| Magnetron is a high-efficiency and high-power vacuum electronic device,which has a wide range of applications in military and civilian fields.At present,the magnetron adopts a hot cathode,and the cathode needs to be raised to a temperature required for operation within a certain period of time to generate thermionic emission.In the few seconds before startup,the magnetron has no microwave output,and its clutter signal can cause serious electromagnetic compatibility problems.The cold cathode has the advantages of fast startup and no heating,and is an ideal cathode to realize the fast startup of the magnetron and solve its electromagnetic compatibility.However,the current required for the operation of the cold-cathode magnetron is relatively large,and a highcurrent cold cathode is urgently needed to meet the current demand of the magnetron.Cold cathodes made of carbon nanotubes have the advantages of large current and current density,low power consumption and good electrical conductivity,and instant start-up.In this thesis,carbon nanotubes are used as cold cathode field emission materials,and theoretical calculations are carried out from the simulation of cold cathode magnetrons,and then the preparation of high current carbon nanotube cold cathodes is carried out.The specific research contents are as follows:1.Cold cathode magnetron field emission simulation.The field emission simulation of ten-cavity magnetron is carried out by finite element analysis and simulation software,and a magnetron with a minimum current of 200 m A is obtained,and the resonant frequency is 2.45 GHz.2.Preparation of high current cylindrical carbon nanotube cold cathode.The process and process of preparing high-current cylindrical cold cathodes by spin coating method were studied,and carbon nanotube films were prepared on nickel foam substrates by drop coating method.By studying the influence of different rotational speeds on the film formation,the parameters of preparing film cathodes were optimized..3.The effect of carbon nanotube content on cathode emission performance.By adjusting the ratio of different carbon nanotubes and silver paste content,the field emission test performance of the cathode with 2%,5% and 8% carbon nanotube content was compared respectively.The test data showed that under DC field emission,8 %concentration carbon nanotubes have the best field emission performance.When the field strength is 1.87V/?m,the maximum field emission current can reach 13.58 m A.The heat from the cathode could not be dissipated in time,causing the sample to burn out.4.Pulse high current field emission cathode analysis test research.In order to reduce the generation of cathode heat,the pulse field emission test was carried out,and the stability of the current near 5m A,10 m A,20 m A,70 m A,and 99.8m A was tested respectively.In the test time of 5min,it was found that the current was the smallest with the increase of the current.The change values are 0%,0%,0%,0.5%,and 3.4%respectively;secondly,the maximum emission current of pulsed field emission is tested.When the electric field strength is 3.82V/?m,the maximum current is 119.2m A.5.Research on stability test of high current field emission cathode.The time required for the field emission current to stabilize under the excitation of the pulse excitation voltage was studied,and the changes of the field emission current of different magnitudes and the same magnitude of field emission current under the same total pulse width were observed.It is found that the prepared carbon nanotube cathode not only has a large emission current,but also has a high emission stability.The current start-up time is 6?s and is not affected by the current size and pulse width. |
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