Ion Pump (physics)

An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump capable of reaching pressures as low as 10−11 mbar under ideal conditions. An ion pump ionizes gas within the vessel it is attached to and employs a strong electrical potential, typically 3kV to 7kV, which allows the ions to accelerate into and be captured by a solid electrode and its residue.

The basic element of the common ion pump is a Penning trap. A swirling cloud of electrons produced by a Penning discharge are temporarily stored in the anode region of a Penning trap. These electrons ionize incoming gas atoms and molecules. The resultant swirling ions are accelerated to strike a chemically active cathode (usually titanium). On impact the accelerated ions will either become buried within the cathode or sputter cathode material onto the walls of the pump. The freshly sputtered chemically active cathode material acts as a getter that then evacuates the gas by both chemisorption and physisorption resulting in a net pumping action. Inert and lighter gases, such as He and H₂ tend not sputter and are absorbed by physisorption. Some fraction of the energetic gas ions (including gas that is not chemically active with the cathode material) can strike the cathode and acquire an electron from the surface neutralizing it as it rebounds. These rebounding energetic neutrals are buried in exposed pump surfaces.

Both the pumping rate and capacity of such capture methods are dependent on the specific gas species being collected and the cathode material absorbing it. Some species, such as carbon monoxide, will chemically bind to the surface of a cathode material. Others, such as hydrogen, will diffuse into the metallic structure. In the former example, the pump rate can drop as the cathode material becomes coated. And, in the latter, the rate remains fixed by the rate at which the hydrogen diffuses.

There are three main types of ion pumps, the conventional or standard diode pump, the noble diode pump and the triode pump.

Ion pumps are commonly used in ultra high vacuum (UHV) systems, as they can attain ultimate pressures less than 10−11 mbar. In contrast to other common vacuum pumps such as turbomolecular pumps and diffusion pumps, ion pumps have no moving parts and use no oil. They are therefore clean, need little maintenance, and produce no vibrations which are an important factors in areas of experimentation such as scanning probe microscopy.

Recent work has suggested that species escaping from ion pumps can influence the results of some experiments.

Not to be confused with the ionic liquid piston pump or the ionic liquid ring vacuum pump.