Residual gas survey of stainless steel 304 extreme high vacuum chamber with hot cathode ionization gauge

The residual gas in a high vacuum chamber comes from a continuous outgassing which is a main obstacle in achieving the extreme high vacuum (XHV). To decrease the outgassing of hydrogen is the most prominent and persistent challenge to achieve the XHV. Another source of outgassing is from the hot cathode ionization gauge (HCIG) which has been used as a reference gauge for XHV. As the vacuum chamber of stainless steel is baked up to 320 °C, the gas species of outgassing are analyzed by QMS (quadrupole mass spectrometer). After reached at a high vacuum of ∼2 × 10−9 Pa, the outgassing from the hot cathode ionization gauge is mainly from the residual hydrogen molecules, which is compared with other gas species such as H2O, CH4, CO, C, and CO2.