how does a turbomolecular pump work?

A vacuum is a space ideally devoid of matter. An approximation to such a vacuum is a region with a gaseous pressure much less than atmospheric pressure. Turbomolecular pumps are a type of vacuum pumps used to achieve and maintain a high vacuum.
These pumps offer a reliable contamination-free high vacuum environment, working on the principle that gas molecules can be given a momentum in the desired direction by repeated collisions with a moving solid surface. A spinning fan “hits” the gas molecules from the inlet of the pump towards the exhaust, in order to create and maintain the vacuum.

Most turbomolecular pumps employ multiple stages, each consisting of a rapidly rotating rotor blade and a pair of stationary stator blades. The system works like a compressor that injects energy into the gas instead of extracting it. Gas captured by the upper stages is pushed into the lower stages and successively compressed to the level of the fore-vacuum (backing pump) pressure. When the gas molecules pass through the inlet, the rotor blades hits the molecules.
Thus the mechanical energy of the blades is transferred to the gas molecules. With this new momentum gained, the gas molecules enter into the gas transfer holes in the stator. This takes them to the next stage where they collide with the rotor surface again and this process continues, eventually leading them out through the exhaust.

At atmospheric pressure, the mean free path of air is about 70 nm. A turbomolecular pump can work only if those molecules hit by the moving blades reach the stationary blades before colliding with other molecules on their way. To achieve that, the gap between moving blades and stationary blades must be close to or less than the mean free path. From a practical construction standpoint, a feasible gap between the blade sets is on the order of 1 mm, so a turbopump will stall (no net pumping) if exhausted directly to the atmosphere. Since the mean free path is inversely proportional to pressure, a turbopump will pump when the exhaust pressure is less than about 10 Pa (0.10 mbar) where the mean free path is about 0.7 mm.

The turbomolecular pump is a very versatile pump in terms of generated pressure. It can vary from intermediate vacuum (≈10−4 Pa) up to ultra-high vacuum levels (≈10−10 Pa).

Turbopumps require a frequency controller to provide the high rotational speeds demanded by these pumps. Lately these controllers have been integrated onto the pump in the form of onboard controllers, thus reducing rack space requirements.

The most recent developments on turbo pumps also allow smart onboard controllers which control valves and gauges and monitor the operations of automated vacuum systems. LINK TO