Measurement of impurity lines with two- crystal x-ray spectrometers on EAST

To simultaneously measure the He-like and H-like argon spectra, a two-crystal assembly has been deployed to replace the previous single crystal on the tangential x-ray crystal spectrometer. By selecting appropriate crystals with similar Bragg angles, plasma temperature in the range of 0.5 keV≦ T_e≦ 10 keV and rotation can be diagnosed based on the He-like and H-like argon spectra. However, due to the added complexity in the two-crystal assembly in which the spectra might be diffracted by two crystals, some additional impurity lines were identified. For example, tungsten (W) lines in different ionization states were diffracted by the He-like and H-like crystal. Additional molybdenum (Mo) lines in the wavelength range of He-like and H-like argon spectra lines were also summarized. The existence of these additional lines caused the fitted temperature to be different from the true values. This paper presents the identified lines through a comparison with available database, which should be included in the fitting procedure.     

Chemical shift measurements of PIXE spectra using a position-sensitive crystal spectrometer

The in-air high-resolution PIXE system composed of a flat analyzing crystal and a position-sensitive proportional counter was applied to measure line shifts of Si K and P K X-rays from various samples induced by an external proton beam. Line shifts that reflect chemical environments of atoms in target samples were determined with the precision of 0.1 eV. The utility of the method for chemical state analysis of minor elements down to the order of 0.1% was demonstrated.     

Space-resolved vacuum-ultraviolet spectroscopy for measuring impurity emission from divertor region of EAST tokamak

The measurement of impurity distribution in the divertor region of tokamaks is key to studying edge impurity transport. Therefore, a space-resolved vacuum-ultraviolet (VUV) spectrometer is designed to measure impurity emission in the divertor region on EAST. For good spectral resolution, an eagle-type VUV spectrometer with 1 m long focal length with spherical holograph grating is used in the system. For light collection, a collimating mirror is installed between the EAST plasma and the VUV spectrometer to extend the observing range to cover the upper divertor region. Two types of detectors, i.e. a back-illuminated charge-coupled device detector and a photomultiplier-tube detector, are adopted for the spectral measurement and high-frequency intensity measurement for feedback control, respectively. The angle between the entrance and exit optical axis is fixed at 15°. The detector can be moved along the exit axis to maintain a good focusing position when the wavelength is scanned by rotating the grating. The profile of impurity emissions is projected through the space-resolved slit, which is set horizontally. The spectrometer is equipped with two gratings with 2400 grooves/mm and 2160 grooves/mm, respectively. The overall aberration of the system is reduced by accurate detector positioning. As a result, the total spectral broadening can be reduced to about 0.013 nm. The simulated performance of the system is found to satisfy the requirement of measurement of impurity emissions from the divertor area of the EAST tokamak.     

Simulation studies of tungsten impurity behaviors during neon impurity seeding with tungsten bundled charge state model using SOLPS-ITER on EAST

An investigation into tungsten (W) impurity behaviors with the update of the EAST lower W divertor for H-mode has been carried out using SOLPS-ITER. This work aims to study the effect of external neon (Ne) impurity seeding on W impurity sputtering with the bundled charge state model. As the Ne seeding rate increases, plasma parameters, W concentration (), and eroded W flux () at both targets are compared and analyzed between the highly resolved bundled model 'jett' and the full W charge state model. The results indicate that 'jett' can produce divertor behaviors essentially in agreement with the full W charge state model. The bundled scheme with high resolution in low W charge states (20+) has no obvious effect on the Ne impurity distribution and thus little effect on W sputtering by Ne. Meanwhile, parametric scans of radial particle and thermal transport diffusivities (and) in the SOL are simulated using the 'jett' bundled model. The results indicate that the transport diffusivity variations have significant influences on the divertor parameters, especially for W impurity sputtering.     

Chemical effects in the Kβ X-ray emission spectra of sulfur

In this work our previous study about chemical effects in the K spectra of S compounds employing high-resolution X-ray spectroscopy has been extended to the Kβ emission spectra. The measurements were performed with a wavelength dispersive single crystal spectrometer operated in the von Hamos geometry having an energy resolution comparable to the natural linewidth of the measured Kβ X-ray lines. The target fluorescence was produced by irradiating the samples with the bremsstrahlung from an X-ray tube. The energies and widths of the main components in the Kβ emission spectrum are given for different sulfur compounds (sulfide, sulfite, sulfate). The measured energy shifts between the Kβ lines of the compounds and elemental sulfur are presented as a function of the sulfur oxidation state and compared with the results obtained from the former K measurements.     

