Research On The Technology Of The Sagittal Focusing Crystal Monochromator In NSRL-XAFS Beamline Upgrading Project

Synchrotron light source brings revolutionary force for human civilization after the source of X-ray and laser. It has become an important platform for multiple science cross research because of its excellent character of high luminance, intensity, collimation and continuous spectrum from infrared ray to X-ray. The synchrotron radiation light source and its application methods are developing faster and faster in recent years, which require higher photon flux, spatial,time and energy resolution and smaller light spot. The supporting beamline engineering is becoming more and more complicated too, which is involved with the science of vacuum,mechanism,optics and electrical control. A beamline which has rational and steady structure is the important part of the synchrotron radiation light source. Sagittal focusing crystal monochromator combines the advantages of crystal monochromator and focusing system, which has the ability not only to monochromate the synchrotron radiation light, but also focus the beam in horizontal direction, so it could get higher photon flux,intensity and smaller light spot. The sagittal focusing crystal monochromator simplifies the beamline system and reduce its price, and it has become an important research direction of the crystal monochromator in synchrotron radiation beamline.We made systemic research on key technology of the sagittal focusing monochromator for dynamical energy scanning by support of NSRL-XAFS beamline upgrading project, and got the research experience of design, manufacture and examining of the key parts. The main research content divides to several aspects as follows:1. Research on crystal bending scanning mechanism: The bending mechanism of the second crystal is the key part of the sagittal focusing monochromator. The author designed the crystal bending mechanism with double rockers around the fixed axis for the requirement of fixed light spot of XAFS measurement after surveying the international common bending modes in synchrotron radiation beamlines, and made crystal bending experiment on LTP (Long trace profiler).2. Improvement on energy scanning mechanism: The Bragg rotation axis is designed on the surface of the second sagittally bended crystal and the length of the first crystal is increased to avoid the influence to the diffraction quality and the light spot stability induced by the movement of the footprint on the second crystal. And the L-linkage mechanism is used to realize light spectrum scanning with only one dimension rotating.3. Research on crystal cooling technology: The first crystal on sagittal focusing crystal monochromator in XAFS beamline was facing to 3×0.1mrad~2 white light directly, and got high temperature. The heat deformation decreased not only the photon flux and the energy resolution of the monochromator, but also the effective experiment time because of the long time to achieve heat balance of the double crystals. The author calculated the size of the footprint on the crystal and the distribution of the heat source, and established finite element analysis models with and without water cooling respectively. We found that the simply bottom indirectly cooling could decrease the crystal temperature and heat deformation and shorten the heat balance time effectively after comparing the results of finite element analysis of the two models.4. Research on how to restrain the anticlastic bending: The author introduced the principle how the bended crystal produce the anticlastic deformation and made finite element analysis,design and offline measurement on the ribbed thin crystal and the "golden value" crystal. We got much useful data and supply stronger warrant to the engineering design of the sagittal focusing monochromator.The author is researching on the prophase viable project of the NSRL-XAFS beamline upgrading. And get the conclusion that replacing the double plane crystal monochromator with the sagittal focusing monochromator could increase the optical acceptance window and photon intensity, reduce the size of the light spot on the sample and improve the performance of the beamline. The author made a perfect optical structure which could increase the photon intensity on the sample ten times in theory after the upgrading by optimizing parameters and ray-tracing calculation based on the light source parameters and space condition.