Soft X-ray Imaging System Research Articles

Development of a toroidal soft x-ray imaging system and application for investigating three-dimensional plasma on J-TEXT

A toroidal soft x-ray imaging (T-SXRI) system has been developed to investigate three-dimensional (3D) plasma physics on J-TEXT. This T-SXRI system consists of three sets of SXR arrays. Two sets are newly developed and located on the vacuum chamber wall at toroidal positions of ° and °, respectively, while one set was established previously at °. Each set of SXR arrays consists of three arrays viewing the plasma poloidally, and hence can be used separately to obtain SXR images via the tomographic method. The sawtooth precursor oscillations are measured by T-SXRI, and the corresponding images of perturbative SXR signals are successfully reconstructed at these three toroidal positions, hence providing measurement of the 3D structure of precursor oscillations. The observed 3D structure is consistent with the helical structure of the m/n = 1/1 mode. The experimental observation confirms that the T-SXRI system is able to observe 3D structures in the J-TEXT plasma.

Non-Destructive Method for Estimating Seed Weights from Intact Peanut Pods Using Soft X-ray Imaging

In the U.S., peanut farmers receive premium prices for crops with high seed grades. One component of seed grade is the proportion of seed weight to that of pod hulls and other matter. Seed weight and size are also important traits for food processors. Current methods for evaluating peanut seed grade require the opening of the pod and are time-consuming and labor-intensive. In this study, a non-destructive and efficient method to determine peanut seed weights was investigated. X-ray images of a total of 513 peanut pods from three commercial cultivars, each representing three market types, were taken using a soft X-ray imaging system. The region of interest of each image, the seeds, was extracted two ways, manually and with a differential evolution segmentation algorithm. The comprehensive attenuation index (CAI) value was calculated from the segmented regions of interest. Lastly, linear regression models were established between peanut seed weights and the CAI. The results demonstrated that the X-ray imaging technology, coupled with the differential evolution segmentation algorithm, may be used to estimate seed weights efficiently from intact peanut pods.

Soft X-Ray Imaging of Polymer Electrolyte Fuel Cells Using Different Support Materials for Catalyst Layers

The polymer electrolyte fuel cell (PEFC) is a highly efficient and environmentally friendly energy device that has been developed for fuel cell vehicles and other applications due to its low operating temperature and compact size. The PEFC is assembled by putting a membrane electrode assembly (MEA), which consists of the polymer electrolyte membrane with the catalyst layers and the gas diffusion layers on both sides, between separators. Pt nanoparticle catalysts supported on carbon black (Pt/C) are usually used for catalyst layers because of their large surface area and high electrical conductivity. However, carbon supports are oxidized and corroded during operation, resulting in performance degradation. Therefore, research has been conducted using Pt supported on tin oxide (Pt/Nb-SnO2), which has high durability and a porous structure similar to that of carbon supports, as an alternative material for the catalyst layers [1]. Tin oxide supports have material properties such as wettability that differ greatly from carbon supports, and the effect of these material properties on liquid water behavior during power generation has not been clarified. It is essential to understand the liquid water transport in PEFCs for the improvement of performance, because excessive liquid water accumulation (flooding) at the cathode hinders the transport of the reaction gas and causes concentration overvoltage.In this study, in order to clarify the effect of the catalyst layer support material on the liquid water transport, we made catalyst layers using carbon and tin oxide supports respectively, and investigated the liquid water behavior in the MEAs under fuel cell operation using high-resolution soft X-ray radiography.PEFCs with a reaction area of 5×8 mm2 were constructed using carbon support catalyst layers and tin oxide support catalyst layers, respectively. The same components were used except for the catalyst layer. The PEFCs were set in a soft X-ray imaging system (TUX-9000D, Mars-Tohken X-ray Inspection). This system can observe PEFCs and take images at a spatial resolution of about 1.0 µm. Hydrogen was supplied to the anode and air to the cathode, and the power generation tests were conducted in the high current density region where flooding is likely to occur. The voltage drop during power generation of the PEFC with Pt/SnO2 catalyst layer was larger than that of the PEFC with Pt/C catalyst layer. In-situ observation of the liquid water behavior in the PEFC was performed by taking images in the MEA cross-sectional direction at the same time as power generation. The images were taken at the position where both the area under the rib and the area under the channel could be observed. The soft X-ray radiograph of the MEA before power generation is shown in Figure 1 (a). The generated water during the power generation was identified by image processing that subtracted the image taken after operation from the image taken under open-circuit voltage conditions. Figure 1 (b) and (c) show the soft X-ray radiographs of liquid water after 20 minutes of power generation under the current density of 0.8 A/cm2. After the cell startup, the amount of water retention increases on the cathode side of the PEFC and the difference in the amount of water retention under the rib and under the channel was observed. It was also shown that the distribution of liquid water in the porous material was different between the carbon support and tin oxide support catalyst layers attributed to support materials and structures of the catalyst layers properties.AcknowledgmentsThe catalyst with Tin oxide support material used in this study was provided by NEDO ECCEED'30. The authors would like to acknowledge their assistance in assembling PEFCs for visualization study.[1] Y. Chino et al, J Electrochem Soc., 162-7 (2015), F736. Figure 1

