Ion pumps: their use and operation in ultra-high vacuum
October 13,2020
2 MIN READ
Ion getter pumps, also called sputter ion pumps or simply ion pumps, are highly effective, quiet, and require little maintenance, making this technology an attractive choice for various ultra-high vacuum (UHV) applications.
How do ion pumps operate?
Ion pumps make use of a large magnetic field within an isolated chamber and use high voltages to pull electrons into the assembly. They rely on the sputtering of getter materials located inside a series of cells and through the implantation, or burial, of the ions produced.
During operation, the gas molecules pumped by chemisorption and physisorption become permanently bound and are no longer able to contribute to the chamber's pressure.
Types of ion getter pumps
We can classify ion getter pumps into three types. Each type has advantages and disadvantages.
Conventional diode (CV)
CV ion pumps provide the highest possible speed for reactive gases, as well as superior vacuum and electrical stability. However, this ion getter pump type does not allow for long-term stability for pumping noble gases.
CV pumps use a cathode material created from titanium, which reacts with getter-able gases that can be pumped through chemisorption: for example, N2, O2, H2, CO, CO2 water vapor, and light hydrocarbons.
Non-reactive noble gases are pumped mainly through ion implantation, which is why CV pumps operate at a significantly reduced speed when handling noble gases.
Differential ion (DI) or noble diode
DI, or noble diode ion pumps, perform at a slightly slower speed than CV ion pumps. However, the DI pump does allow for stable noble gas pumping at only slightly reduced speeds.
DI pumps use cathode material created from higher-priced tantalum, an extremely hard, high atomic mass material. Tantalum reflects noble gas ions as neutral particles with significantly higher energy over titanium.
The result is a much higher implantation depth.
Triode
Triode ion pumps provide stable noble gas pumping at 80% of CV pumping speed with a higher starting pressure. However, UHV speed is reduced, electrical instability is common, and manufacture is costly.
Triode pumps use grounded negative-voltage titanium rings as the cathode material and a collector plate at anode potential. Typically, the inner wall of the pump vessel serves as the third electrode.
The result is higher pumping speeds and greater stability.
Ion getter pump applications and advantages
Ion getter pumps are frequently used in general UHV systems, surface analysis, and high-energy physics applications.
As well as producing UHV pressures, ion getter pumps are:
- Hydrocarbon-free
- Operable at high temperatures
- Highly resistant to radiation and magnetic fields
- Vibration-free
- Low maintenance
- Operable without inlet isolation valves
These advantages make ion getter pumps well-suited for high-precision apparatuses. Unfortunately, they can be poor at pumping noble gasses, require high voltage, and need a turbomolecular or a secondary pump to create the starting pressure.
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