The choice of spectroscopic scheme in x-ray plasma diagnostics

The ray tracing codes for flat, cylindrically bent (Johann horizontal focusing and von Hamos vertical focusing geometry), elliptically and spherically bent crystal spectrometers were developed. The codes, extended by introducing the two-dimensional source and the real shape of single crystal diffraction pattern in dependence on the radius of curvature, contribute to a proper choice of experimental configuration in x-ray plasma diagnostics. A method of ray tracing the von Hamos spectrometer is presented in detail. The use of the ray tracing code to the optimization of the spectroscopic scheme is demonstrated on the analysis of gas-puff z-pinch experiment.     

A wavelength-dispersive X-ray spectrometer for in/ex situ resonant inelastic X-ray scattering studies

A wavelength-dispersive X-ray spectrometer based on von Hamos geometry for in/ex situ resonant inelastic X-ray scattering (RIXS) studies at BL14W1-X-ray absorption fine structure (XAFS) beamline of Shanghai Synchrotron Radiation Facility (SSRF) is reported. The design considerations and the operational characteristics of the spectrometer are described in detail. With a Si(444) bent crystal, the spectrometer provides an energy range from 8 to 9 keV, which enables the measurement of K-edge X-ray spectroscopy of some transition metal complexes and L-edge X-ray spectroscopy of some 5d transition metal complexes. Based on von Hamos geometry, the process of the collection of RIXS is considerably simplified. The collection of full RIXS planes of tungstic samples requiring spectral resolutions is presented, demonstrating the speciation capabilities of the instrument. Taking the series of oxide-derived copper catalysts for carbon dioxide electrochemical reduction as the research model, the in situ RIXS were measured to probe dynamic changes in electronic structure. Finally, the comparison between in situ RIXS and in situ conventional XAFS is presented, demonstrating more competitive spectral resolution of RIXS.     

Investigation of the focusing of a 50-GeV proton beam using a new crystal device

Bent crystals are used at large accelerators to deflect particle beams for extraction and collimation. Not only the deflection but also the focusing of beams by bent crystals can be required for recently formulated proposals for investigations at the Large Hadron Collider (LHC) with a fixed target. The experimental results on the focusing of a 50-GeV proton beam with a new crystal device, which can be used in a circulating beam of a large accelerator such as the LHC, have been reported.     

球面弯晶在X射线诊断中的应用

为了诊断等离子体X射线,利用X射线布拉格衍射原理研制了球面弯晶谱仪。实验采用α-石英作为其晶体分析器色散元件,晶体弯曲半径为250 mm,布拉格角为30°~67.5°;采用接收面积10 mm×50mm的X射线胶片作为摄谱器件,接收等离子体X射线谱线信息。通过在"阳"加速器装置上进行实验,得到了钛等离子体X射线K壳层激发谱线信息,其光谱分辨力可达到1 000以上,光谱带宽约为0.43 eV。     

Valence-to-core X-ray emission spectroscopy of Ti,TiO, and TiO2 by means of a double full-cylinder crystal von Hamos spectrometer

We present valence-to-core X-ray emission spectroscopy of Ti, TiO, and TiO₂ by means of a double crystal von Hamos spectrometer based on full-cylinder highly annealed pyrolytic graphite mosaic crystals. We demonstrate that, using a double crystal configuration, an energy resolution of E/ΔE ≈ 2,700 can be achieved in a compact setup using cylindrically curved optics with a radius of curvature of 50 mm. The stated energy resolution proved to be high enough to identify and determine chemical shifts of the Kβ_2,5 and Kβ″ emission lines of both oxides. The experimental results are supported by calculations with the ab initio package OCEAN and compared with literature values.     

