Transcript Turbomolecular pump Vahid Bahrami Yekta MBE LAB UVIC

Turbomolecular pump
Vahid Bahrami Yekta
MBE LAB
UVIC
Pressure
1 atmosphere ~ 1 bar ~ 760 mm Hg ~ 760 torr ~ 100,000 Pa
Ion gauges read in mbar i.e. 1x10-10 mbar = 1x10-13 atm.
Lower Pressure
1x10-4 mbar
Rough Vacuum
1x10-8 mbar
High Vacuum
Ultra High Vacuum
Viscous vs. Molecular Flow Regimes
The gas in a vacuum system can be in a viscous state, in a molecular state or in a state
which is intermediate between these two.
When a system is brought from the atmospheric pressure to "high vacuum", the gas in the
system goes through all these states. The mean free path of the gas molecules is very small
at atmospheric pressure so that the flow of the gas is limited by its viscosity.
At low pressures where the mean free path of the molecules is similar to the dimensions of
the vacuum enclosure, the flow of the gas is governed by viscosity as well as by molecular
phenomena; this is the intermediate flow.
At very low pressures where the mean free path is much larger than the dimensions of the
vacuum enclosure, the flow is molecular.
Viscous > 10-4
Molecular < 10-6
NonRotation
blades
Rotation
blades
Inlet
Outlet
As the gas molecules enter through the inlet, the rotor, which has a number of
angled blades, hits the molecules. Thus the mechanical energy of the blades is
transferred to the gas molecules.
With this newly acquired momentum, the gas molecules enter into the gas
transfer holes in the stator. This leads them to the next stage where they again
collide with the rotor surface, and this process is continued, finally leading them
outwards through the exhaust.
Turbo pumps have advantages over diffusion pumps:
-no back-stream oil into the vacuum system at any time
-can be started and stopped in a few minuets
- can be directly connected to the chamber without a high vacuum
valve.
Turbomolecular Pumps
Potential Problems
– Very high speed rotor blades have close-mating stator blades.
• Slight imbalances can cause vibration and bearing wear
problems.
• Sudden blast of atmospheric pressure can bend the blades
down, causing catastrophic failure, “crashing the pump.”
– Lubrication of the high speed rotor is an engineering problem.
• Circulating oil is most reliable, but pump must be right-side-up.
• Grease-lubricated bearings are less reliable, but allow pump to
be placed at any orientation.
– Too high of a pressure will cause aerodynamic lift and drag.
• Aerodynamic lift can bend blades, causing catastrophic failure.
TURBOVAC MAG line
• Turbomolecular pumps with magnetic rotor
suspension
Thanx