Search

The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for future spherical torus (ST) devices and ITER. Plasma durations up to 1.6 s (five current redistribution times) have been achieved at plasma currents of 0.7 MA with non-inductive current fractions above 65% while simultaneously achieving βT and βN values of 17% and 5.7 (%m T MA-1), respectively. A newly available motional Stark effect diagnostic has enabled validation of current-drive sources and improved the understanding of NSTX 'hybrid'-like scenarios. In MHD research, ex-vessel radial field coils have been utilized to infer and correct intrinsic EFs, provide rotation control and actively stabilize the n ≤ 1 resistive wall mode at ITER-relevant low plasma rotation values. In transport and turbulence research, the low aspect ratio and a wide range of achievable β in the NSTX provide unique data for confinement scaling studies, and a new microwave scattering diagnostic is being used to investigate turbulent density fluctuations with wavenumbers extending from ion to electron gyro-scales. In energetic particle research, cyclic neutron rate drops have been associated with the destabilization of multiple large toroidal Alfven eigenmodes (TAEs) analogous to the 'sea-of-TAE' modes predicted for ITER, and three-wave coupling processes have been observed for the first time. In boundary physics research, advanced shape control has enabled studies of the role of magnetic balance in H-mode access and edge localized mode stability. Peak divertor heat flux has been reduced by a factor of 5 using an H-mode-compatible radiative divertor, and lithium conditioning has demonstrated particle pumping and results in improved thermal confinement. Finally, non-solenoidal plasma start-up experiments have achieved plasma currents of 160 kA on closed magnetic flux surfaces utilizing coaxial helicity injection. © 2007 IAEA.

Research on the spherical torus (or spherical tokamak) (ST) is being pursued to explore the scientific benefits of modifying the field line structue fro that in more moderate aspect ratio devices. The ST experiments are being conducted in various US research facilities. The area of power and particle handling is expected to be challenging because of the higher power density expected in the ST relative to that in conventional aspect-ratio tokamaks.

A major research goal of the national spherical torus experiment is establishing long-pulse, high beta, high confinement operation and its physics basis. This research has been enabled by facility capabilities developed during 2001 and 2002, including neutral beam (up to 7 MW) and high harmonic fast wave (HHFW) heating (up to 6 MW), toroidal fields up to 6 kG, plasma currents up to 1.5 MA, flexible shape control, and wall preparation techniques. These capabilities have enabled the generation of plasmas with βT ≡ /(BT02/2μ0) of up to 35%. Normalized beta values often exceed the no-wall limit, and studies suggest that passive wall mode stabilization enables this for H mode plasmas with broad pressure profiles. The viability of long, high bootstrap current fraction operations has been established for ELMing H mode plasmas with toroidal beta values in excess of 15% and sustained for several current relaxation times. Improvements in wall conditioning and fuelling are likely contributing to a reduction in H mode power thresholds. Electron thermal conduction is the dominant thermal loss channel is auxiliary heated plasmas examined thus far. HHFW effectively heats electrons, and its acceleration of fast beam ions has been observed. Evidence for HHFW current drive is obtained by comparison of the loop voltage evolution in plasmas with matched density and temperature profiles but varying phases of launched HHFW waves. Studies of emissions from electron Bernstein waves indicate a density scale length dependence of their transmission across the upper hybrid resonance near the plasma edge that is consistent with theoretical predictions. A peak heat flux to the divertor targets of 10 MW m-2 has been measured in the H mode, with large asymmetries being observed in the power deposition between the inner and outer strike points. Non-inductive plasma startup studies have focused on coaxial helicity injection. With this technique, toroidal currents up to 400 kA have been driven, and studies to assess flux closure and coupling to other current drive techniques have begun.

The Tokamak Fusion Test Reactor (TFTR) is a large tokamak which has performed experiments with 50:50 deuterium-tritium fuelled plasmas. Since 1993, TFTR has produced about 1090 D-T plasmas using about 100 grams of tritium and producing about 1.6 GJ of D-T fusion energy. These plasmas have significant populations of 3.5 MeV alphas (the charged D-T fusion product). TFTR research has focused on alpha particle confinement, alpha driven modes, and alpha heating studies. Maximum D-T fusion power production has aided these studies, requiring simultaneously operation at high input heating power and large energy confinement time (to produce the highest temperature and density), while maintaining low impurity content. The principal limitation to the TFTR fusion power production was the disruptive stability limit. Secondary limitations were the confinement time, and limiter power handling capability. © 1997 IOP Publishing Ltd.

