A baffle or reservoir cooled by liquid nitrogen at 77 K, a refrigerator or chilled water, placed between a pump and the chamber or in a foreline. Vapours condense on the cold surfaces, which stops pump oil migrating upward and adds a lot of pumping speed for water. A liquid nitrogen trap has to be kept filled, and when it warms up it releases everything it has collected in one burst.
Fill the cold trap before you open the diff pump valve, and top it up again at lunch.
Let a warming nitrogen trap release its load into the pumps with the chamber valved off; letting it warm into a clean chamber dumps the water and oil straight back in.
Also heard as
- LN2 trap
- trap
- cryotrap
Related terms
Diffusion pump
High vacuum pump with no moving parts that drives gas toward the exhaust with downward jets of hot oil vapour.
Backstream
Of pump oil or vapour, to flow the wrong way, from the pump back toward the chamber.
Burp
Brief, sudden pressure burst in a vacuum system from trapped gas, a warming trap or a moving part.
Cryopump
Capture pump that freezes and adsorbs gas onto surfaces cooled to about 10 to 20 K by a closed-cycle refrigerator.