Starting pressure

All ion pumps require rough pumping of the vacuum system prior to operation. The range to start diode ion pumps is <10-4 mbar or lower. At this pressure ionisation is confined to within the anode structure of the pumping element. When ionisation occurs outside of the pumping element, the power supply is not able to maintain the electric field. The power supply sees a virtual "short" due to the electric conduction of charged particles. Ion pump controllers monitor this condition and limit the power output to protect the supply and pump from damage.