Spatially-resolved flat-field soft X-ray spectrometer on experimental advanced superconducting tokamak

A space- and time-resolved flat-field soft X-ray spectrometer with the wavelength range of 1–13 nm has been developed to study impurity behavior on the Experimental Advanced Superconducting Tokamak (EAST). Using an entrance slit, a varied line spacing grating (2400 grooves/mm at the grating center), and a charged coupled device (CCD) system, time evolution of profiles of impurity line emissions were recorded. The spectral resolution of the spectrometer is 0.006 nm at 5 nm when the width of entrance slit is set at 0.03 mm. The best spatial resolution obtained is 24.5 mm with the height of slit at 1.0 mm. The spectrometer is placed 8000 mm away from the plasma center and the observed spatial range covers 0–450 mm from the equatorial plane of EAST. The first experimental results were obtained from the recent EAST campaign. The system was shown to be capable of observing spectral lines from both intrinsic low-Z impurities (C, O, et al.) and highly ionized medium- and high-Z impurities (Fe, Cr, Ni, Cu, et al.). Spectral lines from the full wavelength range (1–13 nm) can be obtained by moving the position of the CCD. Spectra with the wavelength intervals of 1–2 nm show strong metal lines for H-mode discharges. Time evolutions of C VI (3.373 nm) and O VIII (1.897 nm) lines are presented and detail analysis is performed combining electron density intensity, D_α and soft X-ray and extreme ultraviolet (XUV) radiation intensities. Evolutions of profiles of C VI (3.373 nm) and O VIII (1.897 nm) at core plasma were also shown, indicating that the spectrometer can be applied for impurity transport studies,     

用于激光等离子体诊断的滤波-差分硬X光谱仪

介绍了利用滤片和Si导体探测器差分阵列组合的硬X光谱仪的工作原理、结构性能和测谱特点。给出ICF实验考核结果。     

Observation of Central Toroidal Rotation Induced by ICRF on EAST

Core plasma rotation of both L-mode and H-mode discharges with ion cyclotron range of frequency(ICRF) minority heating(MH) scheme was measured with a tangential X-ray imaging crystal spectrometer on EAST(Experimental Advanced Superconducting Tokamak).Cocurrent central impurity toroidal rotation change was observed in ICRF-heated L-and H-mode plasmas.Rotation increment as high as 30 km/s was generated at ~1.7 MW ICRF power.Scaling results showed similar trend as the Rice scaling but with significant scattering,especially in L-mode plasmas.We varied the plasma current,toroidal field and magnetic configuration individually to study their effect on L-mode plasma rotation,while keeping the other major plasma parameters and heating unchanged during the scanning.It was found that larger plasma current could induce plasma rotation more efficiently.A scan of the toroidal magnetic field indicated that the largest rotation was obtained for on-axis ICRF heating.A comparison between lower-single-null(LSN)and double-null(DN) configurations showed that LSN discharges rendered a larger rotation change for the same power input and plasma parameters.     

The influence of calculated CT X-ray spectra on organ absorbed dose to a human phantom

We have evaluated the utilization of five X-ray spectra codes for Monte Carlo (MC) simulations of computed tomography (CT) examinations. Four codes (Xcomp5r, X-raytbc, X-rayb&m and Srs-78) are semi-empiricals and one is based on MC methods (EGSnrc/BEAM Monte Carlo code). The X-ray spectra calculated by the semi-empirical codes were compared with the X-ray spectrum calculated by the EGSnrc/BEAM MC code. The absorbed doses to each organ or tissue were also compared. The calculated doses, and its respective organs, for which occurs the greatest disagreement, as well as the calculated doses for the testes and red bone marrow (two important organs used for calculating effective dose) were presented. The results obtained in this work are in good agreement with those obtained by Ay [M.R. Ay, S. Sarkar, M. Shahriari, D. Sardari, H. Zaidi, Assessment of different computational models for generation of X-ray spectra in diagnostic radiology and mammography, Med. Phys. 32 (2005) 1660], mainly for the bremsstrahlung distribution. Also, it was noted that the total characteristic X-rays produced by the EGSnrc/BEAM MC code increases with the increase of voltage more intensely than with the Xcomp5r, X-raytbc and Srs-78 codes. Comparison between the absorbed dose to each organ or tissue showed that, for X-ray spectra with additional filtration, the code based on Tucker et al. is in agreement with EGSnrc/BEAM MC code. But, for X-ray spectra without additional filtration the code based on Tucker et al. model presented the strong disagreement with EGSnrc/BEAM MC code.     

