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Bayesian inference applied to x-ray spectroscopy data analysis enables uncertainty quantification necessary to rigorously test theoretical models. However, when comparing to data, detailed atomic physics and radiation transfer calculations of x-ray emission from non-uniform plasma conditions are typically too slow to be performed in line with statistical sampling methods, such as Markov Chain Monte Carlo sampling. Furthermore, differences in transition energies and x-ray opacities often make direct comparisons between simulated and measured spectra unreliable. We present a spectral decomposition method that allows for corrections to line positions and bound–bound opacities to best fit experimental data, with the goal of providing quantitative feedback to improve the underlying theoretical models and guide future experiments. In this work, we use a neural network (NN) surrogate model to replace spectral calculations of isobaric hot-spots created in Kr-doped implosions at the National Ignition Facility. The NN was trained on calculations of x-ray spectra using an isobaric hot-spot model post-processed with Cretin, a multi-species atomic kinetics and radiation code. The speedup provided by the NN model to generate x-ray emission spectra enables statistical analysis of parameterized models with sufficient detail to accurately represent the physical system and extract the plasma parameters of interest. [ABSTRACT FROM AUTHOR]

A new class of crystal shapes has been developed for x-ray spectroscopy of point-like or small (a few mm) emission sources. These optics allow for dramatic improvement in both achievable energy resolution and total throughput of the spectrometer as compared with traditional designs. This class of crystal shapes, collectively referred to as the Variable-Radii Spiral (VR-Spiral), utilize crystal shapes in which both the major and minor radii are variable. A crystal using this novel VR-Spiral shape has now been fabricated for high-resolution Extended X-ray Absorption Fine Structure (EXAFS) experiments targeting the Pb-L3 (13.0 keV) absorption edge at the National Ignition Facility. The performance of this crystal has been characterized in the laboratory using a microfocus x-ray source, showing that high-resolution high-throughput EXAFS spectra can be acquired using this geometry. Importantly, these successful tests show that the complex three-dimensional crystal shape is manufacturable with the required precision needed to realize the expected performance of better than 5 eV energy resolution while using a 30 mm high crystal. An improved generalized mathematical form for VR-Spiral shapes is also presented allowing improved optimization as compared to the first sinusoidal-spiral based design. This new formulation allows VR-Spiral spectrometers to be designed at any magnification with optimized energy resolution at all energies within the spectrometer bandwidth. [ABSTRACT FROM AUTHOR]

A new x-ray imaging crystal spectrometer is developed for time-resolved measurements of x-ray line spectra. One of the main advantages is that it produces perfect images of a point source for each wavelength in a selectable spectral range. The other advantage is that the detector plane can have an arbitrary orientation with respect to the crystal surface. These unique imaging properties are obtained by bending the crystal into a certain shape, which is generated by arranging multiple cones from different aperture angles on a common nodal line. The test results were presented from optical tests of the multi-cone and single-cone structures. The numerical results on the deteriorations of the spectral and spatial resolutions are obtained due to the potential misalignments of the source. The concept of the configuration is considered to be particularly useful for high-power laser experiments where the size of the source is small and a wide spectral range would be diagnosed. [ABSTRACT FROM AUTHOR]

Imaging x-ray crystal spectrometer (XCS) arrays are being developed as a US-ITER activity for Doppler measurement of Ti and v profiles of impurities (W, Kr, and Fe) with ∼7 cm (a/30) and 10-100 ms resolution in ITER. The imaging XCS, modeled after a prototype instrument on Alcator C-Mod, uses a spherically bent crystal and 2D x-ray detectors to achieve high spectral resolving power (E/dE>6000) horizontally and spatial imaging vertically. Two arrays will measure Ti and both poloidal and toroidal rotation velocity profiles. The measurement of many spatial chords permits tomographic inversion for the inference of local parameters. The instrument design, predictions of performance, and results from C-Mod are presented. [ABSTRACT FROM AUTHOR]

We describe the anticipated performance of an x-ray microcalorimeter instrument on ITER. As part of the core imaging x-ray spectrometer, the instrument will augment the imaging crystal spectrometers by providing a survey of the concentration of heavy ion plasma impurities in the core and possibly ion temperature values from the emission lines of different elemental ions located at various radial positions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (λ/dλ>6000) of He-like and H-like Ar Kα lines with good spatial (∼1 cm) and temporal (∼10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (Ti), and toroidal plasma rotation velocity (v[lowercase_phi_synonym]) from the line Doppler widths and shifts. The data analysis techniques, Ti and v[lowercase_phi_synonym] profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented. [ABSTRACT FROM AUTHOR]

