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In this paper, we report the absolute measurement of the spectral sensitivity of a bilamellar tube x-ray streak camera (XRSC) over the 0.1–10 keV range equipped with a CsI photocathode for Laser MégaJoule (LMJ) fusion experiments. This calibration of the XRSC is performed in static mode by using two multi-anode x-ray generators. Two silicon drift detectors (SDDs) previously calibrated at the Physikalisch–Technische–Bundesanstalt radiometric laboratory are used as secondary standards. Both x-ray generators work with a specific monochromator for radiometric measurements. In the sub-keV region, a 1 m-grazing incidence Rowland geometry monochromator specifically developed to handle LMJ's x-ray camera is used, whereas for higher energies (>2 keV), a double-crystal monochromator is employed. The absolute spectral sensitivity of the XRSC is obtained by comparing the CCD counts of the XRSC output with the output counts in x-ray lines recorded by the SDD. The results obtained below 1.2 keV are, to our knowledge, the first measurements of the spectral sensitivity of an XRSC in the soft x-ray range with a CsI photocathode. Comparison with a model describing the spectral dependence of the sensitivity of the XRSC revealed that measurements obtained in the sub-keV region are greater than expected, whereas they agree with the model above 4.5 keV. There may be several contributors to this behavior, including the grain morphology of the CsI layer and exposure to air. [ABSTRACT FROM AUTHOR]

We report on the design and implementation of a new system used to characterize the energy-dependent x-ray transmission curve, Θ(E), through filters used in high-energy density physics diagnostics. Using an Amptek X-123-CdTe x-ray spectrometer together with a partially depleted silicon surface barrier detector, both the energy spectrum and total emission of an x-ray source have been accurately measured. By coupling these detectors with a custom PROTO-XRD x-ray source with interchangeable cathodes, accurate characterizations of Θ(E) for filters of varying materials and thicknesses have been obtained. The validity of the technique has been confirmed by accurately reproducing areal densities for high-purity filters with known x-ray transmission properties. In this paper, the experimental setup is described and the results of absorption calibrations performed on a variety of different filters are presented. [ABSTRACT FROM AUTHOR]

The work describes a novel approach to the design of a fast, multichannel measurement system for plasma diagnostics [A. Wojenski et al., Fusion Eng. Des. 123, 727 (2016)]. Its main scope is to provide measurements of soft X-ray (SXR) emission during plasma phenomena at the W-Environment in Steady-state Tokamak (WEST), especially for monitoring and tracing tungsten impurities. This paper describes the vertical Gas Electron Multiplier (GEM) camera installed at the WEST [M. Chernyshova et al., J. Instrument. 10, P10022 (2015)]. The designed GEM detector readout board has more than 100 channels, resulting in high-performance requirements for the data acquisition and processing system. The novel system construction approach is that the unit works on the raw signals providing a high quality of the data, especially in the scope of pileup effect analysis. In the case of doubtful results, the source data can be easily reviewed offline. The data selection and transmission are done in Field-Programmable Gate Arrays (FPGAs) on the custom boards with the custom Peripheral Component Interconnect (PCI)-Express Gen2 switch that allows us to register signals from multiple FPGAs and then process the data by complex algorithms [G. Kasprowicz et al., J. Fusion Energy 38, 480 (2019)]. The firmware is replaceable and different working modes can be applied (some under verification): global trigger mode, high-speed data serialization, and extended signal registration. Low level optimized central processing unit software for data readout was also designed [P. Linczuk et al., J. Instrum. 14, C05001 (2019)]. The installation of the system is described due to complex system components' distribution. The first results of the successful acquisition of the plasma at the WEST are discussed. The corresponding SXR energy and topology spectra were computed. Those are the first technical measurements of the system to ensure verification of data quality. [ABSTRACT FROM AUTHOR]

Soft x-ray (SXR) tomography is a key diagnostic method for impurity transport study in tokamaks since it allows for local impurity density reconstruction. The International Thermonuclear Experimental Reactor (ITER) radiative environment in deuterium–deuterium and deuterium–tritium phases will limit the choices of SXR detector technologies, and gas detectors are one of the most promising solutions. In this paper, we, thus, investigate the SXR tomography possibilities on ITER using Low Voltage Ionization Chambers (LVICs). The study contains the development of a LVIC synthetic diagnostic and its application to estimate the LVIC tomographic capabilities in an ITER D–T scenario, including the influence of LVIC parameters and noise in the measurements. [ABSTRACT FROM AUTHOR]

A novel GEM (Gas Electron Multiplier) system has been installed on experimental advanced superconducting tokamak (EAST) which is used for collecting the line integral of the soft X-ray radiation (SXR) through a pinhole-collimated Beryllium window. The sightline of the 2-D GEM system is tangential to the toroidal field. To obtain the local SXR emission, the Tikhonov algorithm is applied for the imaging of the poloidal cross section emission in the vacuum vessel. In the meanwhile, the L-curve method is used to find an optimized solution of the regularization parameters. The tomography reliability has been tested with a known emission function where the error is also discussed. The tomography method has been coded as a graphic user interface for the fast analysis of GEM experimental data. The typical tomography results have been shown for the EAST shot (#79282) in this paper. [ABSTRACT FROM AUTHOR]

Gaussian process tomography (GPT) is a recently developed tomography method based on the Bayesian probability theory [J. Svensson, JET Internal Report EFDA-JET-PR(11)24, 2011 and Li et al., Rev. Sci. Instrum. 84, 083506 (2013)]. By modeling the soft X-ray (SXR) emissivity field in a poloidal cross section as a Gaussian process, the Bayesian SXR tomography can be carried out in a robust and extremely fast way. Owing to the short execution time of the algorithm, GPT is an important candidate for providing real-time reconstructions with a view to impurity transport and fast magnetohydrodynamic control. In addition, the Bayesian formalism allows quantifying uncertainty on the inferred parameters. In this paper, the GPT technique is validated using a synthetic data set expected from the WEST tokamak, and the results are shown of its application to the reconstruction of SXR emissivity profiles measured on Tore Supra. The method is compared with the standard algorithm based on minimization of the Fisher information. [ABSTRACT FROM AUTHOR]

