roughing/foreline speeds

[Dennis P Brown]

For a large chamber that is rather good. As you run it, it should get better. If opening, best to supply dry air to atmosphere, then open.

[Shawn Cochran]

I did clean the 'elephant trunk' and I think tomorrow I will go ahead and re-clean the entire interior again, and see what can be done. Should I run the heater / bake out during the pump down each time?

[JoeBallantyne]

If you open it up to ATM (especially if you don't backfill it with dry nitrogen first) then baking it out will help get the H2O off the walls.

I would bake it out whenever I opened it up to ATM, if I wanted subsequently to get the pressure good and low.

But if once baked out, you never actually open it up to normal air with its heavy load of moisture, then repeatedly baking it out is unnecessary.

Chamber will pump down much faster if you always fill it with dry nitrogen, and never expose it to air.

You should experiment and see what works best for you and your application.

Joe.

[Rich Gorski]

4.4x10-7 Torr is getting into the ultra high vacuum region which is quite good for such a large system. It looks like you will reach the 10-8 level with a few more hours of pumping but certainly more cleaning shouldn't hurt as long as you're using a good solvent such as triclor or alcohol after a detergent cleaning with something like Alconox powder. I have some experience with a much smaller system that needed to get into the 10-9 region for field emission electron source work. Once the system got there it wasn't to hard to get it back there after opening up to atmosphere and without using dry N2. It would require a bake out from time to time depending how long it was up to atmosphere and the humidity level. Also my system only saw very clean items placed inside such as electron gun parts of ceramic and stainless steel. The system was cleaned using Alconox powder (alconox.com) mixed with DI water which is typically used for ultra high vacuum chamber cleaning followed by a DI water rinse and then alcohol on a dust free wipe. If you want to get well into the low 10-8 region or better then bake out will likely be required after opening it up to air. Backfilling with dry N2 will help to reduce the time to get down to those levels.

Where you go from here depends on...

1: Your application
2: What vacuum level do you need
3: How much time do you have to get there after opening it up to ATM such as in a production application
4: What contaminants can you live with
5. If your application requires something inside getting hot then a bakeout of the chamber beforehand will really help to reducing outgassing.

Your system seems to be an overkill for typical fusor work so I'm guessing you have some other application in mind.

Good job getting this large chamber into the lower 10-7 pressure.

Rich G.