针对空间应用对X射线源的需求,提出了一种透射式微型微束调制X射线源的设计方案,建立了调制X射线源的理论模型。相较传统的X射线源,增加了栅极电压控制和多个聚焦极微束聚焦功能,通过改变栅极电压实现X射线的幅度调制和脉冲调制。利用带电粒子光学仿真软件SIMION,模拟计算了不同管电压下透射式阳极靶的最佳靶厚,仿真分析了不同栅极电压对电子束运动轨迹的影响,最终得到了150µm的微束焦斑直径。完成了原理样机的加工镀膜和真空密封,搭建了调制X射线源的测试装置,实验报道了阳极钨靶的谱线特性,分析了栅极电压影响出射X射线强度的原因,讨论了栅极幅度调制的可能性,完成了调制X射线源栅极脉冲调制的验证。%X-ray sources have been extensively penetrated into all aspects in daily life, such as pharmaceutical analysis, X-ray diagnostics, and radioactive static elimination. Along with the burgeoning field of deep exploration, all kinds of X-ray sources are fabricated to meet the needs of space applications. Therefore a design proposal of a transmission-type miniature micro-beam modulated X-ray source, in allusion to the space application of X-ray sources, is proposed and its theoretical model is constructed. In contrast with the traditional X-ray sources, a grid electrode is added and three focusing electrodes are chosen and used. Amplitude modulation and pulse modulation of X-rays, by controlling the voltage value of the grid electrode, are realized. Electrons are restrained to pass when the grid electrode is loaded with a negative voltage and no X-ray photons are produced. When loaded with a positive voltage, the grid electrode lets electrons get through and finally reaches up to the anode electrode. Three focusing electrodes, meanwhile, are used to make the electron beam converge and finally focus on the anode target. The thickness of the transmission-type target material is considerable, considering it to be a key parameter influencing the conversion efficiency of X-rays. If the target thickness is too thin, only a part of electrons can convert into X-ray. On the contrary, when the target thickness is too thick, the produced X-ray intensity is low too. That is because some X-ray photons are absorbed by the anode target material even though all of the electrons convert into X-ray. And the optimum target thickness, in different anode voltage values and different target materials, is simulated using charged particle optical simulation software, and the results are presented in a table. In addition, the influence of grid voltage value on electron beam trajectory is also taken into account and finally a 150-µm-diameter focusing spot is obtained. The prototype model is fabricated via coating film on the anode and the single-step brazing process in a vacuum furnace. After the test platform is set up, the spectrum feature of tungsten target is attained. And it is analyzed that the X-ray intensity is related to the grid electrode voltage value. The feasibility of grid amplitude modulation and grid pulse modulation are verified in the end. As a multifunctional modulated X-ray source, it will have more important scientific significance and space application prospects, and be used in inter-satellite X-ray communication, ionization blackout area communication, planetary science, pulsar simulation and single event effect simulation of space radiation environment.
展开▼
