Heating the chamber walls and internal parts while pumping, typically to 120 to 250 °C for 24 to 48 hours in UHV work, so adsorbed water and other gases leave in a day instead of over weeks. A good bake lowers the base pressure by one to three decades once the system cools. Every part has to take the heat: Viton seals are usually limited to about 150 °C, while CF copper seals handle far more.
Wrap the chamber in heater tape and foil, we'll bake out at 150 C for 48 hours, then activate the NEG.
Heat evenly and hunt down cold spots: water leaving the hot walls simply sticks to the coolest flange, so foil every viewport and valve body.
Also heard as
- bake
- bakeout
- baking
Related terms
Wet
Said of a chamber whose walls still hold adsorbed water, so it pumps down slowly and stalls high.
Outgassing
Slow release of gas from the surfaces and bulk of materials inside a vacuum system.
UHV
Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.
CF flange
All-metal flange that seals by biting knife edges into a soft copper gasket, the standard joint for UHV.
NEG
Non-evaporable getter: a porous alloy that pumps active gases once it has been activated by heating in vacuum.