An ion pump works by creating high voltage, which removes some of the electrons from the atoms in the air. This then creates positive ions, which are attracted to negatively charged electrodes which creates continuous air movement in the system.
The investigation and the resulting developments of electronic vacuum pumping by Robert Jepsen in 1957 led to the production of the world's first sputter ion pump; which was later named the Vaclon pump. This pump was developed for the purpose of being an appendage pump for maintaining Ultra High Vacuum (UHV) within microwave power tubes after processing.
Ultra High Vacuum Technology
Today, we know that the UHV technology in applications such as medical particle accelerators, high energy physics and surface science experiments is based upon the use of all-metal bakeable vacuum systems. This remarkable technology was developed in conjunction with the application of the Vaclon pump.
Previously, UHV research required glass chambers - this was found to be wholly commercially impractical. It was shown that stainless-steel vacuum systems had low outgassing rates, comparable to the use of glass - it was seen that the use of glass was not required. For example, low UHV pressure gauges which are often referred to as Helmer gauges, were evaluated for the first time in a stainless-steel enclosure.
One of the very first large scale installations of ion getter pumps was at the Hadron Collider. The getter pumps were installed to the ISR (Intersecting Storage Rings), these ran at the European Organisation for Nuclear Research (CERN) in Geneva. For this installation, and the manufacturing of the ion pumps to equip CERN, a new factory was opened.
It was at this new factory that it was discovered that combining sputter ion pumps and titanium sublimation pumps (TSP) could in theory lead to pressures as low as 10-12 , however there were important limitations to consider when starting and operating sputter ion pumps at high pressures.
The TSP is used in conjunction with an ion pump to improve pumping efficiency. It works by evaporating a titanium film onto the cryopanel or the TSP shield. The titanium film is very reactive and so the gas molecules in the chamber that collide with the cryopanel wall will react with the titanium and stick. The titanium film also helps to replenish the ion pump elements.
Operation at High Pressure
At the time, sputter ion pumps were the only existing oil-free pumps for the vacuum range below 10-4Pa, but there were many associated problems involved at their operation at a higher pressure - including the high power dissipated with consequent high temperature an outgassing, and Argon instability, short circuits and arcing and an overall limited pump life.
There was a lot of time and effort put into research and development which focused exclusively on extending the operation of sputter ion pumps towards high pressure - the combination of high evaporation rate sublimators with sputter ion pump pumping, systems were then designed for operation at 10-2Pa, achieving speeds of thousands of litres per second.
A new era in the development and application of sputter ion pumps began with the advent of oil free turbomolecular pumps and their corresponding oil free roughing pumps, which became the perfect complement to sputter ion pumps in the higher range of pressures. As a direct consequence of this, the application range for ion pumps became more evidently defined as UHV.