Reply To: NIMBY FUD

[asymmetric_implosion]

Using cold gas makes the chamber cold so it will be hard to see the gas leak which tends to be very small quantities.

When vendors qualify components, it is common to place a detector on the vacuum side of the system and puff small amounts of helium on the air side. Those of us that are users tend to use the same protocol because you can localize (~4″) the leak as helium moves quickly, easily penetrates the leaks and does not occur in natural air at a reasonable quantity. It is a bit of an art to get started but the key is very low flow rates or small puffs. Don’t start spraying helium everywhere. If you take your time and do it well, a vacuum system like FoFu-1 can be leak checked in ~1 hr. With some practice you can localize a leak to less than 1″. Normally, you can find the leaking spot if you localize the leak to 4″. The common problems are damage to the sealing surface, debris on an o-ring or damage to a knife edge. Debris can be as small as a human hair or as large as finger nail clipping (yeah, I saw it once). Good vacuum practice will eliminate the debris. Damage can be accidental or due to manufacturing problems. Usually you will feel them before you see them. I hope someone has fingernails. Run them over sealing surfaces. You can’t hurt the metal but you will generally feel some damage before you see it.

A trick we use is to pump the system in pieces by using blank flanges to test the chamber separately from the electrode assembly region. I can’t speak for anyone else but I find solving a few little problems better than solving one huge problem.