This paper introduces a novel active snubber cell for soft switching pulse width modulation DC-DC converters. In the proposed converter, the main switch is turned on under zero voltage transition and turned off under zero voltage switching (ZVS). The auxiliary switch is turned on under zero current switching (ZCS) and turned off under zero current transition. The main diode is turned on under ZVS and turned off under ZCS. All of the other semiconductors in the converter are turned on and off with soft switching. There is no extra voltage stress on the semiconductor devices. Besides, the proposed converter has simple structure and ease of control due to common ground. The detailed theoretical analysis of the proposed converter is presented and also verified with both simulation and experimental study at 100 kHz switching frequency and 600 W output power. Furthermore, the efficiency of the proposed converter is 95.7% at nominal power. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a new method to calibrate the absolute sensitivity of a soft X-ray streak camera (SXRSC). The calibrations are done in the static mode by using a small laser-produced X-ray source. A calibrated X-ray CCD is used as a secondary standard detector to monitor the X-ray source intensity. In addition, two sets of holographic flat-field grating spectrometers are chosen as the spectral discrimination systems of the SXRSC and the X-ray CCD. The absolute sensitivity of the SXRSC is obtained by comparing the signal counts of the SXRSC to the output counts of the X-ray CCD. Results show that the calibrated spectrum covers the range from 200 eV to 1040 eV. The change of the absolute sensitivity in the vicinity of the K-edge of the carbon can also be clearly seen. The experimental values agree with the calculated values to within 29% error. Compared with previous calibration methods, the proposed method has several advantages: a wide spectral range, high accuracy, and simple data processing. Our calibration results can be used to make quantitative X-ray flux measurements in laser fusion research. [ABSTRACT FROM AUTHOR]

The soft X-ray (SXR) emission provides valuable insight into processes happening inside of hightemperature plasmas. A standard method for deriving the local emissivity profiles of the plasma from the line-of-sight integrals measured by pinhole cameras is the tomographic inversion. Such an inversion is challenging due to its ill-conditioned nature and because the reconstructed profiles depend not only on the quality of the measurements but also on the inversion algorithm used. This paper provides a detailed description of several tomography algorithms, which solve the inversion problem of Tikhonov regularization with linear computational complexity in the number of basis functions. The feasibility of combining these methods with the minimum Fisher information regularization is demonstrated, and various statistical methods for the optimal choice of the regularization parameter are investigated with emphasis on their reliability and robustness. Finally, the accuracy and the capability of the methods are demonstrated by reconstructions of experimental SXR profiles, featuring poloidal asymmetric impurity distributions as measured at the ASDEX Upgrade tokamak. [ABSTRACT FROM AUTHOR]

Various types of targetry are used nowadays in laser matter interaction experiments. Such targets are characterized using different methods capable of acquiring information about the targets such as density, spatial distribution, and temporal behavior. In this mini-review paper, a particular type of target will be presented. The targets under consideration are gas puff targets of various and novel geometries. Those targets were investigated using extreme ultraviolet (EUV) and soft X-ray (SXR) imaging techniques, such as shadowgraphy, tomography, and pinhole camera imaging. Details about characterization of those targets in the EUV and SXR spectral regions will be presented. [ABSTRACT FROM AUTHOR]

X-ray films remain a key asset for high-resolution x-ray spectral imaging in high-energy-density experiments conducted at the National Ignition Facility (NIF). The soft x-ray Opacity Spectrometer (OpSpec) fielded at the NIF has an elliptically shaped crystal design that measures x rays in the 900–2100 eV range and currently uses an image plate as the detecting medium. However, Agfa D4 and D3sc x-ray films' higher spatial resolution provides increased spectral resolution to the data over the IP-TR image plates, driving the desire for regular use of x-ray film as a detecting medium. The calibration of Agfa D4 x-ray film for use in the OpSpec is communicated here. These calibration efforts are vital to the accuracy of the NIF opacity measurements and are conducted in a previously un-studied x-ray energy range under a new film development protocol required by NIF. The absolute response of Agfa D4 x-ray film from 705 to 4620 eV has been measured using the Nevada National Security Site Manson x-ray source. A broader range of energies was selected to compare results with previously published data. The measurements were taken using selected anodes, filters, and applied voltages to produce well-defined energy lines. [ABSTRACT FROM AUTHOR]

We have developed a new scintillator-based optical soft x-ray (OSXR) diagnostic system for KSTAR. By utilizing fiber optic faceplates, mm-size lens arrays, and fiber bundles, we have successfully constructed a novel optical system for scintillator-based soft x-ray detection to overcome the limited vacuum-port conditions in KSTAR. P47 (Y2SiO5), which has a fast rise (∼7 ns) and decay (∼100 ns) time sufficient for detecting plasma instabilities observed in the kHz–MHz spectral range, was selected as the scintillator material for the KSTAR OSXR system. Scintillation toward each detection channel is collected by the lens arrays coupled to optical fiber cores, which are connected to the photodetector system. Initial results obtained during the 2022 KSTAR experimental campaign support the validity of the OSXR data through the consistency of OSXR measurement results with other diagnostics. We also observe that the OSXR system can capture magnetohydrodynamic activities, such as sawtooth oscillations, and provide valuable information for disruption mitigation studies using shattered pellet injection. [ABSTRACT FROM AUTHOR]

Soft x-ray diffraction gratings coated with a supermirror-type multilayer were designed to enhance diffraction efficiency in the energy range of 2–4 keV by means of numerical calculations. The optimized groove depth and incidence angle are 2.05 nm and 88.65°, respectively, for the grating having a groove density of 3200 grooves/mm. Regarding the multilayer structure, the optimum number of B4C/W layers pair was 11 and the thickness of B4C was increased from bottom to top, while that of W was kept constant. The replacement of the top layer of W by either Co, Cr, or Ni was an effective means of obtaining uniform diffraction efficiency. In the region of 2–4 keV, the calculated diffraction efficiency of the designed gratings was up to ∼5.3%, on average, and almost eight times larger than that of ∼0.7% of an Au coated grating. [ABSTRACT FROM AUTHOR]