The use of high resolution x-ray crystal spectrometers to diagnose fusion plasmas has been limited by the poor spatial localization associated with chord integrated measurements. Taking advantage of a new x-ray imaging spectrometer concept [M. Bitter et al., Rev. Sci. Instrum. 75, 3660 (2004)], and improvements in x-ray detector technology [Ch. Broennimann et al., J. Synchrotron Radiat. 13, 120 (2006)], a spatially resolving high resolution x-ray spectrometer has been built and installed on the Alcator C-Mod tokamak. This instrument utilizes a spherically bent quartz crystal and a set of two dimensional x-ray detectors arranged in the Johann configuration [H. H. Johann, Z. Phys. 69, 185 (1931)] to image the entire plasma cross section with a spatial resolution of about 1 cm. The spectrometer was designed to measure line emission from H-like and He-like argon in the wavelength range 3.7 and 4.0 Å with a resolving power of approximately 10 000 at frame rates up to 200 Hz. Using spectral tomographic techniques [I. Condrea, Phys. Plasmas 11, 2427 (2004)] the line integrated spectra can be inverted to infer profiles of impurity emissivity, velocity, and temperature. From these quantities it is then possible to calculate impurity density and electron temperature profiles. An overview of the instrument, analysis techniques, and example profiles are presented. [ABSTRACT FROM AUTHOR]

A new type of high-resolution x-ray imaging crystal spectrometer is being developed to measure ion and electron temperature profiles in tokamak plasmas. The instrument is particularly valuable for diagnosing plasmas with purely ohmic heating and rf heating, since it does not require the injection of a neutral beam—although it can also be used for the diagnosis of neutral-beam heated plasmas. The spectrometer consists of a spherically bent quartz crystal and a two-dimensional position-sensitive detector. It records spectra of helium-like argon (or krypton) from multiple sightlines through the plasma and projects a de-magnified image of a large plasma cross section onto the detector. The spatial resolution in the plasma is solely determined by the height of the crystal, its radius of curvature, and the Bragg angle. This new x-ray imaging crystal spectrometer may also be of interest for the diagnosis of ion temperature profiles in future large tokamaks, the Korea Superconducting Tokamak Advanced Research tokamak and the International Thermonuclear Experimental Reactor, where the application of the presently used charge-exchange spectroscopy will be difficult, if the neutral beams do not penetrate to the plasma center. The article presents the results from proof-of-principle experiments performed with a prototype instrument at Alcator C-Mod. [ABSTRACT FROM AUTHOR]

Two x-ray imaging crystal spectrometers are presently designed for the KSTAR tokamak. The instruments will provide temporally and spatially resolved spectra of heliumlike argon (or krypton) from a large cross section of the plasma. The spectral data will be used for profile measurements— both within and perpendicular to the horizontal midplane of KSTAR—of the ion and electron temperatures, the rotation velocity, and the ionization equilibrium. Each spectrometer will consist of a spherically bent quartz crystal and large area two-dimensional position-sensitive multiwire proportional counter. The article presents the design for the KSTAR x-ray imaging crystal spectrometers, and the fabrication and initial test results from the large area two-dimensional multiwire proportional counter. [ABSTRACT FROM AUTHOR]

A detector setup with three LN-cooled Si(Li) diodes is used to measure soft x-ray spectra (0.8–20 keV) emitted from the inside walls of the PDX vessel during the plasma discharge. The setup is part of a pulse-height-analysis system, which is used to measure the plasma and wall radiation simultaneously at five different radial positions. The wall and the plasma radiation are measured under different plasma conditions (e.g., OH and neutral beam heating). The wall radiation is very much increased during the neutral beam heating, with an enhancement factor of at least 10 over the OH wall radiation. Since we measure the plasma and the wall radiation at the same time, the measurements allow the conclusion that the wall radiation can be attributed essentially to fluorescence (line radiation, e.g., Ti-Kα) and scattering (continuum part of the wall radiation spectrum). The fluorescence and the scattering are both caused by soft x-ray radiation flux coming from the plasma. There seems to be no need to invoke other, more exotic causes for the wall radiation, for example, charge particle bombardment of the wall. [ABSTRACT FROM AUTHOR]

