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This paper defines the exact conditions for the application of a previously proposed, general, non-astigmatic, imaging scheme, consisting of a matched pair of spherically bent crystals or reflectors, to x rays. These conditions lead to two specific experimental arrangements, of which one can provide large magnifications. Potential applications include the x-ray diagnosis of laser-produced plasmas and x-ray imaging of, e.g., biological samples, using the highly monochromatic radiation at synchrotron light sources. The results obtained for x rays are, however, valid for a wide spectrum of the electromagnetic radiation so that, for instance, an application of one of the imaging schemes to lithography in the EUV wavelength range should also be possible, if the spherically bent crystals are replaced by appropriate spherical reflectors. Also described is the design of an x-ray crystal spectrometer, which meets the here defined, necessary requirements for the observation of the x-ray spectra of helium-like argon.

A high-resolution x-ray spectrometer was coupled with an ultrafast x-ray streak camera to produce time-resolved line shape spectra measured from hot, solid-density plasmas. A Bragg crystal was placed near laser-produced plasma to maximize throughput; alignment tolerances were established by ray tracing. The streak camera produced single-shot, time-resolved spectra, heavily sloped due to photon time-of-flight differences, with sufficient reproducibility to accumulate photon statistics. The images are time-calibrated by the slope of streaked spectra and dewarped to generate spectra emitted at different times defined at the source. The streaked spectra demonstrate the evolution of spectral shoulders and other features on ps timescales, showing the feasibility of plasma parameter measurements on the rapid timescales necessary to study high-energy-density plasmas. [ABSTRACT FROM AUTHOR]

X-ray ray tracing is used to develop ion-temperature corrections for the analysis of the X-ray Imaging Crystal Spectrometer (XICS) used at Wendelstein 7-X (W7-X) and perform verification on the analysis methods. The XICS is a powerful diagnostic able to measure ion-temperature, electron-temperature, plasma flow, and impurity charge state densities. While these systems are relatively simple in design, accurate characterization of the instrumental response and validation of analysis techniques are difficult to perform experimentally due to the requirement of extended x-ray sources. For this reason, a ray tracing model has been developed that allows characterization of the spectrometer and verification of the analysis methods while fully considering the real geometry of the XICS system and W7-X plasma. Through the use of ray tracing, several important corrections have been found that must be accounted for in order to accurately reconstruct the ion-temperature profiles. The sources of these corrections are described along with their effect on the analyzed profiles. The implemented corrections stem from three effects: (1) effect of sub-pixel intensity distribution during de-curving and spatial binning, (2) effect of sub-pixel intensity distribution during forward model evaluation and generation of residuals, and (3) effect of defocus and spherical aberrations on the instrumental response. Possible improvements to the forward model and analysis procedures are explored, along with a discussion of trade-offs in terms of computational complexity. Finally, the accuracy of the tomographic inversion technique in stellarator geometry is investigated, providing for the first time a verification exercise for inversion accuracy in stellarator geometry and a complete XICS analysis tool-chain. [ABSTRACT FROM AUTHOR]

Fine-structure x-ray spectra have been measured from foils with embedded tracer layers at two laser facilities. A suite of layered foils with thin Ti tracers under varied tamper layers was studied at both the Titan and the ALEPH 400 nm laser facilities, where Ti Heα emission was recorded using a high-resolution Bragg crystal spectrometer. Several indicators of plasma parameters are examined in the spectra, including temperature- and density-dependent line ratios and line broadening from Stark and opacity effects. Spectra indicate that (1) the plasma density at ALEPH is significantly higher than at Titan and (2) the electron temperature is high for near-surface layers at both facilities but drops more quickly with depth at ALEPH. These inferences of plasma conditions are consistent with differing levels of temporal contrast at each laser facility. [ABSTRACT FROM AUTHOR]

Adapting a concept developed for magnetic confinement fusion experiments, an imaging crystal spectrometer has been designed and tested for HED plasmas. The instrument uses a spherically bent quartz [211] crystal with radius of curvature of 490.8 mm. The instrument was tested at the Titan laser at Lawrence Livermore National Laboratory by irradiating titanium slabs with laser intensities of 1019-1020 W/cm². He-like and Li-like Ti lines were recorded, from which the spectrometer performance was evaluated. This spectrometer provides very high spectral resolving power (E/dE > 7000) while acquiring a one-dimensional image of the source. [ABSTRACT FROM AUTHOR]