Characterization of Agglomerated Particles in a PEFC Electrode Slurry by Soft X-Ray Radiography

Polymer electrolyte fuel cells (PEFCs) have been commercialized for various applications, such as automobiles and household power sources, because of their low operating temperature and high power density. A PEFC comprises a polymer electrolyte membrane as the electrolyte and electrodes consisting of a catalyst layer and a gas diffusion layer. The catalyst layer plays a role as an electrochemical reaction field with a porous structure and is generally prepared by mixing platinum-supported carbon and ionomer in a solvent to make a suspension (electrode slurry), which is then coated on a substrate and dried. Mixed particles aggregate in the electrode slurry, which affects the porous structure of the catalyst layer. In order to improve the cell performance of PEFCs by controlling the structure of catalyst layers, it is necessary to understand and characterize the electrode slurry [1-2].In this study, we carried out a temporal visualization of the electrode slurry by a soft X-ray radiography system (Mars-Tohken X-ray Inspection, TUX-9000D) to clarify the agglomeration/dispersion state and migration phenomena of particles in the electrode slurry. PEFC electrode slurry is a black opaque suspension and its structure is hardly probed by visible light. In order to observe the electrode slurry by soft X-ray radiography, we used a house-made PTFE container. The container was placed on the sample stage of the soft X-ray imaging system for observation. In order to investigate the effect of interaction between particles, four types of electrode slurries with different non-volatile ratios (7.0, 0.70, 0.40, and 0.11%) were prepared for observation. The ionomer-to-carbon ratio of all electrode slurries was kept at 1.0. The dispersions were prepared by a planetary centrifugal mixer for 30 minutes (2000 rpm for the revolution and 800 rpm for the rotation) just before soft X-ray visualization.Figure 1 shows a soft X-ray radiograph of electrode slurry (non-volatile ratio: 7.0%). The image captured a spatial variation of X-ray absorption in the electrode slurry. High X-ray absorption regions correspond to high density in the slurry, attributed to agglomerates of platinum-supported carbon particles and ionomers. Their diameters were about 10 – 40 μm, and less variation was found in the non-volatile ratio of the electrode slurry from 0.11 to 7.0%. However, the number of agglomerated particles varied depending on the non-volatile ratio of the electrode slurry. The less the non-volatile ratio, the less the number of agglomerated particles observed, suggesting that migrations in the electrode slurry were much affected by the non-volatile component in the slurry. We performed a time-series visualization of the electrode slurry placed in the X-ray radiography system for several hours. Sedimentation behaviors of the agglomerated particles were observed in all electrode slurries. The captured images were processed to quantitatively characterize sedimentation rates in the slurry. It was found that the less the non-volatile ratio, the more the sedimentation rate of the agglomerated particles.AcknowledgmentsThis work was supported by JSPS KAKENHI Grant Number 18K13702 and 21H04540.[1] T. Suzuki et al., ECS Trans., 86-13 (2018), 193.[2] S. Khandavalli et al., ACS Appl. Mater. Interfaces, 10 (2018), 43610. Figure 1

Soft x-ray imaging system used for Z-pinch experiments

基于塑料闪烁体转换和光学条纹相机的方法建立了一套用于Z箍缩实验中的软X射线条纹图像诊断系统, 解决了以往实验中使用的X射线条纹相机易被电磁环境干扰以及相机电极部件易被实验产生的高速粒子损伤的问题. 诊断系统的光谱响应范围主要集中在0.2—10 keV, 系统的空间分辨率经过理论评估小于120 μm, 通过标定闪烁体对X射线的时间响应特性给出了系统的时间分辨率约为1 ns. 诊断系统拍摄到了铝丝阵内爆等离子体的一维空间和时间分辨的X射线条纹图像, 给出了等离子体的内爆一致性和辐射均匀性等特征信息.