X-ray spectroscopy of mid-Z metal impurities is important in the study of tokamak plasmas and may reveal potential problems if their contribution to the radiated power becomes substantial. The analysis of the data from a high-resolution x-ray and extreme ultraviolet grating spectrometer, XEUS, installed on NSTX, was performed focused on a detailed study of x-ray spectra in the range 7-18 Å. These spectra include not only commonly seen iron spectra but also copper spectra not yet employed as an NSTX plasma impurity diagnostic. In particular, the L-shell Cu spectra were modeled and predictions were made for identifying contributions from various Cu ions in different spectral bands. Also, similar spectra, but from much denser Cu plasmas produced on the UNR Z-pinch facility and collected using the convex-crystal spectrometer, were analyzed and compared with NSTX results. [ABSTRACT FROM AUTHOR]

New x-ray imaging crystal spectrometers, currently operating on Alcator C-Mod, NSTX, EAST, and KSTAR, record spectral lines of highly charged ions, such as Ar16+, from multiple sightlines to obtain profiles of ion temperature and of toroidal plasma rotation velocity from Doppler measurements. In the present work, we describe a new data analysis routine, which accounts for the specific geometry of the sightlines of a curved-crystal spectrometer and includes corrections for the Johann error to facilitate the tomographic inversion. Such corrections are important to distinguish velocity induced Doppler shifts from instrumental line shifts caused by the Johann error. The importance of this correction is demonstrated using data from Alcator C-Mod. [ABSTRACT FROM AUTHOR]

A high-resolution spectrometer for measuring the soft x-ray emission (7-24 Å) has been implemented on the National Spherical Tokamak Experiment (NSTX). The instrument will be used to study the K-shell spectra of O, Ne, and Mg as well as the L-shell spectra of Fe and Ni and to calibrate spectral diagnostics of fusion and astrophysical plasmas. The spectrometer employs a spherically bent crystal for dispersion and two microchannel-plate intensified 1D charged-coupled devices for recording the x rays. The temporal resolution is 25 ms per spectrum. [ABSTRACT FROM AUTHOR]

X-ray spectra obtained with position-sensitive detectors which use delay-line readout systems are subject to distortions at comet rares comparable to the inverse of the temporal length of the delay line. These distortions are due to the simultaneous existence of pulses from different photons on the delay line. High incident rates up to several MHz can be obtained on the detectors of the TFTR crystal spectrometer under certain conditions. This paper describes improvements which can be obtained by an interarrival time discriminator circuit. [ABSTRACT FROM AUTHOR]

A Bragg x-ray spectrometer of high spectral resolution (λ/Δλ = 10 000-20 000) which accommodates three crystals and position-sensitive detectors in the Johann configuration has been installed in the diagnostic basement of the tokamak fusion test reactor (TFTR) for the measurement of radial ion temperature profiles. The ion temperature is derived from the Doppler broadening of Kα-resonance lines of metal impurity ions, e.g., Ti, Cr, Fe, and Ni, in the heliumlike and hydrogen-like charge states. The x-ray diffraction plane is almost perpendicular to the magnetic axis, but slightly tilted by an angle of 3.8°, which makes it possible to measure poloidal and toroidal plasma rotation velocities of ye > 5 × 10³ m/s and v[sub φ] > 1 × 10[sup 5] m/s, from the Doppler shift of spectral lines. Results obtained from the observation of TiXX1 Kα-line spectra with a 220-silicon crystal ora 2d spacing of 3.8400 Å and a curvature radius of 11.05 m are reported. [ABSTRACT FROM AUTHOR]

The x-ray pulse-height analysis (PHA) diagnostic uses a liquid-nitrogen cooled array of 5 Si(Li) and one HpGe detectors to do time-resolved (5-100 ms) x-ray spectroscopy of the central horizontal chord of the Tokamak Fusion Test Reactor (TFTR) plasmas in the 1-50-keV range. Central electron temperature T[sub e] and concentration of medium and low-Z impurities are derived from the spectra. Remotely selectable absorber-foil arrays provide selection of the energy range. Fixed and movable aperture arrays allow approximate equalization of count rates in different energy bands and extend dynamic range. Amplifier pulse shapes are approximately triangular. Main amplifier peaking time is 4 µs yielding 230-eV FWHM at 5.9 keV. Pileup inspection times are selectable at 0.13, 0.4, or 0.9 µs. Throughput is up to 42 kHz. The PHA has been used to study temperature and impurities over a wide range of TFTR operational parameters. Dramatic variations in metal impurities with density, plasma current, and major radius have been observed. [ABSTRACT FROM AUTHOR]

