How to properly bake a ultra high vacuum chamber?

Question

I need to get rid of water excess in my vacuum chamber, and for that there is the procedure of baking. In order to do that there are several things that one needs to consider, the power, heat load, type of heat tape to use etc. Since I've never done this before, I hope that some of you could share their advice on that subject.

Answer 1

The usual procedure involves

1. Careful preparation for ultra high vacuum
   • Do you reach a good high vacuum?
   • Can all the equipment withstand high temperatures over a long period of time? If not you might to cool those parts while heating the rest of the chamber.
   • Try to remove all materials that might have a high outgassing rate, otherwise ultra high vacuum is never achievable.
   • Check for residual gas volumes, e.g. from screw threads.
2. Prepare and bake
   • Wrap heat tape around metallic parts of vessel, try to get good contact and not much overlap. The tape should not reach very high temperatures when used alone.
   • Pump, heat and monitor gas pressure. It should rise a bit, exact numbers depend on the circumstances. Do a smell test, if it smells like burnt plastic you forgot something. Heat for at least 24 hours, even at elevated temperatures this might take a long time. The longest time a colleague used was 2 weeks.

If heating is not going to work alternatively use a sorption pump with either liquid nitrogen or liquid helium.