In this Review Article, we discuss a range of soft x-ray power diagnostics at inertial confinement fusion (ICF) and pulsed-power fusion facilities. This Review Article describes current hardware and analysis approaches and covers the following methods: x-ray diode arrays, bolometers, transmission grating spectrometers, and associated crystal spectrometers. These systems are fundamental for the diagnosis of ICF experiments, providing a wide range of critical parameters for the evaluation of fusion performance. [ABSTRACT FROM AUTHOR]

Smaller and more complex nanostructures in the semiconductor industry require a constant upgrade of accompanying metrological methods and equipment. A central task for nanometrology is the precise determination of structural features of gratings in the nanometer range as well as their elemental composition. Scatterometry and x-ray fluorescence in the soft x-ray and extreme ultraviolet spectral ranges are ideally suited to this task. We here present a new, compact measurement chamber that can simultaneously detect the elastically scattered signal and the fluorescence, originating from nanoscale grating samples. Its geometry enables detecting scattered intensity over a wide angular range with a variable angle of incidence. We show first experiments on industry-relevant test structures from the commissioning process alongside the specifications of the setup, located at PTB's soft x-ray radiometry beamline at the synchrotron radiation facility BESSY II in Berlin. [ABSTRACT FROM AUTHOR]

Bimorph mirrors place stringent requirements on the welding technology of silicon substrates and piezoelectric ceramics to ensure their ultrahigh-vacuum compatibility. Conventional welding techniques usually require high temperature and pressure, which have a high impact on the welding substrate, while the use of organic adhesives for bonding does not guarantee their stability in ultrahigh vacuum. Here, the transient liquid phase bonding technology based on an Au–In metal system was studied to meet the requirement for ultrahigh-vacuum application. The microstructure, chemical composition, and related mechanical properties of the bonding at different welding conditions were investigated. Meanwhile, the piezo ceramics and the bond were baked at 150 °C to test the stability. The results show that a stable bonding was achieved between centimeter-scaled single crystal silicon and lead zirconate titanate ceramics at 200 °C temperature and 2.5 MPa pressure, and the piezo ceramics and the bond are not damaged by baking to 150 °C for 48 h. [ABSTRACT FROM AUTHOR]

Talbot–Lau x-ray interferometry is a refraction-based diagnostic that can map electron density gradients through phase-contrast methods. The Talbot–Lau x-ray deflectometry (TXD) diagnostics have been deployed in several high energy density experiments. To improve diagnostic performance, a monochromatic TXD was implemented on the Multi-Tera Watt (MTW) laser using 8 keV multilayer mirrors (Δθ/θ = 4.5%-5.6%). Copper foil and wire targets were irradiated at 1014–1015 W/cm2. Laser pulse length (∼10 to 80 ps) and backlighter target configurations were explored in the context of Moiré fringe contrast and spatial resolution. Foil and wire targets delivered increased contrast <30%. The best spatial resolution (<6 μm) was measured for foils irradiated 80° from the surface. Further TXD diagnostic capability enhancement was achieved through the development of advanced data postprocessing tools. The Talbot Interferometry Analysis (TIA) code enabled x-ray refraction measurements from the MTW monochromatic TXD. Additionally, phase, attenuation, and dark-field maps of an ablating x-pinch load were retrieved through TXD. The images show a dense wire core of ∼60 μm diameter surrounded by low-density material of ∼40 μm thickness with an outer diameter ratio of ∼2.3. Attenuation at 8 keV was measured at ∼20% for the dense core and ∼10% for the low-density material. Instrumental and experimental limitations for monochromatic TXD diagnostics are presented. Enhanced postprocessing capabilities enabled by TIA are demonstrated in the context of high-intensity laser and pulsed power experimental data analysis. Significant advances in TXD diagnostic capabilities are presented. These results inform future diagnostic technique upgrades that will improve the accuracy of plasma characterization through TXD. [ABSTRACT FROM AUTHOR]

Measurements of radiated power are critical for characterizing and optimizing tokamak performance. The RADCAM system, comprising arrays of foil bolometers, Absolute eXtreme UltraViolet (AXUV), and filtered soft x-ray diodes, has been constructed to provide improved measurements of plasma radiation on "Tokamak a Configuration Variable" (TCV). An overview of the physical geometry, electronics, and design of the system is provided. The construction of the bolometer foils together with the improved sensitivity characteristics resulting from the inclusion of an anti-reflection carbon coating are presented. The large number of lines of sight in RADCAM are shown to significantly increase the spatial resolution over the legacy system. The system calibration procedure is detailed, and the mean system sensitivity is shown to vary by less than 5% over 1000 discharges. Additionally, the methodology for cross-calibration of the AXUV diodes with the bolometer foils is presented and applied to generate high temporal resolution measurements. The RADCAM radiation camera system is a compact, versatile system that is demonstrated to provide high resolution profiles of the radiated power in TCV. [ABSTRACT FROM AUTHOR]

The C-2W experimental device at TAE Technologies utilizes neutral beam injection and edge biasing to sustain long-lived, stable field reversed configuration (FRC) plasma. An ongoing effort is under way to optimize the electrode biasing system, which provides boundary control to stabilize the FRC. To this end, tomography offers a powerful and non-invasive technique as tomographic reconstruction of the FRC emission profile provides an important assessment of global stability. Recently, a new signal acquisition system was implemented on a bolometer array dedicated to tomography on C-2W, significantly enhancing the signal-to-noise of the collected data. The array consists of 300 simultaneously digitized photodiode channels that respond to a broad range of wavelengths, from soft x-ray to near-infrared, as well as energetic particles, yielding 180 unique lines of sight that intersect a toroidal plane of the FRC near the mid-plane. Utilizing the collected photo-signals from a set of plasma discharges in which the electrode biasing was intentionally terminated mid-shot, time-resolved reconstruction of the plasma emissivity is achieved via pixel-based 1D and 2D tomographic algorithms, revealing sharply annular profiles with a clear magnetohydrodynamic (MHD) mode structure. In addition, reconstruction of the plasma center-of-emission trajectories via a centroid algorithm applied to the same set of discharges demonstrates a cyclical plasma wobble. Crucially, both the tomography reconstruction and centroid reconstruction indicate an n = 1 toroidal mode that reverses from the electron diamagnetic direction to the ion diamagnetic direction and grows in amplitude after bias termination, qualitatively consistent with the expected stabilizing effect of electrodes. [ABSTRACT FROM AUTHOR]

