强流碳纳米管阴极快脉冲重频发射特性

Fast-pulse repetitive frequency emission characteristic of high current carbon nanotubes cathode

在Cu基底上,采用催化热解生长法制备了石墨化程度较高的碳纳米管阴极.当电子束能量达到1 Me V、梯度约为60 k V/ns时,发射束流强度达到15 k A,相应密度约为1 k A/cm2,束压、束流响应快,波形间几无延时.以50 Hz重复频率、约15 GW束功率强流发射时,波形稳定,随着频率增高,稳定性降低.发射炮次达1000后,表面形貌保持完整、界面无脱附;束压与束流基本满足空间电荷限制定律,发射机理属闪络型等离子体发射,等离子体速度约为3.9 cm/μs.

With the development of high power microwave technology, the demands for electron beam repetition frequency, current density, response time and emission uniformity are higher and higher. Carbon nanotube （CNt） cathode has been widely investigated, because of its special structure and excellent field emission characteristics. CNt cathode is regarded as a thin film high current cathode, and the interface bonding will affect vacuum performance, stability, lifetime and repeat ability. The direct growth of CNt is a simple and effective means for preparing cathode. When electron energy reaches 1 MeV and the pulse upward gradient attains approximately 60 kV/ns, for CNt cathode, its the emission beam intensity reaches 15 kA and the peak bundle density attains about 1 kA/cm2, the response between beam voltage and current is fast. With the increase of repetition frequency, the emission stability decreases gradually. When the emission power is 15 GW and the emission stability repetitive frequency is 50 Hz, the cathode emission is stable. However with the increase of frequency, the stability becomes weak. When the repetition frequency reaches 100 Hz, voltage and current are almost split into two sections, and the delay time is obviously different. The relation between the voltage and the current meet the exponent law, which is different from the field emission characteristic. After a 1000 shot emission, the morphology of CNt cathode is intact, desorption from the interface of CNt does not happen. So the emission mechanism is flashover plasma emission. Through analyzing the experimental data and considering the plasma expansion effect on diode gap, the plasma speed can be estimated to be about to 3.9 cm/μs.