Temperature measurement of cathodes used in microwave vacuum electron devices

Microwave vacuum devices are used in a wide variety of areas, such as radar, space technology, electron accelerators, free electron lasers. The cathodes, i.e. the electron sources, are the cores of high-power microwave sources. Their performances directly determine the output power, lifetime and other properties of the microwave sources. It is necessary to know the actual temperature of a thermionic cathode. The temperatures of an impregnated cathode, a coated cathode and a cathode side (molybdenum tube) have been tested by infrared thermometer, optical pyrometer and thermocouple thermometer (platinum and rhodium-platinum).The results show that the temperature of an impregnated cathode tested by infrared thermometer and optical pyrometer is similar to that by thermocouple thermometer, so the temperatures of impregnated cathode tested by infrared thermometer and optical pyrometer are very close to the actual temperature by thermocouple thermometer. The temperatures of coated cathode tested by infrared thermometer and optical pyrometer are lower than the actual temperature of the cathode tested by thermocouple thermometer about 50 ℃.The temperatures of the cathode side (molybdenum tube) tested by infrared thermometer and optical pyrometer are lower than the actual temperature of the cathode by thermocouple thermometer about 60 ℃. Since the physical and chemical changes arise on the cathode surface, the temperatures of the cathode surface tested by infrared thermometer and optical pyrometer increase about 30 ℃ heated at about 1150 ℃ within 100 min. These results will be affected by the molybdenum processing technology on the surface of the material, coating material, thickness of the film, the film density and other factors. Infrared thermometer and optical pyrometer are strongly dependent on the thermal radiation coefficient of the test surface, and it is very difficult to accurately obtain the thermal radiation coefficient of some materials.