Spectrometer for hard X‐ray free‐electron laser based on diffraction focusing

X‐ray free‐electron lasers (XFELs) generate sequences of ultra‐short spatially coherent pulses of X‐ray radiation. A diffraction focusing spectrometer (DFS), which is able to measure the whole energy spectrum of the radiation of a single XFEL pulse with an energy resolution of ΔE/E? 2 × 10^?6, is proposed. This is much better than for most modern X‐ray spectrometers. Such resolution allows one to resolve the fine spectral structure of the XFEL pulse. The effect of diffraction focusing occurs in a single‐crystal plate due to dynamical scattering, and is similar to focusing in a Pendry lens made from a metamaterial with a negative refraction index. Such a spectrometer is easier to operate than those based on bent crystals. It is shown that the DFS can be used in a wide energy range from 5 keV to 20 keV.     

New focusing multilayer structures for X-ray and VUV plasma spectroscopy

We investigate the spectral characteristics of new focusing multilayer structures used as dispersive elements in a high-transmission X-ray spectrometer with cylindrical geometry (Hamos scheme): W/B₄C structures in a wavelength range of λ = 8.0?9.5 Å and Cr/Sc structures in a range of λ = 30?40 Å (the range is not accessible for natural crystals). The results of demonstration experiments on laser-produced plasma spectra recording are considered. It is shown that the luminosity of a Hamos spectrometer with multilayer dispersive elements is an order of magnitude higher than the luminosity of grazing-incidence grating spectrographs with a comparable spectral resolution.     

High‐power‐load DCLM monochromator for a computed tomography program at BMIT at energies of 25–150 keV

The research program at the biomedical imaging facility requires a high‐flux hard‐X‐ray monochromator that can also provide a wide beam. A wide energy range is needed for standard radiography, phase‐contrast imaging, K‐edge subtraction imaging and monochromatic beam therapy modalities. The double‐crystal Laue monochromator, developed for the BioMedical Imaging and Therapy facility, is optimized for the imaging of medium‐ and large‐scale samples at high energies with the resolution reaching 4 µm. A pair of 2 mm‐thick Si(111) bent Laue‐type crystals were used in fixed‐exit beam mode with a 16 mm vertical beam offset and the first crystal water‐cooled. The monochromator operates at energies from 25 to 150 keV, and the measured size of the beam is 189 mm (H) × 8.6 mm (V) at 55 m from the source. This paper presents our approach in developing a complete focusing model of the monochromator. The model uses mechanical properties of crystals and benders to obtain a finite‐element analysis of the complete assembly. The modeling results are compared and calibrated with experimental measurements. Using the developed analysis, a rough estimate of the bending radius and virtual focus (image) position of the first crystal can be made, which is also the real source for the second crystal. On the other hand, by measuring the beam height in several points in the SOE‐1 hutch, the virtual focus of the second crystal can be estimated. The focusing model was then calibrated with measured mechanical properties, the values for the force and torque applied to the crystals were corrected, and the actual operating parameters of the monochromator for fine‐tuning were provided.     

Focusing crystal device for deflecting a divergent 50-GeV proton beam

At large accelerators, bent crystals are employed to deflect weakly divergent proton beams at the stages of extraction and collimation. We demonstrate that a divergent particle beam may be efficiently deflected using a crystal with a focusing edge. A proton beam with divergence near 1 mrad, which exceeds the Lindhard angle by a factor of 30, has been experimentally deflected by 1.8 mrad with efficiency near 15%. The proposed focusing crystal may serve as an element of a novel optical system for secondary-particle beams in the TeV energy region.     

基于超环面晶体的X射线成像诊断

设计了可用于X射线成像用的聚焦型超环面晶体谱仪,讨论了基于布拉格几何结构的超环面及球面弯曲晶体聚焦特性,给出了基于超环面晶体X射线2维单能成像的光源、晶体及探测器的最佳位置,在中国工程物理研究院激光聚变研究中心进行了X射线背光成像实验.利用超环面弯曲晶体作为成像器件,其弧矢及子午平面的曲率半径分别为290 mm及190...     