This research describes advancements in the spectral analysis and error propagation techniques associated with x-ray imaging crystal spectroscopy (XICS) that have enabled this diagnostic to be used to accurately constrain particle, momentum, and heat transport studies in a tokamak for the first time. Doppler tomography techniques have been extended to include propagation of statistical uncertainty due to photon noise, the effect of non-uniform instrumental broadening as well as flux surface variations in impurity density. These methods have been deployed as a suite of modeling and analysis tools, written in interactive data language (IDL) and designed for general use on tokamaks. Its application to the Alcator C-Mod XICS is discussed, along with novel spectral and spatial calibration techniques. Example ion temperature and radial electric field profiles from recent I-mode plasmas are shown, and the impact of poloidally asymmetric impurity density and natural line broadening is discussed in the context of the planned ITER x-ray crystal spectrometer. [ABSTRACT FROM AUTHOR]

A high-resolution x-ray imaging crystal spectrometer, whose concept was tested on NSTX and Alcator C-Mod, is being designed for the large helical device (LHD). This instrument will record spatially resolved spectra of helium-like Ar16+ and will provide ion temperature profiles with spatial and temporal resolutions of <2 cm and ≥10 ms, respectively. The spectrometer layout and instrumental features are largely determined by the magnetic field structure of LHD. The stellarator equilibrium reconstruction codes, STELLOPT and PIES, will be used for the tomographic inversion of the spectral data. [ABSTRACT FROM AUTHOR]

A high resolution (λ/Δλ∼2000) soft x-ray spectrometer has been installed on the Alcator C-Mod tokamak. The system was designed to measure emission line spectra from heliumlike neon (1s12p1→1s2) in a narrow spectral band centered on λ=13.5 Å (920 eV). The instrument is mounted with a poloidal view 20 cm below the midplane (r/a∼0.85). In addition to the neon emission lines, strong fluorine, xenon, iron, and manganese lines have been observed. [ABSTRACT FROM AUTHOR]

The paper describes a new scheme for wide-angle point-to-point x-ray imaging with almost arbitrarily large angles of incidence by a matched pair of spherically bent crystals to eliminate the astigmatism, which is a well-known imaging error of spherical mirrors. In addition to x rays, the scheme should be applicable to a very broad spectrum of the electromagnetic radiation, including microwaves, infrared and visible light, as well as UV and extreme UV radiation, if the crystals are replaced with appropriate spherical reflectors. The scheme may also be applicable to the imaging with ultrasound. [ABSTRACT FROM AUTHOR]

A spectral resolution measurement of the x-ray imaging crystal spectrometer for the Korea Superconducting Tokamak Advanced Research machine utilizing a segmented position-sensitive detector and time-to-digital converter based delay-line readout electronics was performed by using an x-ray tube in a laboratory. The measured spectral resolution is about 12 600, which means the actual energy resolution is 0.32 eV for the x-ray tube’s bremsstrahlung peak energy of 4 keV. The results from the spectral resolution measurement are described. [ABSTRACT FROM AUTHOR]

We describe upgrades to a compact grazing-incidence spectrometer utilized on the National Spherical Torus Experiment for monitoring light and heavy impurities. A fast-readout charge couple device camera has been implemented that allows the recording of spectra with up to 25 ms time integration. This capability is used to study the time evolution of the K-shell emission of hydrogenlike and heliumlike boron, carbon, nitrogen, and oxygen between 10 and 65 Å. Different camera positioning pieces have been employed to extend the possible spectral range to as high as 140. Several lines that cannot be ascribed to the usual elements found in the plasma have been observed in this spectral range, although often only in a few isolated discharges. [ABSTRACT FROM AUTHOR]

A least-squares fit analysis program is being developed for the study of spatially resolved x-ray spectra from tokamak plasmas. The program, written in interactive data language, can handle analysis of spectra from multiple sightlines through the plasma and compare the experimental data with a least-square fit of synthetic spectra, which are constructed from atomic modeling codes. The input parameters such as shot numbers, time groups, spatial range, spectral lines to fit and fitting parameters can be entered interactively through a graphical user interface or automatically via a script. The output consists of graphical presentations of the obtained spectral fits and fit parameter profiles as a function of time, including ion and electron temperature profiles, which are of particular interest. Output can also be sent to any open database connectivity compliant database. The features of the program are demonstrated with the analysis of the spectra of helium-like ArXVII, which were obtained with a new x-ray imaging crystal spectrometer. [ABSTRACT FROM AUTHOR]

