How to Select a High Vacuum Pump, Part 4: Entrapment Pumps
Entrapment (or Capture) Pumps are comprised of two primary types types:
cryopumps and ion pumps.
Cryopumps:
A Cryopump works exactly the way it sounds: by freezing ("trapping" or "capturing") gas molecules on cold surfaces called “arrays”. The most important gas to remove initially from a vacuum chamber once it has been roughed down to a point where the high vacuum pump can be turned on is water vapor, and size for size nothing does this faster than a cryopump. Once the vacuum level has reached the 1x10-6 Torr range, the other residual gases need to be trapped as well, and this process takes a little longer. The main drawback to cryopumps is that eventually the arrays become saturated, and all the gas that has been trapped needs to be exhausted to the atmosphere by allowing the arrays to rise in temperature, thus enabling the gases to be pumped away by the backing pump. The good news is that the regeneration process has become faster over the years, minimizing the downtime required.
Ion Pumps:
Though they have been around a long time, ion pumps continue to be one of the best alternatives for achieving very high to ultra-high vacuum levels. These pumps have positive and negative charges where ions are created and the residual gas in a chamber is essentially buried along with the ions on the walls of the pump. These pumps also need to be regenerated, but the systems on which they are used usually are held at very high vacuum levels thus the need to remove the captured gas is infrequent.
| Pump Type |
Base Pressure (mTorr) |
| |
|
| Cryo |
1x10-9 |
| Ion |
1x10-10 |
This article was authored by Michael A. Grandinetti. More information about Mike can be found at: http://www.linkedin.com/in/michaelgrandinetti1
IES Technical Sales is a value added technical sales, distribution, and solutions provider serving the high technology vacuum, plasma/thin film, temperature, fluid handling and metrology markets.