空间行波管排气过程中残余气体的质谱分析

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

电真空器件内残余气体直接影响其阴极的发射能力与寿命。本文利用高灵敏度四极质谱仪监测了空间行波管在整个排气过程中的残余气体,对各阶段气体成分及含量进行了分析。结果表明:烘烤前,水为主要气体,占80%。前期擦拭用无水乙醇易污染真空系统;升温过程中氢迅速增多,当烘烤温度达到220℃时,H_2成为系统中主要气体;整个烘排过程H_2的分压小于10-3Pa,其余气体分压均小于10^(-4)Pa;烘烤结束后,H_2分压为2. 4×10^(-8)Pa,占74%。H_2O分压为6×10-9Pa,占20%;离子泵与吸气剂泵组可有效抽除残余气体,且对H_2的抽速高于对其他气体抽速;另外,质谱仪自身会放出H_2、H_2O、CH_4、CO_2等气体,在真空系统压力达到10-9Pa范围时,质谱仪自身放气已不可忽略。

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 H2 O vapor and H2 had a major impact. To be specific,before baking,H2 O 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 H2 O（ 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.