Dear Dr. Dan Reed,

here are some good advices provided by Dr. Juan José De Miguel in a previous RG similar question, about which I am in total agreement and which I used when I worked, some year ago, with UHV instruments.

The main problem with going down to UHV is the desorption of the water vapor that sticks to the chamber walls when you open it to the atmosphere. So, there are some tips to to prevent/reduce at maximun the adsorption of water inside your chamber:

- Vent your chamber using N2 instead of air;

- Warm up the chamber a little bit, using the heating tapes or an infrared lamp, prior to venting the chamber. This also helps reduce the adsorption of water;

-Keep your chamber vented as shortly as possible. If you need to work for a while in air before finishing, you may want to close the chamber and start pumping it again, even with mechanical pumps only.

- If it is possible, separate that access stage from the main chamber with a gate valve, and mount an additional pumping stage so that you can evacuate the introduction chamber before communicating it with the main chamber.

Good job and best regards, Pierluigi Traverso

Is it possible to design the join in such a way that you can maintain vacuum in the chambers?

suppose instead of joining the chambers directly you join them through a short connector, which can be separately pumped out, and the opening to the connector from each side can be done while everything is connected and sealed. You attach the connector to couple the chambers, pump it out, then open to the two chambers.

may not be feasible with your experimental arrangement but it would solve the problem.

Hi Dan,

Nitrogen purge is a standard for UHV system. It can help, but it is not enough for 10-10 mBar. As Dr. Traverso said, the main problem is water!

I see only one option (but without guarantee): to put your both vacuum chambers in a glove box and connect them inside in order to avoid water adsorption. But it looks too difficult in comparison with backout.

With N2 purge you can get 10-9 mBar, only, I guess.

Dear Dan Reed ,

The best option is to provide both: 1) a constant flow of an ultrapure (at least 6N) nitrogen (or argon) out of both chambers during all the time they're open, 2) a dedicated glovebox around the system continuously purged with the ultrapure gas. This approach is reported to ensure an ultimate vacuum value below 10^-10 mBar , see https://arxiv.org/ftp/arxiv/papers/1601/1601.05401.pdf p.7 lower part.

Though I believe the glovebox might be not really necessary for your planned vacuum level. But purging with 6N nitrogen or argon and keeping the flow on is a must. This will prevent moisture from entering the chambers.