A vertically viewing x-ray imaging system (XIS) has been designed to complement the existing 64-channel horizontal system on the tokamak fusion test reactor (TFTR) and enhance measurements of soft x-ray emissivity, plasma (major) radial position, and magnetohydrodynamic (MHD) phenomena. System parameters have been selected to provide adequate signal strength and spatial resolution while permitting a substantial size and cost reduction with respect to the horizontal system. The compact, helium filled x-ray camera employs four eight-channel silicon detector modules and views the plasma through a 3-mil-thick beryllium window, providing 6-cra position resolution at the center. An x-ray absorber foil changer permits energy selection to match the horizontal. XIS. Lead and hydrogenous shielding reduce noise from thermonuclear neutrons and associated gamma rays. [ABSTRACT FROM AUTHOR]

Metal impurity concentrations are measured by the pulse-height-analyzer (PHA) diagnostic from Kα x-ray peak intensities by use of an averaged excitation rate 〈συ〉. Low-Z impurity concentrations are inferred from the continuum enhancement (relative to a pure plasma) minus the enhancement due to metals. Since the PHA does not resolve lines from different charge states, 〈συ〉 is a weighted sum of rates; coronal equilibrium is usually assumed. The 〈συ〉 used earlier omitted the intercombination and forbidden lines from the dominant heliumlike state. The result was an overestimate of metals and an underestimate of low-Z impurities in cases where metals were significant. Improved values of 〈συ〉 using recent calculations for H-, He-, and Li-like Fe range from 10% to 50% larger than the earlier rates and yield metal concentrations in better agreement with those from vacuum ultraviolet (VUV) spectroscopy. [ABSTRACT FROM AUTHOR]

The TFTR x-ray imaging system (XIS) is an array of 64-Si surface barrier diodes which image the plasma poloidally. Special absorber foils have been installed to permit measurement of electron temperature T[sub e] with < 100-µs time resolution along 10-30 chords. The technique uses the ratio of x-ray fluxes transmitted through two different foils, which depend mainly on T[sub e]. Simulations show that strong line radiation can change this ratio. To correct for these effects, special beryllium-scandium filters are employed to select the line-free region between 2 and 4.5 keV. Separate filter pairs allow correction for strong L line radiation as well as Ti or Ni Kα emission. The T[sub e] determination is based on simulations. Comparison of results with T[sub e] values from the electron-cyclotron emission and x-ray pulse height analysis diagnostics is presented. [ABSTRACT FROM AUTHOR]

This paper describes a new x-ray scheme for stigmatic imaging. The scheme consists of one convex spherically bent crystal and one concave spherically bent crystal. The radii of curvature and Bragg reflecting lattice planes of the two crystals are properly matched to eliminate the astigmatism, so that the conditions for stigmatic imaging are met for a particular wavelength. The magnification is adjustable and solely a function of the two Bragg angles or angles of incidence. Although the choice of Bragg angles is constrained by the availability of crystals, this is not a severe limitation for the imaging of plasmas, since a particular wavelength can be selected from the bremsstrahlung continuum. The working principle of this imaging scheme has been verified with visible light. Further tests with x rays are planned for the near future. [ABSTRACT FROM AUTHOR]

A new energy resolving x-ray pinhole camera has been recently installed on Alcator C-Mod. This diagnostic is capable of 1D or 2D imaging with a spatial resolution of ≈1 cm, an energy resolution of ≈1 keV in the range of 3.5-15 keV and a maximum time resolution of 5 ms. A novel use of a Pilatus 2 hybrid-pixel x-ray detector [P. Kraft et al., J. Synchrotron Rad. 16, 368 (2009)] is employed in which the lower energy threshold of individual pixels is adjusted, allowing regions of a single detector to be sensitive to different x-ray energy ranges. Development of this new detector calibration technique was done as a collaboration between PPPL and Dectris Ltd. The calibration procedure is described, and the energy resolution of the detector is characterized. Initial data from this installation on Alcator C-Mod is presented. This diagnostic provides line-integrated measurements of impurity emission which can be used to determine impurity concentrations as well as the electron energy distribution. [ABSTRACT FROM AUTHOR]