Experiments in the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 2, 2176 (1995)] have explored several novel regimes of improved tokamak confinement in deuterium–tritium (D–T) plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region (high [formula omitted]). New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA [formula omitted] accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-[formula omitted] plasmas produced by rapid expansion of the minor cross section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D–T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D–T plasmas with [formula omitted] and weak magnetic shear in the central region, a toroidal Alfvén eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions. © 1997, American Institute of Physics. All rights reserved.

Experiments with plasmas having nearly equal concentrations of deuterium and tritium have been carried out on TFTR. To date (September 1995), the maximum fusion power has been 10.7 MW, using 39.5 MW of neutral beam heating, in a supershot discharge and 6.7 MW in a high beta P discharge following a current ramp-down. The fusion power density in the core of the plasma has reached 2.8 MW/m3, exceeding that expected in the International Thermonuclear Experimental Reactor (ITER). The energy confinement time tau E is observed to increase in DT, relative to D plasmas, by 20% and the n1(0).T1(0). tau E product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter H mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high beta P discharges. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP simulations assuming classical confinement. Measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from helium gas puffing experiments. The loss of energetic alpha particles to a detector at the bottom of the vessel is well described by the first-orbit loss mechanism. No loss due to alpha particle driven instabilities has yet been observed. ICRF heating of a DT plasma, using the second harmonic of tritium, has been demonstrated. DT experiments on TFTR will continue both to explore the physics underlying the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor.

Routine tritium operation in TFTR has permitted investigations of alpha particle physics in parameter ranges resembling those of a reactor core. ICRF wave physics in a DT plasma and the influence of isotopic mass on supershot confinement have also been studied. Continued progress has been made in optimizing fusion power production in TFTR, using extended machine capability and Li wall conditioning. Performance is currently limited by MHD stability. A new reversed magnetic shear regime is being investigated with reduced core transport and a higher predicted stability limit.

TFTR has begun its campaign to study deuterium-tritium fusion under reactor-like conditions. Variable amounts of deuterium and tritium neutral beam power have been used to maximize fusion power, study alpha heating, investigate alpha particle confinement, and search for alpha driven plasma instabilities. Additional areas of study include energy and particle transport and confinement, ICRF heating schemes for DT plasmas, tritium retention, and fusion in high βp plasmas. The majority of this work is done in the TFTR supershot confinement regime. To obtain supershots, extensive limiter conditioning using helium fueled ohmic discharges and lithium pellet injection into ohmic and neutral beam heated plasmas is performed, resulting in a low recycling limiter. The relationship between recycling and core plasma confinement has been studied by using helium, deuterium and high-Z gas puffs to simulate high recycling limiter conditions. These studies show that confinement in TFTR supershots is very sensitive to the influx of neutral particles at the plasma edge. © 1995, All rights reserved.

Three campaigns, prior to July 1994, attempted to increase the fusion power in DT plasmas on the Tokamak Fusion Test Reactor (TFTR). The first campaign was dedicated to obtaining >5 MW of fusion power while avoiding MHD events similar to the JET X-event. The second was aimed at producing maximum fusion power irrespective of proximity to MHD limits, and achieved 9 MW limited by a disruption. The third campaign increased the energy confinement time using lithium pellet conditioning while raising the ratio of alpha heating to beam heating.

The Tomamak Fusion Test reactor has performed initial high-power experiments with the plasma fueled with nominally equal densities of deuterium and tritium. Compared to pure deuterium plasmas, the energy stored in the electron and ions increased by ∼20%. These increases indicate improvements in confinement associated with the use of tritium and possibly heating of electrons by α particles created by the D-T fusion reactions. © 1994 The American Physical Society.

