覆Os膜M型阴极高发射性能随真空度变化的研究

Influence of Pressure Increase on High-Emission of Os-Coated M-Type Cathode

在覆Os膜M型阴极工作于75 A/cm2高电流密度的情况下,逐级降低真空系统的真空度,测出了阴极电流密度随真空度变化的关系曲线。分析表明,当系统真空度为1.0×10-5Pa时,阴极发射开始出现明显下降,下降幅度达1.96%;当真空度为2.07×10-4Pa时,阴极电流密度降低10%,阴极寿命接近终了。进一步研究认为,对于微波管而言,通过渗漏进入微波管内的大气特别是其中的氧分子,将阴极表面的Ba+(a)转变为Ba2+,使得阴极表面的发射单元逐步丧失电子发射能力;与此同时,真空度降低带来的离子轰击使得离子斑区域的覆膜层消失,导致该区域功函数升高。两种因素的共同作用,使得微波管中阴极的发射性能逐步下降。

The influence of the pressure increase in a small multiple-beam klystron on the Os-coated M-type cathode,operating at a peak current density of 75 A/cm2,was experimentally studied.The relationship between the pressure and the emission current density was plotted.According to the plot,at 1.0×10-5 Pa,the current density was found to decrease by 1.96%;at 2.07×10-4 Pa,the current density dropped by 10%,and the cathode was found to be dying.The leakage-induced degradation possibly originated from two major factors：one is the oxidation of Ba＋（a）into Ba2＋on the surface,inversely affecting the surface emission;the other is the de-activation of the emission sites by ion sputtering,resulted from the leaked-in gases,oxygen in particular.We concluded that the leakage accounts for the emission degradation.