Research On Electron Optics Design Of CNTs Cold Cathode Electron Gun

Carbon nanotubes(CNTs)have been widely studied for their high aspect ratio,high mechanical strength and good physicochemical stability.In vacuum electronics,the cold cathode technology based on CNTs is developing continuously.On the basis of the features of compact structure and quick start,it has gradually realized high stability of output under large current,and gradually been used in the studies of devices such as X-ray tube and ionization gauge.But to realize the application of CNTs in TWT and other microwave power devices,the characteristics of electron optical characteristics of electron gun need specific analysis and design.However,in the present study,although the electron gun with bipolar structure has a large emission current,the electron beam diverges seriously and cannot meet the requirement of laminar flow.This paper is mainly aimed at laminar electron gun and includes the following research results:(1)CNTs cathode was prepared by screen printing process,and its field emission characteristics were experimentally studied.Under the working condition of 500 Hz pulse and 4μs width,the emission current of the cathode reached 10.72 m A under the voltage of 1700V(corresponding field intensity of 8.5V/μm).The field emission characteristic parameters of CNTs were obtained by fitting the results.(2)The structure of electron gun based on CNTs with good laminar flow was established.Using CST software,a kind of curve type pre-focusing CNTs cold cathode laminar gun was designed.The optimal structure parameters of the electrode were determined.The sizes of cathode and grid are all 1 mm in diameter.Cathodegrid space is 1mm.Thickness and curvature radius of curved pre-focusing electrode are 0.5 mm and1.5mm.The electron gun was introduced into the drift tube model,and the magnetic field distribution of the magnetic focusing system was adjusted.According to the calculation,the passing rate of the electron beam reaches 100%.(3)The electrodes determined in the simulation design were prepared,and the actual electron gun was assembled and the experimental research was carried out.Finally,under the pulse voltage of 10 k V(frequency:1k Hz,pulse width: 4μs),the emission current of cathode reaches 8.37 m A,and the average gate transmittance reaches 56.3%.At the field intensity of 8V/um,the drop of current within 1h is 8.7%.In the experiment of drift tube,at 10 k V,the passing rate of the electron beam was 72%,and the current of collector reached 2.5m A.The above results show that the designed electron gun based on CNTs cold cathode has a practical prospect in cold cathode TWT in the aspects of emission current and electron beam quality.