In the vacuum electron beam welding machine, the vacuum system also often uses a Roots pump as a booster pump for differential pumping. Roots pump is a double-rotor volumetric molecular aspirator, in addition to the volume effect, the working principle of a molecular aspirator is also applied.

Under high pressure, because the mean free path of the gas is smaller than the gap, the discharged gas will return in large quantities, so the vacuum pump cannot work well. In order to make this vacuum pump work normally, a rotary vane mechanical pump is generally used as the Set up the vacuum pump.

When the pressure at the outlet of the front pump drops to about 100Pa, the roots pump starts to work, and its maximum pumping rate appears at 1.33Pa. At this time, the mean free path of the gas significantly exceeds the width of the gap, which greatly increases the return gas. flow resistance, and its intake pressure is linearly related to the outlet pre-vacuum pressure.

The Roots pump has a high pumping speed in the pressure range of 1.33×10-2~1.33Pa, up to 40000L/S, and can quickly discharge the suddenly released gas. In this pressure range, the pumping speed of the rotary mechanical pump is already very small, and the oil diffusion pump has just started to work, so the two pumps are out of touch in the pumping speed, and a first-stage Roots vacuum pump can be added to it. to solve it, so it is also called a booster pump.