Performance Evaluation Method And Experimental Research Of Thermionic Cathode Used In High Power Gyrotron Traveling Wave Tube

High-power gyrotron travelling-wave tubes（gyro-TWTs）are widely used in the field of microwave technology,which can improve the power and quality of microwave signals.They are an important part of microwave communication,radar,medical imaging,and other fields.Currently,most high-power gyro-TWTs use dispenser cathodes as emission sources,which have high electron emission efficiency,long life,and high stability.In recent years,in order to meet the increasing demands of engineering applications,the structure of cathodes has been innovated.However,there is a lack of systematic research on the comprehensive performance evaluation of cathodes.This thesis takes the performance evaluation of cathodes for high-power gyro-TWTs as the research topic,focusing on the performance of two kinds of cathodes,film-coated（M-type）and scandate cathode,in close-distance water-cooled anode diodes and magnetron injection electron guns.The following results obtained important conclusions in several aspects:1.The test results of near-distance water-cooled anode diodes show that the Richardson work functions of M-type and scandate cathodes are 1.98 and 1.68 e V,respectively.At the same operating temperature,the maximum space-charge-limited current density J_div and the zero-field current density J₀ of the scandate cathode are about1.8 times that of the M-type cathode.The low-temperature emission capability of scandate cathodes is greater than that of M-type cathodes.In the diode test,the M-type cathode exhibits uniform emission characteristics,while the scandate cathode exhibits a typical abnormal Schottky phenomenon.M-type cathodes are suitable for gyro-TWTs that require high emission uniformity,while scandate cathodes are suitable for gyro-TWTs that require high cathode current density emission.2.In order to find out the reasons for the unstable emission of impregnated dispenser cathodes in the gyro-TWTs and the inconsistent performance of batches.Two kinds of pressed cathodes,Ba Al₂O₄ and Ba₃Ca Al₂O₇,were prepared and tested for electron emission performance.Combined with the phase analysis of impregnated materials,it was deduced that Ba Al₂O₄ would not help cathode emission and was an ineffective active material.If the production of Ba Al₂O₄ phase can be avoided in the preparation of hot cathode impregnated materials for gyro-TWTs,the quality of cathode products can be improved.3.The magnetron injection electron gun at high-voltage test was carried out on the M-type and scandate cathode.The volt-ampere characteristic curves of the M-type cathode under different duty ratios meet the requirements of the gyro-TWTs.When the working temperature of the cathode is near 1000℃,the electron beam of 10 A can be generated.The volt-ampere characteristic curves of scandate at different duty cycles show unsaturated characteristics,which may be related to the abnormal Schottky phenomenon.The emission performance of the scandate cathode is better than that of the M-type cathode.At low temperatures（800-900℃）,it can meet the requirements of gyro-TWTs with an operating of above 10 A,and can also be applied to high-power amplifiers with high current.