Peak fusion power production of 6.2±0.4 MW has been achieved in TFTR plasmas heated by deuterium and tritium neutral beams at a total power of 29.5 MW. These plasmas have an inferred central fusion alpha particle density of 1.2×1017 m-3 without the appearance of either disruptive magnetohydrodynamics events or detectable changes in Alfvén wave activity. The measured loss rate of energetic alpha particles agreed with the approximately 5% losses expected from alpha particles which are born on unconfined orbits. © 1994 The American Physical Society.

The final hardware modifications for tritium operation have been completed for the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. These activities include preparation of the tritium gas handling system, installation of additional neutron shielding, conversion of the toroidal field coil cooling system from water to a Fluorinert™ system, modification of the vacuum system to handle tritium, preparation, and testing of the neutral beam system for tritium operation and a final deuterium-deuterium (D-D) run to simulate expected deuterium-tritium (D-T) operation. Testing of the tritium system with low concentration tritium has successfully begun. Simulation of trace and high power D-T experiments using D-D have been performed. The physics objectives of D-T operation are production of ≈ 10 MW of fusion power, evaluation of confinement, and heating in deuteriumtritium plasmas, evaluation of α-particle heating of electrons, and collective effects driven by alpha particles and testing of diagnostics for confined a particles. Experimental results and theoretical modeling in support of the D-T experiments are reviewed. © 1994 American Institute of Physics.

A review of TFTR plasma transport studies is presented. Parallel transport and the confinement of suprathermal ions are found to be relatively well described by theory. Cross-field transport of the thermal plasma, however, is anomalous with the momentum diffusivity being comparable to the ion thermal diffusivity and larger than the electron thermal diffusivity in neutral beam heated discharges. Perturbative experiments have studied nonlinear dependencies in the transport coefficients and examined the role of possible nonlocal phenomena. The underlying turbulence has been studied using microwave scattering, beam emission spectroscopy and microwave reflectometry over a much broader range in k perpendicular to than previously possible. Results indicate the existence of large-wavelength fluctuations correlated with enhanced transport.

Tangentially coinjected deuterium beam ions were accelerated from 82 up to 150 keV during a major-radius compression experiment in the tokamak fusion test reactor. The ion energy spectra and the variation in fusion yield were in good agreement with Fokker-Planck code simulations. In addition, the plasma rotation velocity was observed to rise during compression. © 1985 The American Physical Society.

Neutral-beam heating of plasmas in the Tokamak Fusion Test Reactor at low preinjection densities [ne(0)1019 m-3] were characterized by Te(0)=6.5 keV, Ti(0)=20 keV, ne(0)=7×1019 m-3, E=170 msec, theta=2, and a d(d,n)3He neutron emission rate of 1016 sec-1. The ion temperature and the deuterium-fusion neutron yields were significantly higher than for previous tokamak experiments. The low initial densities were achieved by operation of the Tokamak Fusion Test Reactor with low plasma currents (1 MA) and by extensive limiter conditioning. © 1987 The American Physical Society.

High-energy-density laser facilities and advances in dynamic compression techniques have expanded access to material states in the Terapascal regime relevant to inertial confinement fusion, planetary science, and geophysics. However, experimentally determining the material temperature in these extreme conditions has remained a difficult challenge. Extended X-ray Absorption Fine Structure (EXAFS), referring to the modulations in x-ray absorption above an absorption edge from photoelectrons' interactions with neighboring atoms, has proven to be a versatile and robust technique for probing material temperature and density for mid-to-high Z elements under dynamic compression. The current platform at the National Ignition Facility has developed six configurations for EXAFS measurements between 7 and 18 keV for different absorption edges (Fe K, Co K, Cu K, Ta L3, Pb L3, and Zr K) using a curved-crystal spectrometer and a bright, continuum foil x-ray source. In this work, we describe the platform geometry, x-ray source performance, spectrometer resolution and throughput, design considerations, and data in ambient and dynamic-compression conditions., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

