Study Of Electron Gun Based On Cnt Cathode With Large Current

Carbon nanotubes (CNTs) have been known as the great candidate in the electronic vacuum devices on account of the outstanding characteristics including large current density, radioresistance, simple and low-cost fabrication, working at room temperature. Compared with the other cathodes, e.g. the thermal cathode, the CNTs field emission cathode has an extensive application prospect as a novel electron source. However, many problems still exist in the practical electron gun of the CNT cathode due to the different mechanism and properties, such as the divergence of electron beam. In order to obtain the optimized design and modulation, both diode and triode structure of CNT cathode were investigated in this thesis based on previous researches.In the test based on diode structure, CNT cathode was prepared by the screen printing method. The field emitters were measured in a vacuum-sealed diode tube with water cooling anode. Under the cooling water condition, the highest current density of 4.1 A/cm2 (current:20.60 mA) was obtained. Besides, the diode structure was also measured under the pulse mode, respectively.Based on the experimental data of diode structure, the simulation model of CNT field emission cathode was subsequently established. A novel triode structure including both Pierce cathode and Focus-Functioning-Gate was specifically proposed due to the divergence properties of electron beams, and the structure parameters were optimized. The emission and modulation curves of the fabricated electron gun were acquired under the DC voltage and pulse signal supply. Finally, a gate-control with low-capture electron gun comprising shadow grid and control grid was proposed based on the properties of experimental data.