LOL. This has got nothing to do with the function of electron gun. You might as well just take a cup of water or salt water and stick two electrodes into it.
I made a decent sizes HHO generator in a large pickle jar, I captured the gas and put it in a water bottle. Using a spark plug and a flyback driver, I couldn't get it to ignite for some reason. Then I took the cap off and held a flame to it and it made a soft whoosh and I saw a bit of flames. I don't think it was pure enough for a better pop.