Research And Application Of Variable Pitch Grating Monochromator And Spectrometer In XFEL

The discovery and application of X-rays not only has epoch-making influence on physics,but also promotes the development of many disciplines,including chemistry,life sciences,materials science,nuclear energy,medicine,etc.Synchrotron radiation X-ray source,used to developed by parasitising in first generation of high-energy physics accelerator,it now already built more than 50 devices and providing scientific research supports in world-wild,achieved various groundbreaking results in researches of material microstructure and kinetics,biological protein kinetics,etc.X-ray free electron laser(XFEL)is a strong coherent pulse X-ray which resulted from the self-excited radiation amplification from periodic magnetic field effect of high quality relativistic electron beam.Compared with traditional X-ray sources(laboratory X-ray machines,laser-driven X-ray sources,synchrotron radiation X-ray sources),XFEL has characteristics such as strong coherence(horizontal completely coherent,longitudinal partial coherent),ultra-high brightness(peak brightness is 00000 higher than synchrotron radiation X-ray),ultrashort pulse width(tens of femtoseconds to hundreds of femtoseconds),ultra-high collimation and superior light source monochrome(energy resolution 10-3),etc.,which is able to explore the evolutionary information of the microscopic and mesoscopic structure of the material with unprecedented time and spatial resolution.The development of XFEL provides pioneering methods and opportunities for innovation and breakthroughs in many basic disciplines and fields of application,such as physics,chemistry,materials science,life sciences,energy science,environmental science,information industry,besides the innovative breakthroughs of related engineerings and technologies.It also provides an unparalleled research platform for the exploration and resolution of key scientific issues in major areas of national security.Additionally,in the laser device of an X-ray free electron,beam line,experimental station,grating monochromator as well as spectrometer are all core equipment systems,whose behaviour directly affects the performance of the entire device and the results of the experiment.Therefore,study the performance and its influencing factors to optimise system design is one of the important issues in XFEL construction.In this paper,the development status of X-ray light source is introduced firstly,and then focus on the key technology research,system design,installation and commissioning methods,main achievements of XFEL beam line and experimental station in the variable pitch grating monochromator and spectrometer are introduced.1.According to the design requirements,with energy resolution higher than 5000 of the SX-700 X-ray grating monochromator,zero-order diffraction at the output of high photon flux(Pink beam)and time broadening control to less than 100fs,the physical model of the grating monochromator was established.It studied factors that effects the grating resolution,time broadening and photon output flux.Meanwhile,the design parameters of SX-700 X-ray grating monochromator are optimised through numerical simulation.It also proposed the method of improving energy resolution with low density scribe gratin,so that the full photon energy range resolution higher than 5200 while saving construction costs.Through the study and analysis of the aberration of SX-700 X-ray grating monochromator system,it is found that the inherent coma aberration can be compensated by changing the curvature of the pre-focusing lens,that is,by changing the distance of the outgoing slit Compensation,thus monochromator energy resolution has greatly improved.2.Since the X-ray resonance inelastic scattering spectrometer(RIXS)requires a high vacuum environment and a precise fitting requirement,the tilt of the optical element can not be measured directly.Therefore,based on the study of the working principle and optical path structure of RIXS,a method of measuring the inclination of optical elements with visible laser is established:without damaging the degree of vacuum of the spectrometer,the optical element is calculated by measuring the distance between the laser spot on the surface of the optical element and the reflection of the laser spot on the surface of the optical element.This method has been successfully applied to the tilt test of the RIXS optical element and the debugging of the XFEL beam line.3.The experimental method of RIXS calibration was designed,and the high precision micro-nanostructure slit and experimental samples were developed.The energy calibration was successfully performed for RIXS,which laid the foundation for the application of RIXS in PAL-XFEL beam line and experimental station.In the absence of XFEL,the E-gun(electron gun)are used to irradiate different sample materials,XES characteristic peaks adopts in debuting the RIXS spectrometer,and also used in assisting other equipments to sample surface micro-material comprehensive experiment.