When compared with the National Ignition Facility's (NIF) original soft x-ray opacity spectrometer, which used a convex cylindrical design, an elliptically shaped design has helped to increase the signal-to-noise ratio and eliminated nearly all reflections from alternate crystal planes. The success of the elliptical geometry in the opacity experiments has driven a new elliptical geometry crystal with a spectral range covering 520–1100 eV. When coupled with the primary elliptical geometry, which spans 1000–2100 eV, the new sub-keV elliptical geometry helps to cover the full iron L-shell and major oxygen transitions important to solar opacity experimentation. The new design has been built and tested by using a Henke x-ray source and shows the desired spectral coverage. Additional plans are underway to expand these opacity measurements into a mode of time-resolved detection, ∼1 ns gated, but considerations for the detector size and photometrics mean a crystal geometry redesign. The new low-energy geometry, including preliminary results from the NIF opacity experiments, is presented along with the expansion plans into a time-resolved platform. [ABSTRACT FROM AUTHOR]

We describe a method to reduce vacuum ultraviolet (VUV) pulse pileup (PPU) in x-ray pulse-height Silicon Drift Detector (SDD) signals. An Amptek FAST SDD, with C1 (Si3N4) window, measures bremsstrahlung emitted from PFRC-2 plasma to extract the electron temperature (Te) and density (ne). The C1 window has low transmissivity for photons with energy below 200 eV though will transmit some VUV and soft x-ray photons, which PFRC-2 plasmas abundantly emit. Multi-VUV-photon PPU contaminates the interpretation of x rays with energy > 100 eV, particularly in a low-energy exponential tail. The predicted low transmissivity of ∼1 μm thick Mylar [polyethylene terephthalate (PET)] to photons of energy < 100 eV led to the selection of Mylar as the candidate filter to reduce VUV PPU. Experiments were conducted on an x-ray tube with a graphite target and on a quasi-Maxwellian tenuous plasma (ne ∼ 109 cm−3) with effective temperatures reaching 1500 eV. A Mylar filter thickness of 850 nm is consistent with the results. The Mylar-filter-equipped SDD was then used on the PFRC-2 plasma, showing a substantial reduction in the low-energy x-ray signal, supporting our hypothesis of the importance of VUV PPU. We describe the modeling and experiments performed to characterize the effect of the Mylar filter on SDD measurements. [ABSTRACT FROM AUTHOR]

A new soft x-ray (SXR) array diagnostic system has been developed on versatile experiment spherical torus (VEST) for measurements of 2D SXR emissivity profile and identification of poloidal mode structure. Through tomographic inversion techniques, 2D SXR emissivity profile can be acquired from the line-integrated SXR data, which enables the visualization of mode structure of plasma instability, such as the magnetohydrodynamics mode. The SXR array diagnostic system consists of two 20-channel arrays positioned at the middle and the top on the same poloidal plane for horizontal and vertical lines of sight, respectively. Each array of the diagnostic system uses absolute extreme ultraviolet photodiode array as the detector. To apply appropriate filters (up to four) for different energy regimes without breaking the vacuum, a filter wheel and its rotatable vacuum feed-through are installed behind the pinhole. SXR data are acquired with a digitizer at the sampling rate of up to 125 MHz. Finally, we discuss initial measurement data obtained from Ohmic plasma in VEST. [ABSTRACT FROM AUTHOR]

A high spatial and temporal resolution soft x-ray (SXR) imaging diagnostic has been installed in EAST for the study of magnetohydrodynamics activities and core high-Z impurity transport. Up to 122 lines of sight view the poloidal plasma from three directions (two up-down symmetrical horizontal arrays and one vertical array), which renders the diagnostic able to provide detailed tomographic reconstructions under various conditions. Fourier-Bessel method based on flux coordinates was employed for 2-D SXR tomographic reconstruction. Examples of several events measured by SXR diagnostic in EAST are shown, namely the crash patterns of sawtooth, periodical burst of edge localized modes, and the transport of high-Z intrinsic impurities. [ABSTRACT FROM AUTHOR]

We demonstrate the use of three diagnostic tools which simultaneously view the target from nearly the same direction, and their results are combined to provide temporally, spectrally, and spatially resolved absolutely calibrated target emission information. To demonstrate this capability, Au targets were irradiated by 1.8 kJ, 3 ns laser pulses to produce broadband soft x-ray emission in the 0.1–3.5 keV spectral range. Target diagnostics included a time-resolved x-ray diode array, each measured a partial spectral band, time-integrated spectrally resolved absolutely calibrated transmission grating spectrometer, and static and time-resolved soft x-ray imagers coupled to a charge-coupled device camera and to a streak camera, respectively, measuring spatially and temporally resolved radiation at the main Au target emission bands. The combined temporally, spectrally, and spatially resolved absolutely calibrated target emission result can be compared to simulations and be used to design and analyze experiments in which the source emission is used as a drive for various physical processes. [ABSTRACT FROM AUTHOR]

The Soft X-Ray (SXR) tomography system on the Madison Symmetric Torus uses four cameras to determine the emissivity structure of the plasma. This structure should directly correspond to the structure of the magnetic field; however, there is an apparent phase difference between the emissivity reconstructions and magnetic field reconstructions when using a cylindrical approximation. The difference between the phase of the dominant rotating helical mode of the magnetic field and the motion of the brightest line of sight for each SXR camera is dependent on both the camera viewing angle and the plasma conditions. Holding these parameters fixed, this phase difference is shown to be consistent over multiple measurements when only toroidal or poloidal magnetic field components are considered. These differences emerge from physical effects of the toroidal geometry which are not captured in the cylindrical approximation. [ABSTRACT FROM AUTHOR]

