Ion Pump Types And Features
An ion pump is a type of vacuum pump used to create an ultra-high vacuum. They are also called sputter ion pump or noble pump.
1.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.
2.Types of ion pumps
We can classify ion pumps into three types. Each type has advantages and disadvantages.
(1)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 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.
(2)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.
(3)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.
3.Ion pump applications and advantages
ion pumps are frequently used in general UHV systems, surface analysis, and high-energy physics applications.
As well as producing UHV pressures, ion pumps are:
☆Hydrocarbon-free
☆Operable at high temperatures
☆Highly resistant to radiation and magnetic fields
☆Vibration-free
☆Low maintenance
☆Operable without inlet isolation valves
One of the major advantages of ion pumps is that they can achieve a high vacuum without mechanical vibration or noise because of their simple mechanism of applying voltage to electrodes in a magnetic field. For this reason, they are widely used as vacuum pumps for electron microscopes and semiconductor manufacturing equipment, which require both high vacuum and fine control.
Ion pumps themselves are not very large, and even the largest ones are usually small enough to fit on a desk.
Since the power consumption drops when there is no more gas that can be exhausted, and there is no backflow of oil or other contaminants to contaminate the area being exhausted even if the pump should stop, it is suitable for unattended operation for long periods of time, and is also widely used as a vacuum pump to maintain a vacuum.
These advantages make ion 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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