After prolonged periods of sputtering with Argon gas, the ion pumps can become saturated, resulting in occasional “belches” of Argon during which the ion pumps overheat and release large amounts of gas. These belches usually result in a snowball effect that can dump the system. Rejuvenating the ion pumps once every few months (more often if you do a lot of sputtering) will help to prevent the belch problem from recurring.
To rejuvenate the ion pumps with O2:
1. Turn off all filaments, including the ionization tube (DIG).
2. Set the ion pump control panel meter to the 200mA current settings and set the
ion pump to the run (protected) mode.
3. Slowly bleed in O2 until there are 40mA of current shown on the ion pump panel meter. You will need to change ranges on the panel meter as the current is increased.
4. Adjust the leak valve as needed to maintain 40mA of current for 20 to 30 minutes.
5. Close the leak valve. It takes about one day for the vacuum to return to its previous level.
For more information on rebuilding ion pumps, search for Ion Pump in the RBD TechSpot blog search box.
For more information on ion pump theory, here is a link to an informative paper – https://cds.cern.ch/record/454179/files/p37.pdf
And, from Wikipedia:
An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump capable of reaching pressures as low as 10−11 mbar under ideal conditions.An ion pump ionizes gas within the vessel it is attached to and employs a strong electrical potential, typically 3kV to 7kV, which allows the ions to accelerate into and be captured by a solid electrode and its residue.
The basic element of the common ion pump is a Penning trap. A swirling cloud of electrons produced by an electric discharge are 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 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.
Both the pumping rate and capacity of such capture methods are dependent on the specific gas species being collected and the cathode material absorbing it. Some species, such as carbon monoxide, will chemically bind to the surface of a cathode material. Others, such as hydrogen, will diffuse into the metallic structure. In the former example, the pump rate can drop as the cathode material becomes coated. And, in the latter, the rate remains fixed by the rate at which the hydrogen diffuses.
There are three main types of ion pumps, the conventional or standard diode pump, the noble diode pump and the triode pump.
Ion pumps are commonly used in ultra-high vacuum (UHV) systems, as they can attain ultimate pressures less than 10−11 mbar. In contrast to other common UHV pumps, such as turbomolecular pumps and diffusion pumps, ion pumps have no moving parts and use no oil. They are therefore clean, need little maintenance, and produce no vibrations. These advantages make ion pumps well-suited for use in scanning probe microscopy and other high-precision apparatus.