用同步辐射X射线荧光微区分析技术测定单晶硅中的掺杂元素As

利用同步辐射Ｘ射线微区分析技术，研究了单晶硅中掺杂元素Ａｓ浓度的定量分布，并对结果进行了讨论。     

Line identification of extreme ultraviolet(EUV) spectra from low-Z impurity ions in EAST tokamak plasmas

Extreme ultraviolet(EUV) spectra emitted from low-Z impurity ions in the wavelength range of10–500 ? were observed in Experimental Advanced Superconducting Tokamak(EAST)discharges. Several spectral lines from K-and L-shell partially ionized ions were successfully observed with sufficient spectral intensities and resolutions for helium, lithium, boron, carbon,oxygen, neon, silicon and argon using two fast-time-response EUV spectrometers of which the spectral intensities are absolutely calibrated based on the intensity comparison method between visible and EUV bremsstrahlung continua. The wavelength is carefully calibrated using wellknown spectra. The lithium, boron and silicon are individually introduced for the wall coating of the EAST vacuum vessel to suppress mainly the hydrogen and oxygen influxes from the vacuum wall, while the carbon and oxygen intrinsically exist in the plasma. The helium is frequently used as the working gas as well as the deuterium. The neon and argon are also often used for the radiation cooling of edge plasma to reduce the heat flux onto the divertor plate. The measured spectra were analyzed mainly based on the database of National Institute of Standards and Technology. As a result, spectral lines of He Ⅱ, Li Ⅱ–Ⅲ, B Ⅳ–Ⅴ, C Ⅲ–Ⅵ, O Ⅲ–Ⅷ, Ne Ⅱ–Ⅹ,Si Ⅴ–Ⅻ, and Ar Ⅹ–XVI are identified in EAST plasmas of which the central electron temperature and chord-averaged electron density range in T_(e0)=0.6–2.8 keV and n_e=(0.5–6.0)×10~(19) m~(-3), respectively. The wavelengths and transitions of EUV lines identified here are summarized and listed in a table for each impurity species as the database for EUV spectroscopy using fusion plasmas.     

Thermal analysis on the EAST tungsten plasma facing components with shaping structure counteracting the misalignment issues

Tungsten monoblock type tiles with ITER dimensions along with supporting cassette components were installed at EAST's upper diverter during 2014 and EAST's lower diverter will also be upgraded in the future.These cassette structures pose critical issues on the high cumulative incident heat flux due to the leading edges and misalignments(0 ~ 1.5 mm),which may result in the destruction or even melting of the tungsten tile.The present work summarizes the thermal analysis using ANSYS multiphysics software 15.0 performed on the actively cooled W tiles to evaluate the shaping effect on surface temperature.In the current heat flux conditions(Q_Ⅱ ~ 100 MW m~(-2)),the adopted chamfer shaping(1×1 mm) can only reduce the maximum temperature by about 14%,but it also has a melting risk at the maximum misalignment of1.5 mm.The candidate shaping solutions elliptical(round) edge,dome and fish-scale are analyzed for comparison and are identified not as good as the dual chamfer structure.A relatively good dual chamfer(2×13 mm) shaping forming a symmetrical sloping roof structure can effectively counteract the 1.5 mm misalignment,reducing the maximum temperature by up to50%.However,in the future heat flux conditions(Q_Ⅱ ~ 287 MW m~(-2)),it may only endure about0.5 mm misalignment.Moreover,no proper shaping solution has been found that can avoid melting at the maximum misalignment of 1.5 mm.Thus,the engineering misalignment has to be limited to an acceptable level.     

用于ICF软X光能谱仪时标系统的功分器研制

在ICF软X光能谱仪诊断实验中,为了将能谱仪各通道输出的纳秒尺度测量信号在时间上精确关联,需要测试系统提供定时精度好于200ps多路一致的时标信号.为此研制了无源纯电阻8路功分器来提供时标信号,通过对其性能进行的测试,表明该功分器基本满足现有物理实验要求.同时对功分器的进一步改进进行了分析,提出了解决方案.     

一种基于SiPM的具有高能量分辨率的紧凑型溴化镧γ谱仪

基于光电倍增管(photomultiplier tube,简称PMT)的LaBr₃:Ceγ谱仪具有比Na I(Tl)γ谱仪更高的能量分辨率,但具有体积大、对磁场敏感、需要高电压等缺点。硅光电倍增管(Silicon photomultiplier tube,简称Si PM)具有与PMT相近的增益和效率,同时具有诸如高定时分辨率、抗磁场能力强、低偏压和紧凑尺寸等优良特性。本文将LaBr₃:Ce晶体与SiPM阵列耦合,设计研制基于Si PM的紧凑型LaBr₃:Ceγ谱仪,通过降噪、优化工作电压等措施改善SiPM的缺点对γ谱仪性能的影响。工作电压的噪声会导致能量分辨率发生恶化,通过设计无源滤波电路CLCπ型滤波器,利用其对直/交流阻抗的不同特性,滤除高频纹波,工作电压的信噪比从未降噪前的62.6 d B提高到74.64 dB;能量分辨率最优值对应于表示暗噪声、串扰、光电探测效率和SiPM增益之间折衷的最佳工作电压。通过实验给出不同工作电压下的能量分辨率,确定最佳工作电压为54.8 V,该电压下的能量分辨率为3.06%(@662 ...     

