| As the electron source of vacuum microelectronic devices,the emission ability of cathodes directly affects the device performance.Thermionic cathodes have the advantages of large emission current and long working life,thus have been widely used in various vacuum electronic systems and equipments.In order to explore the method of using thermal-photon electron emission to improve the performance and stability of cathodes,and to improve the simulation and design abilities of corresponding vacuum device,this paper further researches on graphene-coated barium-tungsten cathode diodes to improve cathode emission performance,and detection methods with higher stability and accuracy on thermal-photon electron emission performance detection,as well as fast time-domain simulation technology of corresponding electron gun.The content of this paper are listed as follows:Firstly,relevant theories and studies on thermal-photon electron emission,graphene related vacuum electronic devices and technologies,and time-domain simulation techniques of electron guns were summarized.Then,the process of graphene coating on tungsten substrate was studied,based on which a graphene-coated barium-tungsten cathode diode was made;and a graphene-coated barium-tungsten cathode triode structure was proposed and designed,with the emission adjustment characeteristic modeled and analyzed using MATLAB.Simulation results show that the graphene-coated barium-tungsten cathode triode can improve or adjust the cathode emission performance by changing the gate voltage.To solve the problem of large-noise in the existing thermal-photon electron emission performance detection system using the time-domain test method,the test system was improved,and a new scheme based on spectral domain testing was designed to detect the enhancement of photon-induced thermal emission increasing.The effects of different experimental factors(anode voltage,temperature,light wavelength)on the emission of an M-type-cathode thermal-photon diode were studied and compared with the two theoretical calculation results.The results show that the larger the anode voltage is,the greater the photon-induced thermal emission enhancement current is,and the faster it increases with temperature;as the temperature rises,the photon-induced thermal emission enhancement current increases firstly and then decreases,reaching a maximum at 900K;the thermal-photon emission current has the largest increment at the incident light wavelength of 380nm.Experimental results of anode voltage and temperature have a consistent trend with theoretical calculations.Furthermore,emission performance of the graphene-coated barium-tungsten cathode diode was detected.The result shows that the cathode can provide current density of not less than0.235A/cm~2 at 800℃.And the estimated work function of the cathode should be significantly less than 2e V.Based on existing electron gun time-domain simulation program,EGunSim,of our research group,the functions of the program were improved and the simulation speed accelerated:thermal-photon emission current calculation and adjustment module was added;the entire software program was transplanted to C Language platform,and CUDA parallel algorithm was used to accelerate the electron beam simulation module;and the user interface was improved.Simulation time before and after acceleration shows that compared with the original serial calculation program,CUDA parallel computing has achieved a maximum acceleration factor of 3.3 and 14.2 times under low and high precision simulation conditions respectively,which verifies the feasibility of the acceleration scheme.Work in this paper promoted the development of performance testing,simulation analysis and design technology of high-efficiency adjustable graphene-coated barium-tungsten cathode thermal-photon emitting devices. |