X-ray line emission spectra can thoroughly characterize hot plasmas, especially when line shapes and ratios convey distinct aspects of plasma conditions. However, the high spectral resolution required for observing line shapes is often at odds with the large bandwidth required to observe many line ratios across a wide spectral range. One strategy to obtain high spectral resolution over a wide bandwidth is to use multiple crystals with calibrated reflectivity so that line intensities across different crystals can be compared. Here, we explore the use of a low-resolution, wide-bandwidth mica survey spectrometer to infer relative reflectivity of two high-resolution, narrow-bandwidth quartz crystals. A Monte Carlo error analysis determines comparable x-ray line ratios measured from both spectrometers, resulting in an in situ calibration factor and associated uncertainty for the relative reflectivity of the high-resolution crystals., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

X-ray sources for a range of wavelengths are being considered for in situ calibration of X-ray Imaging Crystal Spectrometers (XICSs) and for monitoring line shifts due to changes in the crystal temperature, which can vary during experimental operation over a day [A. Ince-Cushman et al., Rev. Sci. Instrum. 79, 10E302 (2008), L. Delgado-Aparicio et al., Plasma Phys. Control. Fusion 55, 125011 (2013)]. Such crystal temperature dependent shifts, if not accounted for, could be erroneously interpreted as Doppler shifts leading to errors in plasma flow-velocity measurements. The x-ray sources encompass characteristic x-ray lines falling within the wavelength range of 0.9-4.0 Å, relevant for the XICSs on present and future fusion devices. Several technological challenges associated with the development of x-ray sources for in situ calibration are identified and are being addressed in the design of multiple x-ray tubes, which will be installed inside the spectrometer housing of the XICS for the JT-60SA tokamak. These x-ray sources will be especially useful for in situ calibration between plasma discharges. In this paper, laboratory experiments are described that were conducted with a Cu x-ray source, a heated quartz (102) crystal, and a pixelated Pilatus detector to measure the temperature dependent shifts of the Cu Kα1 and Kα2 lines at 1.5405 and 1.5443 Å, respectively, and to evaluate the 2d-lattice constant for the Bragg reflecting crystal planes as a function of temperature, which, in the case of in situ wavelength calibration, would have to be used for numerical analysis of the x-ray spectra from the plasma., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

A powerful and flexible hard x-ray (HXR) camera has been recently installed and tested on the WEST tokamak (CEA, France) in collaboration with the Princeton Plasma Physics Laboratory. The diagnostic is a pinhole camera fielded with a 2D pixel detector equipped with a 1 mm thick CdTe sensor. The novelty of this diagnostic technique is the detector's capability of adjusting the threshold energy at the pixel level. This innovation provides great flexibility in the energy configuration, allowing simultaneous space, energy, and time resolved x-ray measurements. The novel camera has been used to measure the core radiation from non-Maxwellian (fast) electrons accelerated by Lower Hybrid (LH) waves and also the beam-target emission of tungsten in the divertor region produced by fast electron losses interacting with the target. In addition, anisotropic hard x-ray emission has been detected for the first time at the WEST core and edge plasma, with opposite toroidal intensity trends. Experimental vertical and toroidal HXR profiles have been successfully reproduced with the LH code LUKE., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

A high-fidelity synthetic diagnostic has been developed for the ITER core x-ray crystal spectrometer diagnostic based on x-ray ray tracing. This synthetic diagnostic has been used to model expected performance of the diagnostic, to aid in diagnostic design, and to develop engineering tolerances. The synthetic model is based on x-ray ray tracing using the recently developed xicsrt ray tracing code and includes a fully three-dimensional representation of the diagnostic based on the computer aided design. The modeled components are: plasma geometry and emission profiles, highly oriented pyrolytic graphite pre-reflectors, spherically bent crystals, and pixelated x-ray detectors. Plasma emission profiles have been calculated for Xe44+, Xe47+, and Xe51+, based on an ITER operational scenario available through the Integrated Modelling & Analysis Suite database, and modeled within the ray tracing code as a volumetric x-ray source; the shape of the plasma source is determined by equilibrium geometry and an appropriate wavelength distribution to match the expected ion temperature profile. All individual components of the x-ray optical system have been modeled with high-fidelity producing a synthetic detector image that is expected to closely match what will be seen in the final as-built system. Particular care is taken to maintain preservation of photon statistics throughout the ray tracing allowing for quantitative estimates of diagnostic performance., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

