underground(rock or dirt), as well as a reciever antenna.

    If I tuned this electron beam to an equavelent frequency somewhere between 200 and 1000MHz, how would each target instance respond? Would an EM field of the same or similar frequency as the electron groupings be induced such that the recieving antenna could pick up the signal?
  2. jcsd
  3. Aug 8, 2014 #2
    Basically what I'm asking is if free electrons cause a target material to generate a magnetic field and that if the electrons arrived in pulses, would the strength of the field fluctuate similarly.
  4. Aug 8, 2014 #3


    Staff: Mentor

    Yes. The free electrons would induce time varying electric and magnetic fields in the materials. In the conductive materials those fields would result in some currents which would also produce their own fields.
  5. Aug 9, 2014 #4
    Many mechanisms can induce an electromagnetic field in materials. Which ones are the most relevant depends on the electron energy. You should say what energy you have in mind.
    The response frequency of the material will certainly be the same as the pulse of your beam but this can be masked by the characteristic time with which the response last, if this one is much longer than 1/(pulse frequency). Characteristic times vary widely.
  6. Aug 9, 2014 #5
    Are you saying that I could not only detect the target's presence, but the material it's made of as well?
  7. Aug 9, 2014 #6


    Staff: Mentor

    At least you could detect some of the electromagnetic properties of the target material.
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