微型微焦斑X射线闭管及阴极丝电子发射差异性

行星岩石成分原位测量是行星探测的基本需求，X射线荧光分析是开展元素成分测量的重要技术手段。针对深空探测X射线荧光分析仪的需要，设计并研制了一款微型微焦斑X射线闭管，尺寸为Φ15 mm×22 mm，焦斑尺寸230μm，工作时阳极接地，阴极接浮地负高压，最大电压为–50 kV。在微型X射线闭管研制过程中，开展了螺旋型钨丝、直线型钨丝、直线型铼钨丝等常用热阴极的电子发射差异性研究，测量了各型热阴极的电子发射效率。结果显示，在200 V阳极电压下，低铼含量直线型铼钨丝电子发射效率最大为27.87μA·W^–1，是螺旋型钨丝的4倍，直线型钨丝的9倍；掺铼钨丝电子发射效率远高于纯钨型阴极丝。此外，铼钨丝还具有电子发射快、预热要求低、对真空度要求不高等特点，是深空探测X射线闭管阴极丝较理想的选择。

Miniature Micro-focal X-ray Closed Tube and Electron Emission Difference of Cathode Wire

In-situ measurement of planetary rock composition is the basic requirement of planetary exploration, and X-ray fluorescence analysis is an important technical means to carry out elemental composition measurement. In order to meet the needs of X-ray fluorescence analyzer for deep space detection, a miniature X-ray closed tube with micro-focal spot is designed and developed. It size is Φ15 mm×22 mm, and the focal spot size is 230 μm. The anode is grounded in operation, and the cathode is connected to the floating negative high voltage with the maximum voltage of –50 kV. In this paper, the differences of electron emission of common hot cathodes such as spiral tungsten, linear tungsten and linear rhenium tungsten hot cathodes, are studied in detail, and the electron emission efficiency of each hot cathode is measured. The test results show that the maximum electron emission efficiency of linear rhenium tungsten wire is 27.87 μA·W–1 at 200 V anode voltage, which is 4 times that of spiral tungsten wire and 9 times that of linear tungsten wire. In addition, rhenium tungsten wire has the characteristics of fast electron emission, low preheating requirement and low vacuum requirement, so it is an ideal choice for X-ray closed tube cathode wire for deep space exploration.