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., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Large laser facilities have recently enabled material characterization at the pressures of Earth and Super-Earth cores. However, the temperature of the compressed materials has been largely unknown, or solely relied on models and simulations, due to lack of diagnostics under these challenging conditions. Here, we report on temperature, density, pressure, and local structure of copper determined from extended x-ray absorption fine structure and velocimetry up to 1 Terapascal. These results nearly double the highest pressure at which extended x-ray absorption fine structure has been reported in any material. In this work, the copper temperature is unexpectedly found to be much higher than predicted when adjacent to diamond layer(s), demonstrating the important influence of the sample environment on the thermal state of materials; this effect may introduce additional temperature uncertainties in some previous experiments using diamond and provides new guidance for future experimental design., (© 2023. The Author(s).)

Solids ablate under laser irradiation, but experiments have not previously characterized the initiation of this process at ultrarelativistic laser intensities. We present first measurements of bulk ion velocity distributions as ablation begins, captured as a function of depth via Doppler-shifted x-ray line emission from two viewing angles. Bayesian analysis indicates that bulk ions are either nearly stationary or flowing outward at the plasma sound speed. The measurements quantitatively constrain the laser-plasma ablation mechanism, suggesting that a steplike electrostatic potential structure drives solid disassembly.

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-L 3 (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.

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.

WEST (tungsten environment in steady-state tokamak) is starting operation for the first time with a water-cooled full tungsten divertor, enabling long pulse operation. Heating is provided by radiofrequency systems, including lower hybrid current drive (LHCD). In this context, a compact multi-energy hard x-ray camera has been installed for energy and space-resolved measurements of the electron temperature, the fast electron tail density produced by LHCD and runaway electrons, and the beam-target emission of tungsten at the target due to fast electron losses interacting with the divertor plates. The diagnostic is a pinhole camera based on a 2D pixel array detector (Pilatus 3 CdTe CMOS Hybrid-Pixel detector produced by DECTRIS). The novelty of this diagnostic technique is the detector's capability of adjusting the threshold energy at pixel level. This innovation provides great flexibility in the energy configuration, allowing simultaneous space and energy-resolved x-ray measurements. This contribution details two important steps in the preparation of the diagnostic operation. First, the in-vessel spatial calibration that was carried out with a radioactive source. Second, the synthetic diagnostic is obtained by the suite of codes ALOHA/C3PO/LUKE/R5-X2, which simulates LH wave propagation and absorption, as well as the fast electron bremsstrahlung production.

Evolution of the hot spot plasma conditions was measured using high-resolution x-ray spectroscopy at the National Ignition Facility. The capsules were filled with DD gas with trace levels of Kr and had either a high-density-carbon (HDC) ablator or a tungsten (W)-doped HDC ablator. Time-resolved measurement of the Kr Heβ spectra, absolutely calibrated by a simultaneous time-integrated measurement, allows inference of the electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. By matching the calculated hot spot emission using a collisional-radiative code to experimental observations, the hot spot size and areal density are determined. These advanced spectroscopy techniques further reveal the effect of W dopant in the ablator on the hot spot parameters for their improved implosion performance.

Heβ spectral line shapes are important for diagnosing temperature and density in many dense plasmas. This work presents Heβ line shapes measured with high spectral resolution from solid-density plasmas with minimized gradients. The line shapes show hallmark features of Stark broadening, including quantifiable redshifts and double-peaked structure with a significant dip between the peaks; these features are compared to models through a Markov chain Monte Carlo framework. Line shape theory using the dipole approximation can fit the width and peak separation of measured line shapes, but it cannot resolve an ambiguity between electron density n_{e} and ion temperature T_{i}, since both parameters influence the strength of quasistatic ion microfields. Here a line shape model employing a full Coulomb interaction for the electron broadening computes self-consistent line widths and redshifts through the monopole term; redshifts have different dependence on plasma parameters and thus resolve the n_{e}-T_{i} ambiguity. The measured line shapes indicate densities that are 80-100% of solid, identifying a regime of highly ionized but well-tamped plasma. This analysis also provides the first strong evidence that dense ions and electrons are not in thermal equilibrium, despite equilibration times much shorter than the duration of x-ray emission; cooler ions may arise from nonclassical thermalization rates or anomalous energy transport. The experimental platform and diagnostic technique constitute a promising new approach for studying ion-electron equilibration in dense plasmas.

