| Cathodes are the electron sources of vacuum tubes.Hot cathodes have been widely used in satellite communications,radar and other defense engineering or military electronic equipment for many years,due to their high emission current and stable performance.Among the various properties of cathodes,emission current and service life are two key performance parameters.In order to further improve the performance of existing hot cathodes,this paper proposes to comprehensively utilize the thermal-photon emission mechanism to improve the hot cathode emission capability or reduce their working temperature to increase their lives.The main research work includes:Based on the analysis of the cathode thermal-photon electron generation-diffusion-emission process,using the electron diffusion equation and based on the assumption of equal-probability absorption below the Fermi level,a new thermal-photon emission model is proposed,which can be used to estimate the thermal-photon emission current density.Based on this model,we calculated and analyzed the effects of temperature,optical wavelength,optical power and anode to cathode voltage on the photon-induced enhancement of thermal emission and photon-thermal emission using MATLAB software,with the calculation results compared with those based on the Flower model..We built a thermal-photon emission performance detection platform,and tested thermal-photon electron emission performance of some tantalum-tungsten-cathode vacuum diodes on it.The effects of different working conditions such as heat,light and voltage on the thermal-photon emission enhancement performance were studied,with the experimental results compared with theoretical results.The experimental results show that the photon induced enhancement of thermal emission current increases with temperature in high temperature region,which is consistent with the calculation results of our model,but different from the classical Fowler formula results which haven't show any change with temperature;photo-thermal The photon induced thermal emission enhancement appears to decrease with wavelength increasing,which is the same as the theoretical expectation;At a given voltage,the photon induced thermal emission enhancement current increases along with the increase of optical power at first,and then saturates;the thermal-photon emission current density increases linearly with the increase of anode voltagewhen anode voltage is below a knee voltage,and then saturates.The higher the temperature,the higher the knee voltage and the higher the saturated thermal-photon emission current density.The photon induced thermal emission enhancement current has a non-monotonic relationship with anode voltage.The maximum enhancement current value is reached near the knee voltage,and the higher the temperature,the wider the width of the curve peak.A maximum quantum efficiency of 6.0×10-2was obtained using a ultraviolet light sourcewith the center wavelength of 370 nm,and spectrum width of 50 nm.The comparison between experimental results and theoretical results shows that the model established in this paper is more suitable for the estimation of cathode thermal-photon emission capability than the classical Fowler model,especially for the analysis of photon induce thermal emission enhancement in high temperature regions. |
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