Soft x-ray detection with the new "multi-energy" PILATUS3 detector systems holds promise as a magnetically confined fusion (MCF) plasma diagnostic for ITER and beyond. The measured x-ray brightness can be used to determine impurity concentrations, electron temperatures, n2eZeff products, and to probe the electron energy distribution. However, in order to be effective, these detectors which are really large arrays of detectors with photon energy gating capabilities must be precisely calibrated for each pixel. The energy-dependence of the detector response of the multi-energy PILATUS3 system with 100 K pixels has been measured at Dectris Laboratory. X-rays emitted from a tube under high voltage bombard various elements such that they emit x-ray lines from Zr-Lα to Ag-Kα between 1.8 and 22.16 keV. Each pixel on the PILATUS3 can be set to a minimum energy threshold in the range from 1.6 to 25 keV. This feature allows a single detector to be sensitive to a variety of x-ray energies, so that it is possible to sample the energy distribution of the x-ray continuum and line-emission. PILATUS3 can be configured for 1D or 2D imaging of MCF plasmas with typical spatial energy and temporal resolution of 1 cm, 0.6 keV, and 5 ms, respectively. [ABSTRACT FROM AUTHOR]

Soft x-ray emission from laser irradiated gold foils was measured at the Omega-60 laser system using the Dante photodiode array. The foils were heated with 2 kJ, 6 ns laser pulses and foil thicknesses were varied between 0.5, 1.0, and 2.0 μm. Initial Dante analysis indicates peak emission temperatures of roughly 100 eV and 80 eV for the 0.5 μm and 1.0 μm thick foils, respectively, with little measurable emission from the 2.0 μm foils. [ABSTRACT FROM AUTHOR]

An innovative tangential-view soft x-ray (SXR) tomographic imaging measurement was developed on the TS-6 spherical tokamak merging device as a key diagnostic for investigating the mechanism of electron acceleration. In order to measure SXR with different energy ranges, two micro-channel plates (MCPs) are, respectively, installed in two vacuum chambers, which are equipped with different filters. Especially designed lenses and fiber bundles serve as an optical system to transfer images from phosphor plates of MCPs to a high speed imaging system. This design also enables us to simultaneously measure two images appearing on phosphor plates of MCPs by just one high speed imaging system. The temporal and spatial resolution of this diagnostic can be up to 5 µs and 4 mm, respectively, at present. The tomographic method based on the Phillips–Tikhonov regularization is employed to reconstruct line-integrated images into the local emissivity of SXR, which reflects the spatial distribution of high-energy electrons. Owing to this diagnostic, we successfully measured SXR emitted from the downstream region of magnetic reconnection in TS-6 merging experiments for the first time. The energy range of SXR turned out to be higher than 100 eV but lower than 400 eV. [ABSTRACT FROM AUTHOR]

A multi-energy soft x-ray pinhole camera has been designed, built, and deployed at the Madison Symmetric Torus to aid the study of particle and thermal transport, as well as MHD stability physics. This novel imaging diagnostic technique employs a pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently on each pixel. The detector of choice is a PILATUS3 100 K with a 450 μm thick silicon sensor and nearly 100 000 pixels sensitive to photon energies between 1.6 and 30 keV. An ensemble of cubic spline smoothing functions has been applied to the line-integrated data for each time-frame and energy-range, obtaining a reduced standard-deviation when compared to that dominated by photon-noise. The multi-energy local emissivity profiles are obtained from a 1D matrix-based Abel-inversion procedure. Central values of Te can be obtained by modeling the slope of the continuum radiation from ratios of the inverted radial emissivity profiles over multiple energy ranges with no a priori assumptions of plasma profiles, magnetic field reconstruction constraints, high-density limitations, or need of shot-to-shot reproducibility. In tokamak plasmas, a novel application has recently been tested for early detection, 1D imaging, and study of the birth, exponential growth, and saturation of runaway electrons at energies comparable to 100 × Te,0; thus, early results are also presented. [ABSTRACT FROM AUTHOR]

In our recent study [Fu et al., Commun. Phys. 3(1), 92 (2020)], we have developed an approach for energy-scaling of high-order harmonic generation in the water-window region under a neutral-medium condition. More specifically, we obtained a nanojoule-class water-window soft x-ray harmonic beam under a phase-matching condition. It has been achieved by combining a newly developed terawatt-class mid-infrared femtosecond laser and a loose-focusing geometry for high-order harmonic generation. The generated beam is more than 100 times intense compared to previously reported results. The experimental setup included two key parts: a terawatt mid-infrared femtosecond driving laser [Fu et al., Sci. Rep. 8(1), 7692 (2018)] and a specially designed gas cell. Despite the dramatic drop in the optimal gas pressure for phase-matching due to loose-focusing geometry, it still reached the 1 bar level for helium. Thus, we have designed a double-structured pulsed-gas cell with a differential pumping system, which enabled providing sufficiently high gas pressure. Moreover, it allowed reducing gas consumption significantly. A robust energy-scalable apparatus for high-order harmonic generation developed in this study will enable the generation of over ten-nanojoule water-window attosecond pulses in the near future. [ABSTRACT FROM AUTHOR]

A new pseudolocal tomography algorithm is developed for soft X-ray(SXR) imaging measurements of the turbulent electron temperature fluctuations (δ Te) in tokamaks and stellarators. The algorithm overcomes the constraints of limited viewing ports on the vessel wall (viewing angle) and limited number of lines of sight (LOS). This is accomplished by increasing the number of LOS locally in a region of interest. Numerical modeling demonstrates that the wavenumber spectrum of the turbulence can be reliably reconstructed, with an acceptable number of viewing angles and LOS and suitable low SNR detectors. We conclude that a SXR imaging diagnostic for measurements of turbulent δ Te using a pseudolocal reconstruction algorithm is feasible. [ABSTRACT FROM AUTHOR]