Magnetohydrodynamics-induced internal crash near density limit in ohmic discharge on experimental advanced superconducting tokamak

The magnetohydrodynamics (MHD)-induced internal crash (IC) is one of the most fundamental dynamics of a tokamak discharge. Study of IC and the consequent formation of seed island (for neo-classical tearing modes) are still attractive in both experimental and numerical studies. In this work, a set of MHD-induced sawtooth like crashes (SLCs) have been observed in experimental advanced superconducting tokamak (EAST) ohmic discharge near density limit. With the tomography of high-resolution upgraded soft x-ray imaging system, it is observed that m/n = 2/1 tearing mode converts to a m/n = 1/1 instability, and it then triggers crash in the plasma core, here, m is the poloidal mode number and n is the toroidal mode number. Similar to sawtooth crash (SC), the crash of SLC here is due to m/n = 1/1 mode nonlinear dynamic. An extended MHD simulation code M3D is used to understand of the dynamics of m/n = 1/1 internal kink mode in SC in torus. A complex SC is reproduced from M3D nonlinear simulation under EAST realistic magnetic flux equilibrium and experimental resistivity. The rapid growth of unstable m/n = 1/1 kink and interaction with its higher harmonics, are responsible for SC. The simulation results show an existence of annular chaos belt outside q = 1 surface during SC. Furthermore, magnetic islands with higher poloidal mode number are found after SC. The formation of island after SC make plasma current profile flat in the core.

Single-shot achromatic imaging for broadband soft x-ray pulses

An achromatic soft x-ray imaging system based on a transmission microscope equipped with a pair of Wolter mirrors was constructed. The two Wolter mirrors for the condenser and the objective were fabricated precisely by using an electroforming replication process. The samples were illuminated by broadband high harmonic pulses in the wavelength range of 26 nm to 35 nm via the condenser mirror, and transmission bright-field images without chromatic aberration were formed by the objective mirror. A single-shot image illuminated by a femtosecond laser pulse was recorded at a spatial resolution of about 200 nm. The fundamental capability of the microscope to realize broadband images without chromatic aberration will lead to the development of soft x-ray microscopes with extremely short illumination pulses on the order of attoseconds.

Fast Tangentially Viewed Soft X-Ray Imaging System Based on Image Intensifier with Microchannel Plate Detector on QUEST

Fast Tangentially Viewed Soft X-Ray Imaging System Based on Image Intensifier with Microchannel Plate Detector on QUEST

In-orbit performance of the soft X-ray imaging system aboard Hitomi (ASTRO-H)

Abstract We describe the in-orbit performance of the soft X-ray imaging system consisting of the Soft X-ray Telescope and the Soft X-ray Imager aboard Hitomi. Verification and calibration of imaging and spectroscopic performance are carried out, making the best use of the limited data of less than three weeks. Basic performance, including a large field of view of ${38^{\prime }}$ × ${38^{\prime }}$, is verified with the first-light image of the Perseus cluster of galaxies. Amongst the small number of observed targets, the on-minus-off pulse image for the out-of-time events of the Crab pulsar enables us to measure the half-power diameter of the telescope as ∼${1 {^{\prime}_{.}} 3}$. The average energy resolution measured with the onboard calibration source events at 5.89 keV is 179 ± 3 eV in full width at half maximum. Light leak and crosstalk issues affected the effective exposure time and the effective area, respectively, because all the observations were performed before optimizing an observation schedule and the parameters for the dark-level calculation. Screening the data affected by these two issues, we measure the background level to be 5.6 × 10−6 counts s−1 arcmin−2 cm−2 in the energy band of 5–12 keV, which is seven times lower than that of the Suzaku XIS-BI.