A novel high-resolution x-ray spectrometer for point-like emission sources has been developed using a crystal shape having both a variable major and a variable minor radius of curvature. This variable-radii sinusoidal spiral spectrometer (VR-Spiral) allows three common spectrometer design goals to be achieved simultaneously: 1. reduction of aberrations and improved spectral (energy) resolution, 2. reduction of source size broadening, and 3. use of large crystals to improve total throughput. The VR-Spiral concept and its application to practical spectrometer design are described in detail. This concept is then used to design a spectrometer for an extreme extended x-ray absorption fine structure experiment at the National Ignition Facility looking at the Pb L 3 absorption edge at 13.0352 keV. The expected performance of this VR-Spiral spectrometer, both in terms of energy resolution and spatial resolution, is evaluated through the use of a newly developed raytracing tool, xicsrt. Finally, the expected performance of the VR-Spiral concept is compared to that of spectrometers based on conventional toroidal and variable-radii toroidal crystal geometries showing a greatly improved energy resolution.

We report the development of a high-resolution spectrometer for extended x-ray absorption fine structure (EXAFS) studies of materials under extreme conditions. A curved crystal and detector in the spectrometer are replaceable such that a single body is employed to perform EXAFS measurements at different x-ray energy intervals of interest. Two configurations have been implemented using toroidal crystals with Ge 311 reflection set to provide EXAFS at the Cu K-edge (energy range 8.9-9.8 keV) and Ge 400 reflection set to provide EXAFS at the Ta L3-edge (9.8-10.7 keV). Key performance characteristics of the spectrometer were found to be consistent with design parameters. The data generated at the National Ignition Facility have shown an ≃3 eV spectral resolution for the Cu K-edge configuration and ≃6 eV for the Ta L3-edge configuration.

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.

This paper describes a new class of focusing crystal forms for the x-ray Bragg crystal spectroscopy of small, point-like, x-ray sources. These new crystal forms are designed with the aid of sinusoidal spirals, a family of curves, whose shapes are defined by only one parameter, which can assume any real value. The potential of the sinusoidal spirals for the design x-ray crystal spectrometers is demonstrated with the design of a toroidally bent crystal of varying major and minor radii for measurements of the extended x-ray absorption fine structure near the Ta-L3 absorption edge at the National Ignition Facility.

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., T e , n Z , and ΔZ eff ). 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.

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.

Objective: Serious pediatric illness places great stress on families. Parents who learn coping skills may better manage these stressors. This study sought to develop and refine a stress coping intervention for parents of hospitalized children, assess the intervention acceptability among these parents, and gather preliminary data on stress, negative and positive affect, anxiety, depression, and self-efficacy., Methods: We conducted an observational study in 2 phases, enrolling parents of children who were inpatients with serious illness, 10 in Phase 1 and 40 in Phase 2. All parents completed at baseline measures of stress and psychological well-being and were introduced to the Coping Kit for Parents. Follow-up interviews were conducted at 1 week (all parents) and 1 month (Phase 2 parents only) regarding the acceptability of the intervention., Results: At baseline, parents reported that stressful situations were frequent (mean = 30.6, standard deviation [SD] = 6.8) and difficult (mean = 26.2, SD = 7.1) and revealed elevated levels of negative affect (mean = 27.3, SD = 7.7), depression (mean = 8.5, SD = 3.7), and anxiety (mean = 11.3, SD = 3.1) and moderate levels of self-efficacy related to their child's illness (mean = 3.3, SD = 0.5). The majority of parents used the kit regularly and on a scale of 1 to 7 agreed that the kit was helpful (mean = 6.0, SD = 0.9), interesting (mean = 5.7, SD = 1.3), practical (mean = 5.7, SD = 1.4), enjoyable (mean = 6.0, SD = 1.3), and they would recommend it to other parents (mean = 6.4, SD = 0.9)., Conclusions: The Coping Kit for Parents is an acceptable stress management intervention that could be made available to parents of children with serious illness at pediatric hospitals with minimal staff training or time commitment., (Copyright © 2018 Academic Pediatric Association. Published by Elsevier Inc. All rights reserved.)

