Characterization of Residual Gases of Space Traveling Wave Tube in Degassing with Mass Spectrometer

The time-dependent concentration and partial pressure of the residual gases in baking of space traveling wave tubes (TWTs) were investigated with high sensitivity quadruple mass spectrometer. The results show that H₂O vapor and H₂ had a major impact. To be specific, before baking, H₂O vapor accounted for 80% and anhydrous ethanol was the major contaminant; as the baking temperature increased to 220℃, H₂ concentration rapidly increased; the partial pressures of H₂ and the rest residue gases were below 10^-3 Pa and below 10^-4 Pa, respectively. After cooling, the partial pressures of H₂ (2.4×10^-8 Pa) and H₂O (6×10^-9 Pa) accounted for 74% and 20% of the residue gases, respectively. Ion pump and getter pump unit, capable of effectively removing the residual gases, displayed the fastest pumping speed of H₂. We suggest that at a base pressure of 10^-9 Pa, outgassing of mass spectrometer itself may be a problem.