Regularization of soft-X-ray imaging in the DIII-D tokamak

An image inversion scheme for the soft-X-ray imaging system (SXRIS) diagnostic at the DIII-D tokamak is developed to obtain the local soft-X-ray emission at a poloidal cross-section from the spatially line-integrated image taken by the SXRIS camera. The scheme uses the Tikhonov regularization method since the inversion problem is generally ill-posed. The regularization technique uses the generalized singular value decomposition (GSVD) to determine a solution that depends on a free regularization parameter. The latter has to be chosen carefully, and the so-called L-curve method to find the optimum regularization parameter is outlined. A representative test image is used to study the properties of the inversion scheme with respect to inversion accuracy, amount/strength of regularization, image noise and image resolution. The optimum inversion parameters are identified, while the L-curve method successfully computes the optimum regularization parameter. Noise is found to be the most limiting issue, but sufficient regularization is still possible at noise to signal ratios up to 10%–15%. Finally, the inversion scheme is applied to measured SXRIS data and the line-integrated SXRIS image is successfully inverted.

Design of the high-resolution soft X-ray imaging system on the Joint Texas Experimental Tokamak.

A new soft X-ray diagnostic system has been designed on the Joint Texas Experimental Tokamak (J-TEXT) aiming to observe and survey the magnetohydrodynamic (MHD) activities. The system consists of five cameras located at the same toroidal position. Each camera has 16 photodiode elements. Three imaging cameras view the internal plasma region (r/a < 0.7) with a spatial resolution about 2 cm. By tomographic method, heat transport outside from the 1/1 mode X-point during the sawtooth collapse is found. The other two cameras with a higher spatial resolution 1 cm are designed for monitoring local MHD activities respectively in plasma core and boundary.

Design and Initial Result of Time-Resolved Vertical Soft X-Ray Imaging System in Low-&lt;i&gt;A &lt;/i&gt;RFP

A time-resolved vertical soft X-ray (SXR) imaging system was constructed. To identify the structure of the magnetic island using the obtained SXR images, we calculated the two-dimensional (2-D) image expected from low-aspect-ratio (low-A) reversed field pinch (RFP) plasmas. The 2-D image was found to reflect the change in the radiation power caused by the magnetic island. A preliminary experimental result in which we observed vertical SXR images from the quasi-periodic quasi-single helicity (QSH) state in low-A RFP plasmas is presented. We successfully obtained the time evolution of SXR images from the vertical port. By comparing the observed images with simulated images, we found that the evolution of the experimental SXR image suggests a rotating helical configuration.

Closed-form representations for third-order aberrations of two-aspherical mirror aplanats with the mirror tilt and decenter

Approximate equations are derived for imaging aberrations of two-aspherical-mirror aplanats for soft X-ray imaging. These expressions include the Seidel terms for unperturbed states and the axial coma resulting from the tilt and decenter of the mirror surface. A simple analytical method for reducing both the Seidel terms and the axial coma enables us to design novel soft X-ray imaging systems utilizing a wide field of view with reduced sensitivity to mirror misalignments. The method is illustrated by applying it to a two-mirror system for soft X-ray microscopy with a magnification m =−1/50. The design example showed an appreciable reduction in sensitivity, as compared with the existing anastigmatic designs that include a standard Schwarzschild configuration. Imaging aberrations of the novel system are also confirmed by a numerical ray tracing method.

Soft X-Ray Imaging Design and Analysis Methods on DIII-D

A new tangential 2D Soft X-Ray Imaging System (SXRIS) is being designed to examine the edge magnetic island structure in the lower X-point region of DIII-D. A synthetic diagnostic calculation coupled to 3D emissivity estimates is used to generate phantom images. Phillips-Tikhonov regularization is used to invert the phantom images for comparison to the original emissivity model. Noise level, island size, and equilibrium accuracy are scanned to assess the feasibility of detecting edge island structures. Models of typical DIII-D discharges indicate integration times > 1 ms with accurate equilibrium reconstruction are needed for small island (< 3 cm) detection.

Initial Result of Successive SXR Imaging Measurement in Low-A RFP

A fast successive soft-X ray (SXR) imaging system where SXR camera and high-speed camera for the study of time evolution of magnetic islands has been constructed. A preliminary experimental result in which we observed tangential SXR images from quasi-periodic quasi-single helicity (QSH) state in low-aspect-ratio (low-A) reversed field pinch (RFP) is presented. We successfully obtained time evolution of SXR images from tangential port. By comparison obtained images with simulated images, we may conclude that the evolution of experimental SXR image suggests the rotating QSH RFP configuration. The filamentous configuration tends to be observed in QSH state rather than in multi-helicity (MH) state.

