电子轰击材料出气性能

Degassing Behavior of Vacuum Electronic Materials Bombarded by Electron Beam

固体材料在大气中会溶解、吸附一些气体,当材料置于真空环境下,就会因气体解溶、解吸、电子轰击等而发生放气。电真空微波器件广泛应用于加速器、卫星通信、可控热核聚变、全球定位及未来军事前沿的高功率微波武器等方面,其制造过程中非常关键的步骤是真空获得。为提高微波电真空器件研制过程中的管内真空水平,本文研制了高精度真空材料放气测试装置。系统采用小孔流导法测试出气率,极限真空低于5.0×10^(-7)Pa。利用本装置进行了电子轰击材料出气的试验研究。实验表明无氧铜在脉冲电子束轰击下出气速率与电压、频率、脉宽成正比;电子轰击的材料暴露大气后,在电子束轰击下出气速率在短时间内迅速降低到以前的放气率水平。采用四级质谱仪对电子轰击时真空室内的残余气体成分进行了分析,其主要成分为H_2(2),其它成份依次为H_2O(18),N_2(28),和CO_2(44)。对电子轰击材料出气机理进行了分析。金属电离规管进行的电子轰击除气实验研究也证明了这些实验结果。因此利用热阴极或电子枪作为电子发射源,对微波电真空器件收集极、阳极等金属材料进行电子轰击除气,将是制造长寿命高可靠微波电真空器件所必要且可行的方法。

The impact of the electron bombardmenton degassing behavior of vacuum electronics materials was investigated and exemplified withoxygen-free copper. The outgassing rate was precisely measured in orifice conduct- ance method with the lab-built test-platform at a base pressure of 5.0 ×10^ -7 Pa. The results show that the degassing rate of O-free Cu was linearly proportional to the voltage, width and frequency of the pulsed electron beam. The che- mi-sorbed single atoms dominated the bombarded Cu-surface after exposure to air for 150h, possibly because of the surface charge accumulation ; and the previous lowest outgassing-rate was rapidly reached after removal of the chem- isorbed species by electron bombardment. The desorbed gases were identified as H2, H2O,N2 and CO2. We suggest that the reliability and service lifetime of microwave vacuum devices may be significantly improved by degassing the anodes and/or collectors with the electron beam emitted from hot-cathode and/or electron guns.