Ion pump

An ion pump (also referred to as a sputter 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 a solid electrode. Small bits of the electrode are 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. An ion pump (also referred to as a sputter 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 a solid electrode. Small bits of the electrode are 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 first evidence for pumping from electrical discharge was found 1858 by Julius Plücker, who did early experiments on electrical discharge in vacuum tubes. In 1937, Frans Michel Penning observed some evidence of pumping in the operation of his cold cathode gauge. These early effects were comparatively slow to pump, and were therefore not commercialized. A major advance came in the 1950s, when Varian Associates were researching improvements for the performance of vacuum tubes, particularly on improving the vacuum inside the klystron. In 1957, Lewis D Hall, John C Helmer, and Robert L Jepsen filed a patent for a significantly improved pump, one of the earliest pumps that could get a vacuum chamber to ultra-high vacuum pressures. 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.