The beam-based calibration of an X-ray pinhole camera at SSRF

A pinhole camera for imaging X-ray synchrotron radiation from a dipole magnet is now in operation at the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. The electron beam size is derived by unfolding the radiation image and the point spread function (PSF) with deconvolution techniques. The performance of the pinhole is determined by the accuracy of the PSF measurement. This article will focus on a beam-based calibration scheme to measure the PSF system by varying the beam images with different quadrupole settings and fitting them with the corresponding theoretical beam sizes. Applying this method at SSRF, the PSF value of the pinhole is revised from 37 to 44 μm. The deviation in beam size between the theoretical value and the measured value is minimized to 4% after calibration. This optimization allows us to observe the horizontal disturbance due to injection down to as small as 0.5 μm.     

Parametric X-ray radiation as a beam size monitor

We propose two new approaches, referred to as the local and remote methods, for measuring electron beam sizes using parametric X-ray radiation. Using the local method, we have carried out a proof-of-principle experiment, and good agreement was obtained with the results of a standard method using a fluorescent screen. For the remote method, we have proposed a scheme to measure beam sizes using a Fresnel zone plate as an X-ray lens. These methods may prove useful for measuring the sizes of electron beams with small emittances or short bunch lengths in recent advanced accelerators.     

上海光源硬X射线相干衍射成像实验方法初探

相干X射线衍射成像方法是一种先进的成像技术,分辨率可达纳米量级.国际上大多数的同步辐射装置和自由电子激光装置都建立了该成像方法,并有将其作为主要成像技术的趋势.上海光源作为目前国内唯一的一台第三代同步辐射光源,尚未建立基于硬X射线的相干衍射成像实验平台.随着一批以波荡器为光源的光束线站投入使用,使得该方法的建立成为了可能.本文基于上海光源BL19U2生物小角散射线站,通过有效的光路设计,搭建了相干衍射实验平台,在12 keV和13.5 keV能量点均获得了硬X射线相干光束,并基于小孔衍射测量了入射光束的空间相干长度.该平台支持常规和扫描相干衍射实验模式,对小孔衍射图样及波带片扫描衍射图样实现了正确的相位重建,证明了该平台初步具备开展硬X射线相干衍射成像实验的能力.硬X射线相干衍射成像实验平台为国内首次建立,将为国内该实验方法的发展和应用提供有效的软硬件支持.     

Parametric x-ray radiation generated by 5.7-MeV electrons in a pyrolytic-graphite crystal

Parametric x-ray radiation is observed in a mosaic pyrolytic-graphite crystal irradiated with a 5.7-MeV electron beam. The first-order (002) reflection of parametric x-ray radiation is detected in Bragg geometry. In the measured spectra, there is a peak at about 8 keV. The detector used is arranged at an angle of Θ_D=2Θ_B=27° with respect to the electron beam, where Θ_B is the Bragg angle. The target thickness is 0.3 mm. The spectra of parametric x-ray radiation are measured at various angles of target orientation with respect to the axis of the incident-electron beam.     

A Real-time System For Measuring Spot Size of High Energy Accelerator Using Thick Pinhole Imaging

In order to easily measure the beam spot size of high energy electron accelerators with internal target enclosed,a real–time system, based on thick pinhole imaging technique, is employed. The experimental result on a 15MeV electron linear accelerator is also presented. In this paper the principle of thick pinhole imaging and the processing of data are introduced. The usual "sandwich" method needs to develop X-ray films, while debugging the accelerator parameters it will take a lot of time. On the contrary, X–ray pinhole imaging method can make a real–time measuring: as the accelerator parameters change, we can observe the beam profile's variation on the computer screen. Then when debugging we can have a definite object in view, and adjust the accelerator parameters more efficiently.     

