Investigation of gas species in a stainless steel ultrahigh vacuum chamber with hot cathode ionization gauges

A residual gas analyser was used to study the gas species evolved during degassing of a stainless steel 304 ultrahigh vacuum chamber before and during bake-out of the chamber at temperatures up to 235 °C with two different types of hot cathode ionization gauge. In both cases, when the ionization gauges were turned on and degassed the dominant outgassing species were H2 and H2O. During bake-out of the chamber the main gas species detected were H2, CO (mass 28), and H2O. When the chamber was finally baked out the main gas species detected were H2 and CO, even at room temperature. These results should help to solve the problem of evolution of degassing species, which affect the achievement of ultra and extreme high vacuum. By baking the system most species are removed; the others have to be removed by alternative means.