- An ion pump is a type of vacuum pump which operates by sputtering a metal getter.
- Under ideal conditions, ion pumps are capable of reaching pressures as low as 10⁻¹¹ mbar.
- An ion pump first ionizes gas within the vessel it is attached to and employs a strong electrical potential, typically 3–7 kV, which accelerates the ions to into the solid electrode. Small bits of the electrode is sputtered into the chamber.
- Gasses are trapped by a combination of chemical reactions with the surface of the highly-reactive sputtered material, and being physically trapped underneath that material.
- The basic element of the common ion pump is a Penning trap.
- A swirling cloud of electrons produced by an electric discharge is 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 to 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 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. In the latter, the rate remains fixed by the rate at which the hydrogen diffuses.