Detailed characterization of polycapillary focusing x-ray lenses by a charge-coupled device detector and a pinhole

A method to measure the detailed performance of polycapillary x-ray optics by a pinhole and charge coupled device (CCD) detector was proposed in this study. The pinhole was located between the x-ray source and the polycapillary x-ray optics to determine the illuminating region of the incident x-ray beam on the input side of the optics. The CCD detector placed downstream of the polycapillary x-ray optics ensured that the incident x-ray beam controlled by the pinhole irradiated a specific region of the input surface of the optics. The intensity of the output beam of the polycapillary x-ray optics was obtained from the far-field image of the output beam of the optics captured by CCD detector. As an application example, the focal spot size, gain in power density, transmission efficiency, and beam divergence of different parts of a polycapillary focusing x-ray lenses (PFXRL) were measured by a pinhole and CCD detector. Three pinholes with diameters of 500, 1000, and 2000 μm were used to adjust the diameter of the incident x-ray beam illuminating the PFXRL from 500 μm to the entire surface of the input side of the PFXRL. The focal spot size of the PFXRL, gain in power density, transmission efficiency, and beam divergence ranged from 27.1 μm to 34.6 μm, 400 to 3460, 26.70% to 5.38%, and 16.8 mrad to 84.86 mrad, respectively.     

非相干照明条件下的ptychographic iterative engine成像技术

在传统多波长相干衍射成像理论的基础上提出适用于 X-射线和电子束等非相干光源照明成像的改进多波长ptychographic iterative engine 方法, 同时将小孔形状和照明光谱信息用于叠代计算, 可以在非相干照明条件下精确重建出物体的强度透射像和相位透射像, 并对光源带宽对重建精度的影响进行了分析, 对于解决如何在非相干照明条件下对大尺寸物体进行精确相位成像的问题具有较好的科研和实用价值.     

Investigation on the pseudospark electron beam and its applicationfor the generation of soft X-rays

An investigation on the pseudospark electron beam is presented in this paper. Time-integrated and time-resolved pictures of the X-rays generated by the electron beam are taken with a special X-ray pinhole camera. They show the spatial and temporal development of the pseudospark electron beam. Time-integrated pictures indicate spatial instabilities of the electron beam caused by a bent or broadened electron beam due to space charge effects. The results of the time-resolved measurements show X-ray emission only during two short periods at the very beginning of the discharge before the beam current reaches its maximum. Only during these periods does the electron beam contain high-energy electrons. In between these two periods the energy of the beam electrons decreases because of a space-charge-limited beam transport     

P-型半导体探测器在放射治疗中的剂量特性研究

电子束半导体探测器的测量精度易受到射线的能量、剂量率、入射方向和环境温度等条件的影响。此外,电子束测量射野中半导体探测器的存在将干扰均匀射野剂量场的正常分布。通过对P-型电子束半导体探测器在不同的电子束照射条件下的实际剂量测量,定量地评估了不同照射条件下电子束半导体探测器的剂量特性,以及它对电子束均匀照射野扰动的影响。The measurement accuracy of electron beam by using semiconductor detector is easily affected by beam energy, dose rate, beam incidence direction, environment temperature etc. Furthermore, the presence of the detectors on the patient surface perturbs the distribution of the radiation field. In the paper, the dose characteristics of semiconductor detector are quantitatively discussed. The perturbation of the symmetrical radiation field is investigated based on the measured results of P-type electron beam detector under different clinical conditions.     

X-ray transition radiation of electrons with energy of 300 to 900 MeV in periodic multifoil radiators

Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated.     

Si Micromachined Pinhole and Surrounding Photodiode for Incident Beam Position Sensing and Automatic Alignment

The spatial filter of a Si micromachined pinhole integrated with photodiodes is fabricated. The photodiode cells placed around the center pinhole can detect the relative position between the incident beam spot and the pinhole. The position signal obtained from a two or four cell type photodiode and position sensitive detector show the sensitivity even when the beam spot is near the center pinhole. Combined with the feedback control of the shape memory alloy actuator based on the obtained position signal, the pinhole is aligned automatically.     