Pseudo Stark and uniaxial stress splitting of the 6955 Å zero-phonon line in LiF

The spectral resolution of quartz crystals bent to a cylindrical form by means of four rods was investigated with CuKα radiation in a reflection type arrangement. The crystal adjustment was made optically using interference fringes. With the crystal bent to a circular cylinder the deviations from exact focusing inherent to the Johann case could be measured and were found to be in agreement with theory. — Crystals bent to a logarithmic spiral have also been studied. With a 24 mm broad reflecting area (mean radius of curvature 1 m; (13¯40)-plane) an uncorrected full width at half maximum intensity of 0.43 XU or 2.25 eV was observed for the CuKα ₁ line, in agreement with double crystal spectrometer measurements.     

2D Laue focusing of X-ray radiation by a double-crystal system

The theory of the dynamic 2D focusing of an X-ray wave upon its Laue diffraction by a system of two bent crystals is developed. The reflecting planes of the crystals are perpendicular to their surfaces. 2D focusing is shown to be highly sensitive to the bending radius of the crystals and to the difference in their thicknesses. The effect of astigmatism on 2D Laue focusing is described, and conditions for stigmatic focusing are found. One-dimensional focusing inside the crystals is discussed. The spectral characteristics of a double-crystal 2D-focusing spectrometer are considered.     

Performance calculations of the X‐ray powder diffraction beamline at NSLS‐II

The X‐ray Powder Diffraction (XPD) beamline at the National Synchrotron Light Source II is a multi‐purpose high‐energy X‐ray diffraction beamline with high throughput and high resolution. The beamline uses a sagittally bent double‐Laue crystal monochromator to provide X‐rays over a large energy range (30–70 keV). In this paper the optical design and the calculated performance of the XPD beamline are presented. The damping wiggler source is simulated by the SRW code and a filter system is designed to optimize the photon flux as well as to reduce the heat load on the first optics. The final beamline performance under two operation modes is simulated using the SHADOW program. For the first time a multi‐lamellar model is introduced and implemented in the ray tracing of the bent Laue crystal monochromator. The optimization and the optical properties of the vertical focusing mirror are also discussed. Finally, the instrumental resolution function of the XPD beamline is described in an analytical method.     

Focusing of X-rays by bent crystals

The coefficient of X-ray reflection from a bent Bragg mirror is obtained on the basis of the principle of locality. The focusing of X-ray quanta by bent crystals is considered. The caustics for the X-rays reflected from the bent Bragg mirror are determined.     

Focusing crystal mirrors for X-ray diagnostics of laser-produced plasma

The paper describes an investigation of the characteristics of spherical focusing Bragg-reflection mirrors. The integral reflectivity of bent crystals at Bragg angles 80–90°, the width of the spectrum of the reflected x-rays, and the spatial resolution of the images formed by the focusing crystals are considered. Results are presented of the calculated integral reflectivity of bent silicon and quartz crystals of different orientation and in different orders of reflection. The feasibility is demonstrated of laser-plasma diagnostics using the images obtained with the aid of a multichannel x-ray microscope based on focusing crystals. Possible schemes of active diagnostics of a dense laser plasma using a monochromatic transilluminating x-ray beam are considered.Laser Plasma Laboratory, Lebedev Physics Institute. Translated from FIAN Preprint No. 143, Lebedev Physics Institute of the Academy of Sciences of the USSR, Moscow, 1989.     

准单色近平行光束的X射线源

针对准单色近平行光束X射线背光成像诊断需求,提出了一种用球面弯晶进行X射线衍射选单从而获取准直光束的新方案.在神光Ⅱ装置上,设计了基于球面弯晶X射线衍射选单准直光束系统,完成了该系统的安装、调试和实验应用,获得了准单色(10~(-3)△λ/λ10~(-2))、小发散角(2 mrad)和大辐照匀斑(直径φ500 m)的X射线光源.同时基于衍射光学和球面镜成像理论,研究了不同布拉格角对球面弯晶X射线衍射光束发散角及其像散差的影响.结果表明,布拉格角会影响球面弯晶X射线衍射光束的发散角.用控制布拉格角范围的方法有望获得发散角优于1 mrad的近平行光束X射线光源.这种准单色、极小发散度和均匀角分布的X射线光源可应用于高分辨X射线成像诊断.     

