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Electron Gun ?

  1. May 22, 2010 #1
    can i use ni-chrome wire , for my heated cathode on my electron gun ,
    using Thermionic emission , or what would be a better filament to use.
     
  2. jcsd
  3. May 23, 2010 #2
  4. May 23, 2010 #3
    sweet thanks for the answer .
     
  5. May 23, 2010 #4

    sophiecentaur

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    You could possibly get the filament from a defunct radio valve / TV tube. Goggles, face mask, gloves and protective clothes are needed and be careful when imploding it - knock the tube neck off rather than breaking the screen end? That would give you a convenient source of the best material for electron emission.
     
  6. May 23, 2010 #5
    Just breaking a neck could be bad--- a 'slug' of air can be injected towards the screen---large and fast enough could shatter the tube--and stir up the phosphor into the air that you will be breathing. It's probably better to break off the tip that was used to seal in the vacuum. At least, that is how I have released the vacuum (not implying that I let the vacuum out!:cool:)

    If you do this to a color TV tube, please recycle the glass face--it contains several pounds of lead.

    Neil
     
  7. May 24, 2010 #6

    sophiecentaur

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    I thoroughly agree with that - I forgot about the details of the process but did mention the facemask!
    At one time, CRTs were re-gunned by 'letting the vacuum out' with your method then sawing off the neck.
     
  8. May 24, 2010 #7
    The electron emission current from a hot filament is called thermionic emission, and is discussed in

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

    See also

    http://www.avs.org/pdf/vossenwinner01.pdf

    It is important to get a filament that has a very high melting point (and low vapor pressure), because the thermionic emission coefficient varies as temperature (kelvin) squared (Richardson's equation). If I were looking for a cheap plentiful thermionic-emission electron source, I would use a 3 to 6-volt flashlight bulb or a 6 volt automotive electric lamp bulb.

    Bob S
     
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