We develop a filtered absolute extreme ultraviolet (AXUV) diode array to measure the time evolution of the soft x-ray spectrum in the energy range of 1–10 keV. AXUV–HS5, the detector, has a fast rise time of 0.7 ns, a wide energy detection range, and high accessibility. We use Geant4 simulations to design an appropriate filter set for flat-and-sharp virtual channels (VCs), where a filter with no spectral edge removes large tails of the response curves. A Levenberg–Marquardt (LM) method, sensitive to the expected spectral function, is improved to reliably generate a continuous radiation spectrum, by utilizing spectral information from the least-squares (LS) method that reconstructs a discrete spectrum with low spectral resolution directly from the VCs. We test the filtered AXUV diode array on an X-pinch device with a peak current of 140 kA at Seoul National University; the array with ten channels is installed in a vacuum chamber. For a two-wire 40 μm stainless steel X-pinch, x-ray power, radiation temperature, and the reconstructed x-ray spectrum are obtained from the filtered AXUV diode array by the combined LS–LM method. [ABSTRACT FROM AUTHOR]

A toroidal soft x-ray array system for spectrum and intensity measurements on the EXL-50 spherical tokamak is described. Silicon drift detectors and digital multichannel analyzers are adopted for all 21 channels of the array, and an average energy resolution of 147 eV at 5.89 keV has been achieved at count rates over 500 kcps. In total, 20 channels of the array are symmetrically observed in both co- and counter-current directions on the EXL-50 mid-plane with a spatial resolution of around 10 cm, and the remaining one serves as a background reference channel. Tungsten emissions from tungsten coating of the limiters on the central post are observed. The influence of hard x rays on measured soft x-ray spectra and system operation is discussed. [ABSTRACT FROM AUTHOR]

A bolometer/soft x-ray diagnostic based on modular absolute extreme ultraviolet photodiodes has been built to obtain the local emission profile of a poloidal cross section in Sino-UNIted Spherical Tokamak (SUNIST). The system consists of seven photodiode arrays of 112 channels located around the low field side of a poloidal cross section. All arrays are mounted into 81 × 36 × 33 mm3 modules, which could be installed flexibly on the wall of the vacuum vessel. Tungsten shields with adjustable pinholes restrict the radiation flux. Compact flexible printed circuits with multilayer copper polygon poured on both sides are designed to transmit signals with electronic noise, which is reduced to less than 1/10 before. A two-stage transimpedance amplifier array of 700 kHz bandwidth is fixed on the atmosphere side of a vacuum electrical feedthrough and is powered by battery packs. A synchronized switch shuts down the circuit to reduce the heat production and increase the battery life. A line-integrated radiation emission profile with 2 cm spatial resolution and temporal resolution up to 2 µs is obtained, and the local emission profile of SUNIST is reconstructed with the help of a newly developed tomography scheme for movable detector modules. [ABSTRACT FROM AUTHOR]

A compact multi-energy soft x-ray diagnostic is being installed on the W Environment in Steady-state Tokamak (WEST), which was designed and built to test ITER-like tungsten plasma facing components in a long pulse (∼1000 s) scenario. The diagnostic consists of a pinhole camera fielded with the PILATUS3 photon-counting Si-based detector (≲100 kpixel). The detector has sensitivity in the range 1.6–30 keV and enables energy discrimination, providing a higher energy resolution than conventional systems with metal foils and diodes with adequate space and time resolution (≲1 cm and 2 ms). The lower-absorption cut-off energy is set independently on each one of the ∼100 kpixels, providing a unique opportunity to measure simultaneously the plasma emissivity in multiple energy ranges and deduce a variety of plasma parameters (e.g., Te, nZ, and ΔZeff). The energy dependence of each pixel is calibrated here over the range 3–22 keV. The detector is exposed to a variety of monochromatic sources—fluorescence emission from metallic targets—and for each pixel, the lower energy threshold is scanned to calibrate the energy dependence. The data are fit to a responsivity curve ("S-curve") that determines the mapping between the possible detector settings and the energy response for each pixel. Here, the calibration is performed for three energy ranges: low (2.3–6 keV), medium (4.5–13.5 keV), and high (5.4–21 keV). We determine the achievable energy resolutions for the low, medium, and high energy ranges as 330 eV, 640 eV, and 950 eV, respectively. The main limitation for the energy resolution is found to be the finite width of the S-curve. [ABSTRACT FROM AUTHOR]

The soft x-ray Opacity Spectrometer (OpSpec) used on the National Ignition Facility (NIF) has recently incorporated an elliptically shaped crystal. The original OpSpec used two convex cylindrical crystals for time-integrated measurements of point-projection spectra from 540 to 2100 eV. However, with the convex geometry, the low-energy portion of the spectrum suffered from high backgrounds due to scattered x-rays as well as reflections from alternate crystal planes. An elliptically shaped crystal allows an acceptance aperture at the crossover focus between the crystal and the detector, which reduces background and eliminates nearly all reflections from alternate crystal planes. The current elliptical design is an improvement from the convex cylindrical design but has a usable energy range from 900 to 2100 eV. In addition, OpSpec is currently used on 18 NIF shots/year, in which both crystals are typically damaged beyond reuse, so efficient production of 36 crystals/year is required. Design efforts to improve the existing system focus on mounting reliability, reducing crystal strain to increase survivability between mounting and shot time, and extending the energy range of the instrument down to 520 eV. The elliptical design, results, and future options are presented. [ABSTRACT FROM AUTHOR]

High-temperature, high-density experiments require a simultaneous understanding of temporal and spectral regions. The spectral x-ray streak camera (SXSC) is a new high-temporal-resolution spectral x-ray diagnostic system that allows researchers to differentiate between soft and hard x-ray regions. The diagnostic offers three spectral channels with a wide spectral range, one direct channel that includes a filter and two indirect channels that include both mirrors and filters. The opto-mechanical design positions the filtered radiation at three different locations along the streak photo-cathode (PC) slit to provide time-dependent spectral channels with pico-second temporal resolution. A moderate spatial resolution (150–700 μm) is achieved using slits perpendicular to the PC slit, while the slit width is optimized according to the central channel wavelength (for each channel). The diagnostic system covers a spectral range of 30–500 eV for the mirror channels and >1300 eV for the direct channel. The temporal and spatial axes of the streak camera are calibrated with respect to a sequence of x-ray pulses. The SXSC diagnostic system is tested and analyzed using Marshak-wave emission from an SiO2 foam that was heated by a laser-beam irradiated halfraum. The SXSC results are compared to measurements from an x-ray diode array with similar spectral channels. [ABSTRACT FROM AUTHOR]

