[Amps] Ion Pump

[John Lyles]

Ion Pumps are worthy of a wikipedia check. They are used in high vacuum 
systems, once the vacuum is established with a roughing pump such as a 
Roots blower style or mechanical chug-chug recipocating. They help 
maintain the vacuum absorbing small qtys of free molecules. However, 
they are mounted via a tabulation or tubing off the main vessel, so they 
have limitations. Big tubes might have a 2 liter/sec 'appendage' pump. 
They don't actually have any moving parts, using a voltage of 3000-7000 
volts DC through a current limited power supply. In particle 
accelerators, plasma sources, ion beam, or ion implantation sources, 
they might be much larger, like the size of a keg. These require power 
sources of 50 mA or so, while the little ones run off of 100 uA or less. 
In vacuum tube manufacture they are used along with another more modern 
devices called a cryo-pump. Like was said earlier, big tubes of over 100 
kW dissipation often have appendage ion pumps mounted underneath. You 
can tell the quality of the vacuum from the power supply current, and 
when the tube is heated in operation and outgasses, the spikes in 
current will indicate the event, can be used to even interlock the HV or 
bias so that the tube won't run with trashed vacuum. This helps prevent 
internal arcing from the outgassing from damaging the grids and cathode.

73
John
K5PRO