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.
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