一种变曲率面晶体X射线检测技术

在惯性约束聚变光谱诊断物理实验研究中,晶体衍射后X射线光谱信号较弱,需要高收光效率及宽频谱范围的光谱诊断仪器.在传统锥面弯曲晶体基础上提出变曲率弯晶多能点成像技术,该技术具有宽频谱范围、强聚焦能力、高光谱分辨的特点.在晶体衍射成像结构设计中,由于能够确保成像光线的旋转对称性,因此在原理上可消除传统弯晶X射线衍射成像像差.利用研制的变曲率面石英晶体对钛靶X射线源进行X射线聚焦检测,并与同种材料的平面晶体进行收光效率对比,实验结果表明该变曲率面石英晶体的收光效率可以达到平面石英晶体的100倍,检测X射线能量范围为4.51~5.14keV.该晶体谱仪结合X射线条纹相机能够检测宽频谱范围的微弱X射线信号,条纹相机探测面可与晶体检测光路方向垂直布局.     

Laue弯晶聚焦特性的光线追迹研究

由于可有效降低高热负载的影响, Laue弯晶是插入件辐射高通量密度硬X射线(30 keV以上)聚焦、 准直和单色化的最有效的光学元件.研究其聚焦光学特性,对发展高性能、高稳定的Laue弯晶单色器具有重要意义. 采用自行发展的光线追迹软件较为系统地研究了Laue弯晶的聚焦特性, 分析了入射光性质及弯晶参数对聚焦光斑、焦距、发散度等主要光学参数的影响. 结果表明,衍射能量越高,聚焦光斑越小,并趋于稳定值;弯曲半径越小,聚焦光斑越小, 并在其达到一阈值时得到聚焦光斑的极小值,之后随着弯曲半径的变小,由于像差等因素的影响, 聚焦光斑反而变大;晶体越厚,聚焦光斑越大,呈线性正比关系.对于衍射光发散度, 其随着衍射能量的增大而变小,并趋于稳定值;其与晶体曲率呈线性正比关系. 同时通过研究得到弯晶各参数的合理选择范围.     

On the Theory of X-Ray Diffractional Laue Focusing on Two Bent Crystals

The Laue focusing of a spherical x-ray wave onto dynamical diffraction by a double-bent crystal system is studied. The geometrical equations of two-dimensional Laue focusing and the intensity distribution formula are derived. A high sensitivity of the two-dimensional Laue focusing to the crystal thickness and bending radii difference is revealed. It is shown that this sensitivity can be used to control the crystal thickness with accuracy up to 100 and bending radii up to 10^-2 m. The focusing process of the spherical wave inside crystals as well as in vacuum is investigated. The possibility of using the two-crystal Laue system as a lens for x-ray microscopy is studied. The spectral characteristics of a twice-diffracted wave are discussed. The spectral resolution is demonstrated to be 10⁶.     

Dynamical chaos and stochastic mechanism of high-energy negatively charged particle deflection by bent crystals

Deflection of high-energy negatively charged particles in straight and bent crystals through multiple scattering by crystal atomic strings was considered for the case in which the initial angle between the particle momentum and one of the main crystallographic axes was approximately four critical angles of axial channeling. It was shown that in a bent crystal with a small crystal thickness, when the crystal bend was less than the beam incidence angle, the beam deflected in the direction opposite to the direction of the crystal bend. At larger crystal thicknesses, the large part of the beam starts to deflect in the direction of the crystal bend. In addition, there is a group of particles that follow the crystal axis bend in the angular region of approximately the critical angle of axial channeling with respect to the current direction of the crystal axis. It was shown that in all of these deflection processes, the periodicity of the location of atomic strings in the crystal does not influence the angular distributions of scattered particles. This fact is connected with the effect of dynamical chaos in particle motion in the periodical field of bent crystal atomic strings. It was also shown that observed in a recent CERN experiment effect of beam deflection, when the angle between the initial particle momentum and the crystal axis was approximately four critical angles of axial channeling, is due to peculiarities of the stochastic multiple scattering of particles by bent crystal atomic strings. These peculiarities are connected with the effect of dynamical chaos in particle motion in crystals.