What is An Ion Pump?

An ion pump, also referred to as a sputter ion pump, is a variety of vacuum pump which can operate by sputtering a gear made out of metal. Sputtering is a phenomenon in which microscopic particles are ejected from the surface. The material is itself bombarded by particles of plasma or gas. While this occurs naturally in outer space, we can create this process here on earth. Under ideal conditions, ion pumps can, amazingly, reach pressures as low as 10-11 mbar. An ion pump ionises gases within the vessel it is attached to, employing a robust electrical potential. This is typically between 3 and 7 kiloVolt and accelerates the ions into a solid electrode, with smaller pieces of the electrodes sputtered into the chamber. Gases are trapped using a combination of chemical reactions with the surfaces of highly reactive sputtered material, this being physically trapped beneath the material.

Evidence of the electrical discharge was first identified as far back as 1858 by a gentleman by the name of Julius Plucker, who performed experiments upon the subject of electrical discharges using vacuum tubes. In 1937, Frans Michel Penning found some evidence of pumping in operating his cold water cathode gauge. These effects were quite slow to pump by modern standards, and therefore not at all commercialised.  

The basic element of the common ion pump is known as a penning trap. A cloud of electrons swords around with the help of electric discharge, and temporarily stored in the anode region of a penning trap. Electrons such as these then work to ionise incoming gas atoms as well as molecules. The result is that the ions are accelerated to strike a chemically active.

Both the pumping rate as well as the capacity of such capture methods are dependent on surrounding factors. The impact of the accelerated ions will become either buried within the cathode or sputter cathode material all over the walls of the pump. The freshly sputtered chemically active cathode material acts as the getter that evacuates the gas by both processes of chemisorption and physisorption, resulting in the net pumping action.

With ion getter pumps, initial pumping is usually managed by a turbomolecular pump combination, which is used to remove the bulk gas until the vacuum level drops down to around 10-4 mbar or lower.

Following on from removing the bulk gas, a high voltage is applied via the element assembly, this results in the electrons being pulled into the cylindrical anode tube assembly. Electrons are bound together in tightly packed spiral paths with the use of a permanent magnet which is located on the outside of a vacuum chamber, resulting in plasma discharge.

The resultant ions then bombard titanium cathode plate resulting in the molecular ions occurring by implantation. The bombardment means that titanium atoms are sputtered from a cathode lattice. The result is repositories on the surrounding surfaces of sputtered film. The film then produces a gettering of gas molecules.