A major upgrade has been implemented for the ns-gated laser entrance hole imager on the National Ignition Facility (NIF) to obtain high-quality data for Hohlraum physics study. In this upgrade, the single "Furi" hCMOS sensor (1024 × 448 pixel arrays with two-frame capability) is replaced with dual "Icarus" sensors (1024 × 512 pixel arrays with four-frame capability). Both types of sensors were developed by Sandia National Laboratories for high energy density physics experiments. With the new Icarus sensors, the new diagnostic provides twice the detection area with improved uniformity, wider temporal coverage, flexible timing setup, and greater sensitivity to soft x rays (<2 keV). These features, together with the fact that the diagnostic is radiation hardened and can be operated on the NIF for high neutron yield deuterium–triterium experiments, enable significantly greater return of data per experiment. [ABSTRACT FROM AUTHOR]

Uniform large transition-edge sensor (TES) arrays are fundamental for the next generation of x-ray space observatories. These arrays are required to achieve an energy resolution ΔE < 3 eV full width at half maximum (FWHM) in the soft x-ray energy range. We are currently developing x-ray microcalorimeter arrays for use in the future laboratory and space-based x-ray astrophysics experiments and ground-based spectrometers. In this contribution, we report on the development and the characterization of a uniform 32 × 32 pixel array with 140 × 30 μm2 Ti/Au TESs with the Au x-ray absorber. We report on extensive measurements on 60 pixels in order to show the uniformity of our large TES array. The averaged critical temperature is Tc = 89.5 ± 0.5 mK, and the variation across the array (∼1 cm) is less than 1.5 mK. We found a large region of detector's bias points between 20% and 40% of the normal-state resistance where the energy resolution is constantly lower than 3 eV. In particular, results show a summed x-ray spectral resolution ΔEFWHM = 2.50 ± 0.04 eV at a photon energy of 5.9 keV, measured in a single-pixel mode using a frequency domain multiplexing readout system developed at SRON/VTT at bias frequencies ranging from 1 MHz to 5 MHz. Moreover, we compare the logarithmic resistance sensitivity with respect to temperature and current (α and β, respectively) and their correlation with the detector's noise parameter M, showing a homogeneous behavior for all the measured pixels in the array. [ABSTRACT FROM AUTHOR]

The photoabsorption spectroscopic studies (PASS) beamline (PASS-BL07), installed at a bending magnet 450 MeV, 100 mA Indus-1 synchrotron source (India), is capable of performing photoabsorption studies in the vacuum ultraviolet to soft x-ray range of thin films and solid samples. The beamline covers an energy range of 55 eV–840 eV by an in-house developed SX-700 type plane grating monochromator. This energy range will cover the absorption spectra of low Z-elements like C, N, and O as well as the L and M threshold of 3d elements such as Ti, V, S, etc. The beamline will be significantly used for studying organic semiconductors, graphene, etc. In this article, the design details of the beamline and some of the recent scientific results have been presented. [ABSTRACT FROM AUTHOR]

We present an approach to determine the absolute thickness profile of flat liquid jets, which takes advantage of the information of thin film interference combined with light absorption, both captured in a single microscopic image. The feasibility of the proposed method is demonstrated on our compact experimental setup used to generate micrometer thin, free-flowing liquid jet sheets upon collision of two identical laminar cylindrical jets. Stable operation was achieved over several hours of the flat jet in vacuum (10−4 mbar), making the system ideally suitable for soft x-ray photon spectroscopy of liquid solutions. We characterize the flat jet size and thickness generated with two solvents, water and ethanol, employing different flow rates and nozzles of variable sizes. Our results show that a gradient of thickness ranging from a minimal thickness of 2 µm to over 10 µm can be found within the jet surface area. This enables the tunability of the sample thickness in situ, allowing the optimization of the transmitted photon flux for the chosen photon energy and sample. We demonstrate the feasibility of x-ray absorption spectroscopy experiments in transmission mode by measuring at the oxygen K-edge of ethanol. Our characterization method and the description of the experimental setup and its reported performance are expected to expand the range of applications and facilitate the use of flat liquid jets for spectroscopy experiments. [ABSTRACT FROM AUTHOR]

Gaussian process tomography (GPT) is a method used for obtaining real-time tomographic reconstructions of the plasma emissivity profile in tokamaks, given some model for the underlying physical processes involved. GPT can also be used, thanks to Bayesian formalism, to perform model selection, i.e., comparing different models and choosing the one with maximum evidence. However, the computations involved in this particular step may become slow for data with high dimensionality, especially when comparing the evidence for many different models. Using measurements collected by the Soft X-Ray (SXR) diagnostic in the ASDEX Upgrade tokamak, we train a convolutional neural network to map SXR tomographic projections to the corresponding GPT model whose evidence is highest. We then compare the network's results, and the time required to calculate them, with those obtained through analytical Bayesian formalism. In addition, we use the network's classifications to produce tomographic reconstructions of the plasma emissivity profile. [ABSTRACT FROM AUTHOR]

We report on the functional capabilities of our field emission (FE) measurement systems. The samples are prepared and inserted under clean room conditions and can be precisely xyz-positioned, heat-treated, and investigated in different vacuum environments and temperatures. The FE scanning microscope is a unique microscope being used for the localization of FE sites with high lateral resolution by means of extraction voltage U(x, y) or emission current I(x, y) maps over the cathode area of 25 × 25 mm2 and measuring the FE properties of localized emission sites or individual emitters. In contrast, the integral measurement system with the luminescent screen provides real-time integral information about the distribution of emission sites over the whole cathode during long- and short-term current stability measurements, thus allowing us to investigate the properties of various materials and their applications. Commissioning results with the upgraded systems using a silicon emitter array and a point-type graphene emitter will be given to demonstrate that both FE measurement techniques are very useful for an improved understanding and tailoring of materials for applications. The results showed that point-type graphene emitters are more preferable for practical applications. Using simulation software, a suitable triode configuration for point emitters was designed, and a current transmission ratio of ∼100% was obtained. The FE current stability of graphene emitters at pressures >10−3 Pa can be improved by heating the cathode at 100 °C–300 °C for 1 min–30 min. Finally, point-type graphene film emitters were used for transmission-type x-ray sources, and their applications in imaging and fluorescence spectroscopy are presented. [ABSTRACT FROM AUTHOR]

