Pumping behavior of sputter ion pumps

The ultrahigh vacuum requirements of ISABELLE are obtained by pumping stations, each consisting of a 1000 l/s titanium sublimation pump for active gases (N2, H2, O2, CO, etc.), and a 20 l/s sputter ion pump for inert gases (methane, noble gases like He, etc.). The combination of the alarming production rate of methane from titanium sublimation pumps (TSP) and the decreasing pumping speed of sputter ion pumps (SIP) in the ultrahigh vacuum region (UHV) leads us to investigate this problem. In this paper, we first describe the essential physics and chemistry of the SIP in a very clean condition, followed by a discussion of our measuring techniques. Finally, we present our measured methane, argon, and helium pumping speeds for three different ion pumps in the range of 10-6 to 10-11 Torr. The virtues of the best pump are also discussed