Molecular pumps work by transferring momentum from fast-moving surfaces to gas molecules, effectively pushing them from a high-pressure inlet to a low-pressure exhaust, creating a vacuum.
Molecular pumps, such as turbomolecular pumps, are designed to operate in the high vacuum and ultra-high vacuum ranges. Unlike roughing pumps that trap gas molecules, molecular pumps move molecules in a specific direction.
The Core Mechanism
The primary principle behind a molecular pump, particularly a turbomolecular pump, involves high-speed rotation.
Here's how it works based on the reference:
- Inflow: Gas molecules enter the pump through the inlet port.
- Momentum Transfer: The pump contains rapidly spinning blades (rotors). When gas molecules inflow the pump's inlet port, the rotating blades at high speed give the gas molecules momentum and push them to the lower stage.
- Compression Stages: The pump is designed with multiple stages, each typically consisting of a rotor and a stator (a stationary blade). The rotating blades propel molecules downwards towards the next stage, while the stationary blades redirect the flow and prevent backflow.
- Exhaust: Through these multiple compression stages, the gas molecules are compressed and directed towards the exhaust port, where they are typically removed by a fore vacuum pump (a roughing pump).
This repeated process across many stages effectively creates a pressure difference, moving gas from the high-vacuum inlet to the relatively higher-pressure exhaust.
Key Components
- Rotor Blades: Spin at very high speeds (tens of thousands of RPM).
- Stator Blades: Stationary rings between rotor stages, designed to redirect gas flow and improve compression.
- Motor: Powers the high-speed rotation of the rotor.
- Housing: Encloses the rotor and stator stages.
Why High Speed?
The high speed of the rotor blades is crucial. Gas molecules at room temperature move at speeds comparable to sound. To effectively transfer momentum and direct these fast-moving molecules, the pump's blades must spin at speeds high enough to interact significantly with the gas molecules.
Applications
Molecular pumps are essential in applications requiring high vacuum, such as:
- Semiconductor manufacturing
- Particle accelerators
- Mass spectrometry
- Surface science research
- Electron microscopy
By continuously transferring momentum to gas molecules and directing them out of the vacuum chamber, molecular pumps are able to achieve and maintain very low pressures.