Measurements are presented on the contributions from dielectronic satellite transitions from upper configurations 1s2lnl', n≥3 to the characteristic x-ray emission of heliumlike Fe[sup 24+]. The measurements were carried out on the electron beam ion trap at Livermore using high-resolution Bragg-crystal spectroscopy. By eliminating uncertainties in the location and magnitude of the satellite contributions inherent in theoretical predictions the measurements improve the use of the resonance line emission of heliumlike Fe[sup 24+] as a diagnostic of ion temperature and rotation velocity of high-temperature plasmas. [ABSTRACT FROM AUTHOR]

An array of 64 silicon surface-barrier diodes on a circular arc view Tokamak Fusion Test Reactor (TFTR) plasmas through a slot aperture to provide poloidal imaging of x-ray emission in the 200 eV-15 keV range. Information is inferred on magnetohydrodynamic (MHD) instabilities, disruptions, radiation, impurity transport, electron temperature., and electron thermal conductivity. Spatial resolution is 2.5 cm. Movable absorber foil arrays provide energy selection. Preamplifier-amplifier pairs have gains of 0.05-100 V/µA. Two outputs are provided with (1) 40-, 80-, and 300-Hz and (2) 40-, 80-, and 600-kHz filtering. The signals are digitized at rates up to 500 kHz and stored in 128 K (total system) memory. Foils, gains, and filters are selectable from the control room by a computer. [ABSTRACT FROM AUTHOR]

High resolution (λ/Δλ ∼ 10 000) 1D imaging x-ray spectroscopy using a spherically bent crystal and a 2D hybrid pixel array detector is used world wide for Doppler measurements of ion-temperature and plasma flow-velocity profiles in magnetic confinement fusion plasmas. Meter sized plasmas are diagnosed with cm spatial resolution and 10 ms time resolution. This concept can also be used as a diagnostic of small sources, such as inertial confinement fusion plasmas and targets on x-ray light source beam lines, with spatial resolution of micrometers, as demonstrated by laboratory experiments using a 250-μm 55Fe source, and by ray-tracing calculations. Throughput calculations agree with measurements, and predict detector counts in the range 10-8-10-6 times source x-rays, depending on crystal reflectivity and spectrometer geometry. Results of the lab demonstrations, application of the technique to the National Ignition Facility (NIF), and predictions of performance on NIF will be presented. [ABSTRACT FROM AUTHOR]

A high vacuum x-ray crystal spectrometer was fabricated utilizing a large spherically bent mica crystal (2 cm×7 cm) and a x-ray sensitive charge coupled device camera to observe heliumlike neon spectra in the wavelength range from 13.4474 to 13.6980 A and heliumlike spectra of other low-Z elements, such as Mg and Al. The spectrometer was specifically designed for use at a low x-ray intensity magnetic mirror machine. The x-ray imaging characteristics of the large spherically bent mica crystal have been tested in the laboratory with an x-ray source, using the bremsstrahlung continuum. The results of these calibration measurements will be presented. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The TFTR horizontal x-ray crystal spectrometer has been improved by installation of γ and neutron shielding and is now operating in the TFTR Test Cell up to the presently maximum neutron production rates of 2 × 10[sup 16] neutrons/s. Further optimization by using a modified detector may assure operation of the spectrometer during the DT phase when TFTR is covered by an igloo. The instrument is set up for simultaneous observation of the entire satellite spectrum of Ni XXVII, and it provides data on the time evolution of the central ion temperature and the central plasma rotation velocity. Ion temperatures of 20-30 keV have been measured under "supershot" conditions. The highest rotation velocity observed with unidirectional injection was 1.1 × 10[sup 6] m/s. [ABSTRACT FROM AUTHOR]

Abstract: Enhanced confinement regimes with steep gradients of density profiles and the need to place rotation velocity profiles call for maximum spatial resolution in the tokamak plasma. It is proposed to achieve such a resolution by using X-ray spectroscopy with double reflections in single crystals. [Copyright &y& Elsevier]