The here-described spectrometer was developed for the extended x-ray absorption fine structure spectroscopy of high-density plasmas at the National Ignition Facility. It employs as the Bragg reflecting element a new type of toroidally bent crystal with a constant and very large major radius R and a much smaller, locally varying, minor radius r. The focusing properties of this crystal and the experimental arrangement of the source and detector make it possible to (a) fulfill the conditions for a perfect imaging of an ideal point source for each wavelength, (b) obtain a high photon throughput, (c) obtain a high spectral resolution by eliminating the effects of source-size broadening, and (d) obtain a one-dimensional spatial resolution with a high magnification perpendicular to the main dispersion plane.

A high resolution, Diagnostic Instrument Manipulator (DIM)-based x-ray Bragg crystal spectrometer has been calibrated for and deployed at the National Ignition Facility (NIF) to diagnose plasma conditions in ignition capsules near stagnation times. The spectrometer has two conical crystals in the Hall geometry focusing rays from the Kr He α , Ly α , and He β complexes onto a streak camera, with the physics objectives of measuring time-resolved electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. A third von Hámos crystal that time-integrates the Kr He α , He β and intervening energy range provides in situ calibration for the streak camera signals. The spectrometer has been absolutely calibrated using a microfocus x-ray source, an array of CCD and single-photon-counting detectors, and multiple K- and L-absorption edge filters at the Princeton Plasma Physics Laboratory (PPPL) x-ray laboratory. Measurements of the integrated reflectivity, energy range, and energy resolution for each crystal are discussed. These calibration data provide absolute x-ray signal levels for NIF measurements, enabling precise filter selection and comparisons to simulations.

Newly developed large-area pixelated two-dimensional detector and two-crystal assemblies were deployed for the first time on tokamaks to enable time-resolved Bragg-diffracted x-ray imaging with good framing rate and water-cooling capabilities for in-vacuum long-pulse operations. High-quality helium-like (He-like) and hydrogen-like (H-like) argon spectra have been observed simultaneously for the first time on a single detector for a wide range of plasma parameters to infer both ion temperature and rotation profiles and support studies on spontaneous rotation, impurity transport, and RF physics. Since tokamak plasmas rotate in both the poloidal (θ) and toroidal (ϕ) directions, a reliable wavelength calibration is needed to account for the correct Doppler shift as well as to compute the spectrometer's instrumental function. Ly α lines emitted from Cd x-ray tubes are proposed to be used as "markers" to provide an in situ calibration of the EAST's X-ray imaging crystal spectrometer systems measuring He- and H-like argon spectra. The first lab test indicated that the X-ray tube can excite strong Ly α lines at 15 kV voltage and 1 mA current when the crystal is shined for 10 min. Other indirect calibration methods using locked-mode discharge scenarios were also studied as complementary methods.

A two-crystal X-ray spectrometer system has been implemented in the EAST tokamak to simultaneously diagnose high- and low-temperature plasmas using He- and H-like argon spectra. But for future fusion devices like ITER and Chinese Fusion Engineering Test Reactor (CFETR), argon ions become fully stripped in the core and the intensity of the H-like lines will be significantly at high temperatures (T e > 5 keV). With increasing auxiliary heating power on EAST, the core plasma temperature could also reach 5 keV and higher. In such conditions, the use of a xenon puff becomes an appropriate choice for both ion-temperature and flow-velocity measurements. A new two-crystal system using a quartz 110 crystal (2d = 4.913 Å) to view He-like argon lines and a quartz 011 crystal (2d = 6.686 Å) to view Ne-like xenon spectra has been deployed on a poloidal X-ray crystal spectrometer. While the He-like argon spectra will be used to measure the plasma temperature in the edge plasma region, the Ne-like xenon spectra will be used for measurement in the hot core. The new crystal arrangement allows a wide temperature measurement ranging from 0.5 to 10 keV or even higher, being the first tests for burning plasmas like ITER and CFETR. The preliminary result of lab-tests, Ne-like xenon lines measurement will be presented.

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.

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, n e 2 Z eff 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.