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Tesla Coils & Vacuum

  1. Oct 2, 2013 #1
    Why does Tesla coil detects vacuum leaks?
  2. jcsd
  3. Oct 2, 2013 #2
    what do you mean by that ? because i' m not sure such a thing even exists.
  4. Oct 2, 2013 #3
    It does, I used it, I just didn't know that's what it was.
    Tesla coil is used to detect leaks in vacuum systems, here's also a reference.

    The reference doesn't answer the important question, which is why does it detect leaks? Is it because it ionizes the air entering the vacuum tube through the hole? if so, why does it only ionize the air leaking inside the vacuum and not the ambient air?

  5. Oct 2, 2013 #4


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    Vacuum Leak Detectors
    Continuous duty
    High-frequency induction, Tesla-type coil, with one end of secondary attached to a metal electrode
    Point of leakage is indicated by a bright spot where discharge enters evacuated glass assembly
    Can be used for exciting Geissler tubes, but intended for intermittent use only, for periods of up to 4 minutes, followed by at least 5 minutes “off” between periods of use. Output is 10,000-50,000 Volts at a frequency of three to four megahertz.

    Last edited by a moderator: May 6, 2017
  6. Oct 3, 2013 #5
    Thanks, but that still doesn't answer.
    Yes, it ionizes the air in the vacuum system which is at lower pressure. I wrote it as well.
    Looking at ionization equations it has nothing to do with pressure, and although the model is a theoretical one, I do believe there's a more grounded explanation rather then "it works, the model is only theoretic". Why does low pressure air is prone to ionization more than the ambient air?
  7. Oct 3, 2013 #6


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    [strike]I'd guess that it's the sharp boundary around a hole (a sharp radius of curvature where potential gradient E is greater) where the air breaks down before does air around a smooth rounded surface.[/strike]

    No, I'm wrong. It's just that the sparks can more readily enter the glass (& ionise the gases) where there's a hole in the seal.
    Last edited: Oct 3, 2013
  8. Oct 3, 2013 #7


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    Staff: Mentor

    404 not found

    Should be: http://www.randombytes.net/leak_checking.html

    Apparently lower case to the right of the single / is demanded.
    Last edited by a moderator: May 6, 2017
  9. Oct 3, 2013 #8


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    It is hard to actually pin-point what the issue is here.

    First of all, you should always provide a reference source. It would have saved someone asking you what you're talking about had you given that source way in the beginning.

    Secondly, I'm a bit confused here, especially after reading your last post. It appears that you don't understand the concept of leak detection in general, rather than a specific issue of leak detection using an instrument that incorporates these Tesla coils. I hate to spend time describing the general concept only to realize that you have a more specific issue on hand.

  10. Oct 6, 2013 #9
    Not quite sure what you mean by "understand the concept of leak detection in general".

    While the device I'm referring to is used to detect leaks in vacuum systems, my question is about the how.
    Tesla coils ionizes the air in the vacuum system alone, not the air under STP (or if you wish, under ambient conditions). Yes, if you put it close enough to the glass it will create an electric arc. However, when it reaches the hole itself, it penetrates through and ionizes the gas inside as well.

    My question is: Why does the pressure (doesn't ionize under 1 atm but does under vacuum) affect the ionization?
    Ionization is usually described by an equation which constitutes the relations between the level of the electron being ionized (n), numbers of protons (Z) and multiplied by the energy of the hydrogen atom (after substitution of the hydrogen values) and looks like this: E=(13.6eV*Z^2)/(n^2)

    Where does pressure come out to play in this model?
    If it has nothing to do, why doesn't the Tesla coil ionizes the ambient air? Why does it only ionize the air under vacuum?

    Hope I'm clear this time, if not, please tell me.

  11. Oct 6, 2013 #10


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    I'm not positive that everything I'm saying is correct, but it seems to be in the correct general direction.

    Essentially you first bring the tesla coil to the glass such that the gasses inside ionize *AND GLOW*. when you near a leak the ionized path provides a path to ground (through the pump or capacitive?) and the spark jumps. Above 10 tor the spark will be quenched since the molecules are packed in, and below 10^-3 tor the path is not robust enough to conduct.

    So it seems the glowing and discharge are pressure dependent. Higher pressure gasses (above 10 tor) lose their energy by bumping into each other rather than by glowing. So it isn't exactly the ionization that is pressure dependent, so much as whether the gas glows and provides a conduction path. I would guess that if you look at the illumination and conduction characteristics of ionized gasses you would find them to be pressure dependent.
  12. Oct 6, 2013 #11
    Thanks a lot!
    I will look for illumination and conductance characteristics to further educate myself.

    Again, thanks!
  13. Oct 6, 2013 #12


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    I am far from an expert in this field --- not even a novice --- I would appreciate hearing what you discover and whether I was on the right path.
  14. Oct 10, 2013 #13
    Well being no expert either, I do think the Townsend discharge and Paschen's law to be an explanation, unless someone know's better.
    There's a relation to pressure and to the breakdown voltage of gasses, which is the voltage in which the pretty electric arc is formed between the two electrodes. That's also probably why you can't work with Tesla Coils near metallic parts.
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