2D soft x-ray system on DIII-D for imaging the magnetic topology in the pedestal region

A new tangential two-dimensional soft x-ray imaging system (SXRIS) is being designed to examine the edge island structure in the lower X-point region of DIII-D. Plasma shielding and/or amplification of the calculated vacuum islands may play a role in the suppression of edge-localized modes via resonant magnetic perturbations (RMPs). The SXRIS is intended to improve the understanding of three-dimensional (3D) phenomena associated with RMPs. This system utilizes a tangential view with a pinhole imaging system and spectral filtering with beryllium foils. SXR emission is chosen to avoid line radiation and allows suitable signal at the top of a H-mode pedestal where T(e)∼1-2 keV. A synthetic diagnostic calculation based on 3D SXR emissivity estimates is used to help assess signal levels and resolution of the design. A signal-to-noise ratio of 10 at 1 cm resolution is expected for the perturbed signals, which are sufficient to resolve most of the predicted vacuum island sizes.

Simulation of a tangential soft x-ray imaging system

Tangentially viewing soft x-ray (SXR) cameras are capable of detecting nonaxisymmetric plasma structures in magnetically confined plasmas. They are particularly useful for studying stationary perturbations or phenomenon that occur on a timescale faster than the plasma rotation period. Tangential SXR camera diagnostics are planned for the DIII-D and NSTX tokamaks to elucidate the static edge magnetic structure during the application of 3D perturbations. To support the design of the proposed diagnostics, a synthetic diagnostic model was developed using the CHIANTI database to estimate the SXR emission. The model is shown to be in good agreement with the measurements from an existing tangential SXR camera diagnostic on NSTX.

Tangential soft-x ray imaging for three-dimensional structural studies in a reversed field pinch

Tangential soft-x ray (SXR) imaging diagnostic has been developed and three-dimensional (3D) structure of the internal magnetic surface has been deduced by comparing the experimental and calculated two-dimensional SXR images in a reversed field pinch. The SXR imaging system, consisting of a MCP, a fluorescent plate, and an intensified charge coupled device camera, has been installed in REversed field pinch of Low-Aspect-ratio eXperiment (RELAX) machine. Major characteristics of an experimental SXR image could be reproduced by numerical calculations of the image using a single island model, suggesting a helical hot core in RELAX. The SXR imaging system could be useful for 3D structural studies when tangential and vertical simultaneous imaging systems would be installed, with appropriate numerical modeling of 3D structure of the magnetic surfaces.

Broad-Band Temporal and Spectral Variation of 36 Active Galactic Nuclei Observed with Suzaku

Abstract 36 AGN data observed by Suzaku were compiled to examine the temporal variability in different energy bands covered by soft X-ray imaging systems (XRT $+$ XIS: 0.5–10 keV) and Hard X-ray Detector (HXD: 15–50 keV) aboard Suzaku. Three band light curves were obtained in L (0.5–2 keV), M (2–10 keV), and H (15–50 keV) with a time binning of 5760 s. The L-band flux change was almost proportional to that of the M-band without offsets in most of type-1 AGNs. The slope ($=$$dL/dM$) of the correlation changed by more than a factor of 10 from Seyfert 2 to narrow-line Seyfert 1 galaxies (NLS1). The power-law component can explain the slope of Seyfert 1 galaxies with a typical index, $\Gamma$, of 1.9. For NLS1 s with steeper slopes, an additional soft excess component is needed, whose variation should be proportional to that of the power-law component. It gives a new constraint to models for the soft excess component. The H-band flux change is a linear function of the M-band flux with a significant offset in the H-band. The slope can be explained by the power-law component with an absorption column from 10$^{22{-}24} $cm$^{-2}$. The offset can be attributed to the reflection component, which is stable on a time scale of days.

Soft X-ray Tomography on HT-7

The soft X-ray imaging system on HT-7 is introduced. Fourier–Bessel expansion method is used to reconstruct the soft X-ray emission distribution. Simulation results show that the inversion accuracy is associated with the angular expansion limit and the hot core displacement. In addition, tomographic results of sawtooth oscillations in a typical low hybrid current drive (LHCD) plasma are presented. It is shown that the reconstructions are reliable to analyze the perturbative mode and the evolution.