Research Of Ultrashort Pulsed X-ray Source And Its Application

In November 1895,the German physicist R?ntgen read his first report on X-rays,"On New Rays",and since then,people have begun to explore and develop X-rays.X-ray is a high frequency electromagnetic wave,the frequency range of 3×10¹⁶Hz～3×10¹⁹Hz,with good directionality,high single photon energy,strong penetration ability and other characteristics,widely used in aerospace,medical diagnosis and high-energy physics and other fields.As the core component of X-ray production,X-ray sources have a direct impact on the development of X-ray-related industries.At present,the traditional hot cathode X-ray source is still the mainstream way to produce X-rays,but it is limited by the filament structure and external modulation method,and its modulation rate is low,the modulation pulse is wide,and the energy conversion efficiency is low,which cannot meet the demand for nanosecond ultra-fast,ultra-short pulse width and high brightness radiation modulation source in the aerospace field.Although the large-scale X-ray generation device represented by the laser plasma X-ray source has excellent time performance,its structure is complex,the cost is high,the volume is large,and the application scenarios are severely limited.Overall,in order to achieve an X-ray source that matches the current development needs of the industry,it is necessary to innovate in the electron generation mechanism,break through the current bottlenecks such as cathode materials,modulation methods and electron beam focusing,and further improve the performance of X-ray sources.In this paper,the key technologies and applications of ultrashort X-ray pulse sources with faster modulation rate,shorter pulse width,stronger outflow and structural stability are proposed in the fields of material science,space applications and medical imaging.Firstly,based on the theory of electron optics and the characteristics of X-ray performance,a three-dimensional electromagnetic simulation model of the ultrashort X-ray pulse source is established and the simulation calculation is carried out,and the influence of the focus-electrode height and position,tube current intensity,photocathode size and structure on the spatio-temporal performance of the ultrashort X-ray pulse source is analyzed.The simulation results show that with the decrease of the height of the focus-electrode,the spatial resolution ability of the X-ray source decreases,and the modulation rate and time resolution of the system are significantly enhanced,and the electrode parameters with a photocathode radius of 19mm、the distance between the cathode and the focus-electrode is 12 mm and a focus-electrode height of 10mm are determined.The simulation results show that when the anode voltage is 30KV,the radius of the electron focal spot on the anode target is 2.14mm,which is about 0.11 times the electron emission area,indicating that the electron optical system has a good focusing ability for the electrons emitted by the photocathode.In addition,the crossing time of the electron is 1.5 ns,and the crossing time dispersion is about 238.35 ps,which is expected to achieve ultrafast X-ray generation with a pulse width of less than 5 ns and a modulation rate of 100 MHz.In addition,an ultra-short X-ray pulse source prototype was prepared,in which the integrative sensitivity of the photocathode is about 150μA/lm.And the tube flow intensity and outgoing X-ray performance were tested.Theoretical analysis and experimental results show that the maximum tube current can reach 8.8m A,and the tube current stability is high.Finally,based on theoretical analysis and simulation modeling,the application prospect of ultrashort X-ray pulse source in electromagnetic shielding environment is discussed.