Resonant elastic x-ray scattering has been widely employed for exploring complex electronic ordering phenomena, such as charge, spin, and orbital order, in particular, in strongly correlated electronic systems. In addition, recent developments in pump–probe x-ray scattering allow us to expand the investigation of the temporal dynamics of such orders. Here, we introduce a new time-resolved Resonant Soft X-ray Scattering (tr-RSXS) endstation developed at the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL). This endstation has an optical laser (wavelength of 800 nm plus harmonics) as the pump source. Based on the commissioning results, the tr-RSXS at PAL-XFEL can deliver a soft x-ray probe (400 eV–1300 eV) with a time resolution of ∼100 fs without jitter correction. As an example, the temporal dynamics of a charge density wave on a high-temperature cuprate superconductor is demonstrated. [ABSTRACT FROM AUTHOR]

Cubic spline interpolation is able to recover temporally and spectrally resolved soft x-ray fluxes from an array of K-edge filtered x-ray diodes without the need for a priori assumptions about the spectrum or the geometry of the emitting volume. The mathematics of the cubic spline interpolation is discussed in detail. The analytic nature of the cubic spline solution allows for analytical error propagation, and the method of calculating the error for radiation temperature, spectral power, and confidence intervals of the unfolded spectrally resolved flux is explained. An unfold of a blackbody model demonstrates the accuracy of the cubic spline unfold. Tests of cubic spline performance using spectrally convolved detailed atomic model simulation results have been performed to measure the method's ability to conserve spectral power to within a factor of 2 or better in line-dominated regimes. The unfold is also demonstrated to work when information from the x-ray diode array is limited due to high signal-to-noise ratios or the lack of signal due to over-attenuation or over-filtration of the x-ray diode signal. The robustness of the unfold with respect to background subtraction and raw signal processing, signal alignment between diode traces, limited signal information, and initial conditions is discussed. Results from an example analysis of a halfraum drive are presented to demonstrate the capabilities of the unfold in comparison with previously established methods. [ABSTRACT FROM AUTHOR]

A high-resolution laboratory reflectometer designed for operation in the soft x-ray (SXR) and extreme ultraviolet (EUV) ranges is described. High spectral resolution, up to 0.028 nm, in a wide spectral range is achieved due to the Czerny–Turner monochromator. A laser plasma generated by irradiating a solid-state target with a focused laser beam (wavelength 1.06 µm, pulse energy 0.5 J, duration 4 ns, and pulse repetition rate 10 Hz) is used as a source of SXR and EUV radiation. The goniometer allows the study of curved optical elements with an aperture up to NA = 0.5 and a diameter of up to 500 mm. The methods providing high efficiency of the optical system and spectral resolution in a wide range of wavelengths are described in detail. The problem of taking into account high orders in the recorded spectra of a laser plasma is discussed. A comparison of the measurement results with the described reflectometer and the optics beamline at the BESSY-II synchrotron is given. [ABSTRACT FROM AUTHOR]

We have designed, built, and tested a climate-controlled, radiation-shielded incubator cabinet for the purpose of analyzing the effects of low-dose x-ray radiation on biological tissues and cell cultures. Bremsstrahlung x rays incident on exchangeable fluorescence plates produce strong, quasi-monochromatic radiation directed toward a small container of biological samples. The x-ray source, sample, and detector are enclosed in an incubator—maintaining the optimal environment for biological samples to increase longevity to a maximum of 72 h. To demonstrate the capabilities of the setup, an example experiment is presented. Rat vascular smooth muscle cell growth was observed after irradiation with characteristic x rays of iron, copper, and calcium to impart doses of 2 mGy each. Cultures show significant spectrum dependent increases in cell number over controls at 48 h after irradiation. The experiment lends credence to the efficacy of the apparatus and shows promise for future low-dose bio-radiation studies. [ABSTRACT FROM AUTHOR]

In the field of pulse-power, there has always been an interest on small and medium size pulsed-current generators (≤2 MA) which are affordable and of low maintenance. We developed the GLIDER, a compact and modular generator, that drives a gas-puff z-pinch load as a soft x-ray source (0.1–1 keV) for laboratory astrophysics absorption experiments. It comprises 48 bricks, tightly packed in a 1.7 m × 3.5 m × 0.8 m transformer oil container. Its compactness and reliability was enabled owing to unique multilayered oil-soaked insulators, and more than 100 post-hole convolutes. Its stripline includes interchangeable tiles for ease of construction and maintenance. Six triggering units enable current pulse shaping. The GLIDER was tested up to ±60 kV (34 kJ) and produced 2 MA in 450 ns rise time on a 5 nH load. We present grating spectra of K-shell absorption of neutral O and N proving the experimental concept and demonstrating column density and ionization measurements. [ABSTRACT FROM AUTHOR]

We present a stability investigation of the Stockholm laboratory cryo soft x-ray microscope. The microscope operates at a wavelength of 2.48 nm and can image biological samples at liquid-nitrogen temperatures in order to mitigate radiation damage. We measured the stability of the two most critical components, sample holder and optics holder, in vacuo and at cryo temperatures at both short and long time scales with a fiber interferometer. Results revealed vibrations in the kHz range, originating mainly from a turbo pump, as well as long term drifts in connection with temperature fluctuations. With improvements in the microscope, earlier stability issues vanished and close-to diffraction-limited imaging could be achieved. Moreover, our investigation shows that fiber interferometers are a powerful tool in order to investigate position-sensitive setups at the nanometer level. [ABSTRACT FROM AUTHOR]