differential pumping

"Differential pumping" means that two chambers connected through an orifice or a fine tube with high evacuation resistance are evacuated by separate pumps. Each chamber reaches the pressure determined by the performance of the pumps, without influenced by each other. The camera chamber and the column achieve differential pumping because a fixed aperture (0.5 to 2 mm in diameter) or an orifice is inserted between them. Differential pumping is also executed between the specimen chamber and the electron gun chamber.