Quantum effects for parametric X-ray radiation during channeling: Theory and first experimental observation

The theory of X-ray radiation from relativistic channeled electrons at the Bragg angles—parametric X-ray radiation (PXR) during channeling (PXRC)—is developed while accounting for two quantum effects: the initial population of bound states of transverse motion and the transverse “form-factor” of channeled electrons. An experiment was conducted using a 255 MeV electron beam from a linac at the SAGA Light Source. We have identified a difference in the angular distributions of PXR and PXRC and obtained a fairly good agreement between the theoretical and experimental results.     

Coherent X-ray radiation generated by a beam of relativistic electrons in a single crystal under conditions of multiple scattering

The dynamic theory of the coherent X-ray radiation of a divergent beam of relativistic electrons generated in a single-crystal wafer under conditions of the multiple scattering of incident particles is developed. Radiation cross sections are averaged over the divergent beam of rectilinear trajectories of electrons. Expressions describing the spectral-angular characteristics of parametric X-ray radiation and diffracted transition radiation under conditions of multiple scattering are obtained. Conditions under which the contribution of diffracted brehmsstrahlung can be disregarded are shown, and the spectral-angular characteristics of parametric X-ray radiation and diffracted transition radiation are calculated numerically for such conditions.     

Normal tracing deflectometry using a secondary light source

Scanning deflectometric profilers based on an f–gθ system are typical optical tools used to measure mirror profiles at many synchrotron facilities. Unlike these profilers, which are based on a pencil beam, here a secondary light source and a pinhole are used to construct a system that automatically selects a beam that will always pass through the pinhole and propagate along the normal direction of the measured area on the surface under test. By measuring the angle variation of the selected beam, slope variations of the surface under test can be measured. Systematic errors introduced by manufacturing defects or aberrations of an optical element, which greatly degrade the performance of traditional profilers, could be minimized by using the developed method. Simulation values of the proposed method and a conventional method are compared.     

Estimation of crystal sample structure by means of fast electron radiation

The dependence of the characteristics of X-ray radiation occurring under fast electron transmission through a crystal on a sample structure has been analyzed. A method to estimate the size of the crystal microblocks by means of the yield ratio of the parametric X-ray radiation and diffracted bremsstrahlung and transition radiation for different observation angles has been suggested. The possibility of estimating the dimension of the microblocks using the ratio of the intensities of these emission mechanisms for the same observation angle and several reflection orders has been discussed.     

Integral and temporal characteristics of soft X-rays of the PF-4 plasma focus setup

Soft X-rays of a setup with a power from 1.5 to 5 kJ, operating with argon, were measured using X-ray pinhole cameras and SPPD 11-04 detectors. Integral measurements of X-rays in energy ranges above 1.2, 1.5, 1.8, and 2.5 keV were performed using a 4-frame pinhole camera with hole sizes of ～250 µm. Simultaneously, the X-ray yield was measured with time resolution in the energy region of > 1.8 keV using a semiconductor detector. X-ray characteristics were experimentally studied at a capacitor bank voltage of 8–14 kV and argon pressures from 1.2 to 3 Torr. The size of hot points was estimated using the pinhole camera with a hole size of ～20 µm as less than 13–25 µm.     

