carrying current from an insulator

Discussion in 'The Projects Forum' started by d.sonali20, Dec 11, 2011.

  1. d.sonali20

    Thread Starter New Member

    May 21, 2011
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    I am working on a project that uses a Faraday cup. Its consists of a metallic cylinder(pipe like) with an electrode at the bottom.The ions enter the cylinder and hit the electrode.The resulting current is carried away from the electrode to an amplifier by a wire .Now.the electrode that i am using is an insulator. So how do i provide the electrical connection.the electrode being an insulator,will it give any charge for the wire to carry
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If it is a Faraday cage, how are ions entering?

    What experiment are you duplicating? Might be able to dig up some information.
     
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
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    The Faraday Cup is a device for measuring ion beam currents; it is not the same as a Faraday Cage.

    http://en.wikipedia.org/wiki/Faraday_cup

    I am at a loss to see how an insulator can work as an electrode though, unless it is only relatively insulating with some ion transport possible, perhaps like the glass electrodes used for pH measurement?

    I suspect that as this is a question of physics rather than electronics, it belongs more in the "Physics" section, but really a forum dealing with physics as the main subject may be a better place to ask this.
     
  4. d.sonali20

    Thread Starter New Member

    May 21, 2011
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  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    As commonly understood, a total insulator cannot be an electrode, although it may insulate one.

    Possibly rapidly moving ions can penetrate a normally insulating material, but this is just a guess.

    This really requires advice from a physicist.
     
  6. jimkeith

    Active Member

    Oct 26, 2011
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    I have seen this when working at a particle accelerator--the output is essentially a ground current from the conductive cylinder--because the current is so low, it can be measured more easily as a voltage developed across stray capacitance to ground via a biased electometer.

    In your case, I believe that the 'electrode' is in reality a 'target' that may be required to minimize damage to the cylinder or perhaps it may be used for some conversion process. As such, no direct connection would be required.

    Note that just because I have happened to see one does not make me a guru, but my thoughts may help steer you in the correct direction.

    http://www.faraday-cup.com/What_is_a_Faraday_Cup.html
     
  7. d.sonali20

    Thread Starter New Member

    May 21, 2011
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    can you please explain more clearly what you mean by the electrode simply acting as a target that minimizes damage to the cup.i am not very good at this stuff..
     
  8. d.sonali20

    Thread Starter New Member

    May 21, 2011
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    and i got this information from a research paper

    "The UV photons now create photo electrons by photoionization and or photodetachment of an electron from a
    neutral/negatively charged species with sufficiently low work
    function (or electron affinity)which may in turn be detected at
    the detector electrode of the Faraday cup as a short charge pulse."

    it doesn't seem like the electrode is just acting as a target here.If the charge pulse is created at the electrode,then it has to be collected at the electrode right?Even if the electrode is in direct contact with the cup,it wont transfer the pulse to the cup will it?because its an insulator.
     
  9. jimkeith

    Active Member

    Oct 26, 2011
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    A high energy particle beam could damage its target, depending upon the material--I read that in one case, the faraday cup was constructed of titanium to make it more robust.

    A glass or ceramic target may help in this regard. It may not be an insulator as it could be doped with impurities to increase conductivity, as in semiconductors.

    Notice my use of 'may' and 'could' --I hope that you find someone that is knowledgeable in particle physics--I, myself, know just enough to be very dangerous.

    Regarding the electrometer figure in a previous post that I grabbed off the internet, I believe that the electrometer should be placed between the cup and the potentiometer voltage source--this enables the voltage source to be grounded so that may have human contact without altering the measurement.
     
    Last edited: Dec 12, 2011
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