ion pump


Once a low pressure is achieved, it can also be maintained by and ion pump. An ion pump needs no backing from a roughing pump. Schematically, an ion pump looks like this


The rest gas in that pump is ionized by a plasma discharge due to the high voltage between anode and cathode. The ionization probability is increased by the presence of the magnetic field which makes the electrons travel on spiral trajectories. When the ions hit the Titanium cathode they can be buried in it or react with it. Additionally, Ti is sputtered off the cathodes and deposited on other parts of the pump. This Ti can react with the rest gas and increases the pumping effect. The ion pump does not remove the rest gas from the system. It just binds it such that it can not contribute to the pressure any more. The current provided by the high-voltage power supply is proportional to the pressure in the system. Ion pumps can therefore be used to estimate the pressure. The ion pump can be operated at pressures between

10-3 mbar and 10-11 mbar. Using the pump at high pressure will decrease its lifetime. Most ion pumps are not particularly good at pumping hydrogen.

An important thing to remember when using an ion pump is to put it in a protected operation mode once it is running at low pressure. In case of any vacuum accident, this will turn off the pump once the ion current increases too much.


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