BaF2正电子寿命谱仪时间分辨率的改进

介绍了不同材料,不同形状的封装对BaF2晶体光收集的影响。使用聚四氟乙烯薄膜对BaF2晶体作伞状封装,光收集效果较好,在此条件下,常规正电子湮灭寿命谱仪的时间分辨率在^22Na能窗下达到180ps。     

吸收法在强激光与固体靶所致脉冲X射线能谱测量中的研究进展北大核心CSCD

脉冲X射线能谱测量,对于强激光装置中的物理诊断以及辐射防护具有重要意义。脉冲X射线具有脉冲时间短、注量大、能谱范围宽等特点,常规脉冲测量技术往往受到探测器死时间、堆积效应的限制而无法适用。目前多个国家都建立了强激光装置的研究平台,并开展X射线能谱测量相关研究。本文首先介绍了基于吸收法原理且适用于中低能脉冲X射线的测量方法:Ross Pair法和衰减法。然后针对这两种方法从5个方面(探测器结构、滤片材料、探测介质选择、散射控制以及解谱方法)综述了脉冲X射线吸收谱仪的研究进展,并分析了各自的适用性。目前激光装置中脉冲X射线能谱的测量还面临着能量分辨率不理想、结果不确定度无法量化和被动式能谱测量操作不便等问题。随着激光装置的不断升级,脉冲X射线注量以及打靶频次将不断增加,对探测器的耐辐照性能以及响应速度提出了更高的要求。     

Design of a multi-voltage probe system forICRF antenna coupling resistancemeasurement on EAST

A multi-voltage probe array system is designed to measure the coupling resistance of an ioncyclotron resonance frequency antenna. In the process of the antenna coupling resistance dataextraction, the minimization algorithm, the original Levenberg–Marquardt algorithm, is replacedby the Broyden–Fletcher–Goldfarb–Shanno algorithm to achieve more stable and accurateresults. Moreover, a simple model of the multi-voltage probe array was applied to simulate theperformance of the Kalman filter, and to optimize the distance and position of the probes andprobe number to mitigate the influence of the system noise on the rebuilt results. During theEAST experiment in 2019, a four-voltage probe array was applied to measure the couplingresistance of line 6 during high confined mode discharge. The measurement results by the multi-voltage probe array system and the voltage/current probe pair show a good agreement.     

Present Status of the Electron Cyclotron Emission Measurements on HT-7 and EAST

Present status of the diagnostics for electron cyclotron emission measurements on both HT-7 and EAST is reported. A 16-channel heterodyne radiometer system and a 20-channel grating polychromator, have been installed on HT-7 and EAST. A 32-channel heterodyne ra- diometer system, with a wider frequency coverage and better spatial resolution, is being built. In order to provide a reliable electron temperature profi, an in-situ absolute calibration system is currently being built. With the ECE measurements, study on the electron heat transport and the anomalous Doppler resonance is conducted.     

Observation and characterization of the effect of electron cyclotron waves on toroidal rotation in EAST L-mode discharges

The change in the toroidal rotation of plasma caused by electron cyclotron wave (ECW) injection has been observed in EAST.It is found that the response of the rotation is similar for all possible ECW toroidal injection angles.The core toroidal rotation velocity increases in the co-current direction along with a rise in the plasma temperature and stored energy.The profile of the electron temperature,ion temperature and toroidal rotation velocity gradually become peaked.The change in toroidal rotation in the core increases with the ECW injection power.Different behavior is observed when the ECWs are injected into low hybrid current drive (LHCD) target plasmas,where the electron temperature and rotation profile become peaked,while the ion temperature profile flattens after ECW injection,suggesting different transport characteristics in energy and momentum.     

Readout electronics for a high-resolution soft X-ray spectrometer based on silicon drift detector

The readout electronics for a prototype soft X-ray spectrometer based on silicon drift detector (SDD),for precisely measuring the energy and arrival time of X-ray photons is presented in this paper.The system mainly consists of two parts,i.e.,an analog electronics section (including a pre-amplifier,a signal shaper and filter,a constant fraction timing circuit,and a peak hold circuit) and a digital electronics section (including an ADC and a TDC).Test results with X-ray sources show that an energy dynamic range of 1-10 keV with an integral nonlinearity of less than 0.1％ can be achieved,and the energy resolution is better than 160 eV@5.9 keV FWHM.Using a waveform generator,test results also indicate that time resolution of the electronics system is about 3.7 ns,which is much less than the transit time spread of SDD (＜100 ns) and satisfies the requirements of future applications.