Ion pump (physics)

An ion pump works by creating an electric field across a fluid containing ions. An ion is an electrically charged atom or molecule. If the fluid does not naturally contain ions, then it must be ionized before an ion pump will work. A fluid is ionized either by addition of an ionic substance, or by electrostatic discharge (ESD) caused when the electric field strength exceeds the dielectric strength (approximately 30 kV/cm in air [http://hypertextbook.com/facts/2000/AliceHong.shtml] ). By exerting an electric voltage across two insulated or uninsulated electrode surfaces on either side of the fluid, an electric force is exerted on each charged particle within the fluid. The force magnitude on each particle is equal to the product of the electric field strength and the electric charge of the particle, (note that the direction of the force depends on the sign of the charge). The net pressure created by the pump will be the summation of the electric forces divided by the cross sectional area of the pump. If the fluid contains any non-charged particles, then these will be pushed along by the charged particles to the extent that the fluid is viscous.

Ion pumps are very different from a conventional mechanical pumps, such as a rotary pump or a turbomolecular pump because they do not have any solid moving parts. Like mechanical pumps, ion pumps are flow reversible. They are also reversible in the sense that they can be used as a pneumatic or hydraulic generator to convert fluid pressure and flow into electrical voltage and current.

Applications

Some small high-end air ioniser (air-filtration) devices use an air ion pump to move air without the use of a fan.

An ion getter pump [ [http://accelconf.web.cern.ch/accelconf/p67/PDF/PAC1967_0831.PDF 1967 - Penning discharge ion getter pump] ] is a vacuum pump that works by ionizing the residual gases in a partial-vacuum so that they can be adsorbed to a special material, known as getter, on the walls of the pump. This process is known as gettering. Ion pumps can operate efficiently at extremely low pressure, in the range of 10⁻³ to 10⁻¹² torr. This is because an ion pump applies a force directly to the remaining particles, while a mechanical pump must wait for the particles to randomly bounce into the pump before they can be extracted.

An ion getter pump acts similarly to a cold cathode ion gauge, allowing the residual gas pressure to be measured by determining the electrical current through the pump. This is possible because the gas pressure is a function of the number of molecules in a volume, (see gas law). When the electrical conductor is uninsulated and the ions contact it, then the electrical current is a function of the average ion charge and the number of ions per second that contact the electrode. An electric current is defined as the rate of flow of electric charge. So a flow of ions is a form of electric current. When the ions contact the electrode, their charge is neutralized. According to Kirchoff's current law, the two currents must be equal and opposite.

ee also

* Magnetohydrodynamic generator (MHD) - Another type of pump/generator with no moving parts, using ion currents in a magnetic field.

Sources

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External links

* [http://cas.web.cern.ch/cas/Spain-2006/PDFs/Audi.pdf An Introduction toIon Pumps]
* [http://www.vacuum-guide.com/high_vacuum_pump/getter_ion/getter_pump_europe.htm www.vacuum-guide.com] - ion getter pump manufacturers directory.
* [http://www.gammavacuum.com www.gammavacuum.com] - ion pump manufacturer.