蒙特卡罗模拟分析电子束发射度对照射量空间分布影响

加速器靶前正前方1 m处的照射量是衡量加速器光源辐射能力的重要物理参量。电子束轰击高原子序数靶产生的X射线空间分布具有很强的前冲性,照射量空间分布与电子束的发射度密切相关。采用高斯函数对不同电子束发射度条件下入射电子的空间分布和角度分布进行建模。应用蒙特卡罗方法对电子束打靶的轫致辐射过程进行模拟,分析电子束发射度对照射量的影响。同时还对整靶结构和叠靶结构下的轫致辐射光源照射量进行计算比较。结果表明,电子束的发散角是影响轫致辐射光源照射量的主要因素。与采用整靶结构相比,采用叠靶结构所获得的照射量空间分布基本一致,在正前方小角度范围内（0~4）的照射量有2%~3%的降低。     

一种聚焦型X射线探测器在轨性能标定方法

X射线探测器是X射线天文观测及脉冲星导航的核心器件,受发射振动、高能粒子辐射损伤及元器件老化等影响,X射线探测器空间观测性能会逐渐变化,X射线探测器在轨标定有利于观测天体X射线辐射信息的准确获取及精确建模.研究利用了脉冲星辐射能谱标定X射线探测器性能的方法,能较好地消除探测器本底及空间环境噪声的影响,通过处理脉冲星导航试验卫星(XPNAV-1卫星)的Crab脉冲星观测数据,评估了我国首款聚焦型X射线探测器的在轨性能.计算结果表明,XPNAV-1卫星上聚焦型X射线探测器的有效面积在0.6-1.9 keV能段内优于2 cm~2,其中在0.7 keV能量处取得最大值3.06 cm~2,探测效率约10%;有效面积随着探测能量增大而减小,在2—3.5 keV能段内有效面积约为1 cm~2,而大于5 keV能段的有效面积约为0.1 cm~2,且此能段估计精度明显受光子统计误差影响.同时研究了考虑能量响应矩阵的探测器有效面积标定新方法,利用地面性能测试中五个特征能谱处的能量分辨率重构其能量响应矩阵,重新标定了聚焦型X射线探测器有效面积,发现该能量响应矩阵对结果影响较小.最后建议观测某些超新星遗迹监测能量分辨率及能量线性等指标的变化.     

Beam distribution reconstruction simulation for electron beam probe

An electron beam probe(EBP) is a detector which makes use of a low-intensity and low-energy electron beam to measure the transverse profile, bunch shape, beam neutralization and beam wake field of an intense beam with small dimensions. While it can be applied to many aspects, we limit our analysis to beam distribution reconstruction.This kind of detector is almost non-interceptive for all of the beam and does not disturb the machine environment.In this paper, we present the theoretical aspects behind this technique for beam distribution measurement and some simulation results of the detector involved. First, a method to obtain a parallel electron beam is introduced and a simulation code is developed. An EBP as a profile monitor for dense beams is then simulated using the fast scan method for various target beam profiles, including KV distribution, waterbag distribution, parabolic distribution,Gaussian distribution and halo distribution. Profile reconstruction from the deflected electron beam trajectory is implemented and compared with the actual profile, and the expected agreement is achieved. Furthermore, as well as fast scan, a slow scan, i.e. step-by-step scan, is considered, which lowers the requirement for hardware, i.e. Radio Frequency deflector. We calculate the three-dimensional electric field of a Gaussian distribution and simulate the electron motion in this field. In addition, a fast scan along the target beam direction and slow scan across the beam are also presented, and can provide a measurement of longitudinal distribution as well as transverse profile simultaneously. As an example, simulation results for the China Accelerator Driven Sub-critical System(CADS) and High Intensity Heavy Ion Accelerator Facility(HIAF) are given. Finally, a potential system design for an EBP is described.     

Panoramic measurements of electron beam densities by Thomson scattering of laser radiation

The possibility of using a panoramic detector with a television signal-recording system in an apparatus to observe Thomson scattering of laser radiation by a nonrelativistic electron beam is discussed. Panoramas of Thomson and Rayleigh scattering and of the electron beam luminescence are presented. Estimates are given of the sensitivity and spatial resolution of the apparatus. Results of panoramic and single-point methods of investigation are compared. Possibilities for extending the range of the Thomson scattering method to measure the density distribution in nonrelativstic electron beams are discussed. Zh. Tekh. Fiz. 69, 80–83 (June 1999)