Multichannel grazing-incidence spectrometer for plasma impurity diagnosis: SPRED
TL;DR: A compact vacuum ultraviolet spectrometer system has been developed to provide time-resolved impurity spectra from tokamak plasmas and its sensitivity is comparable with that of a conventional grazing-incidence monochromator.
Abstract: A compact vacuum ultraviolet spectrometer system has been developed to provide time-resolved impurity spectra from tokamak plasmas. Two interchangeable aberration-corrected toroidal diffraction gratings with flat focal fields provide simultaneous coverage over the ranges 100–1100 A or 160–1700 A. The detector is an intensified self-scanning photodiode array. Spectral resolution is 2 A with the higher dispersion grating. Minimum readout time for a full spectrum is 20 msec, but up to seven individual spectral lines can be measured with a 1-msec time resolution. The sensitivity of the system is comparable with that of a conventional grazing-incidence monochromator.
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281 citations
TL;DR: In this paper, the spectral features of W at 0.4?0.8?nm, around 5?nm and around 12 and 14?nm have been recorded and compared with modelling results.
Abstract: Tungsten (W) has moved into the focus of fusion research being a main candidate for the plasma facing components (PFCs) of ITER and a future fusion reactor. A main ingredient for understanding the influence of W as a plasma impurity and its impact on the plasma is the spatially resolved spectroscopic diagnosis of W. The focus of the experimental investigations at ASDEX Upgrade is on the most intense emissions of W ions (about I-like W21+ to Mn-like W49+) in the VUV to the soft x-ray region covering the electron temperature range from about 0.5?5.0?keV. The relative shape of the fractional abundances of the ionization stages Se-like W40+ to Ni-like W46+ and of the bundle of ionization stages between Sn-like W24+ and Y-like W35+ was determined. Calculated fractional abundances using published ionization and recombination rates do not accurately describe the experimental temperature dependence. Adjustments to the recombination rates were calculated to reconcile with the measurements. The spectral features of W at 0.4?0.8?nm, around 5?nm, between 12 and 14?nm and between 10 and 30?nm have been recorded and compared with modelling results. The quality of agreement is best for highly charged ionization stages and short wavelengths and decreases for lower charged ionization stages and longer wavelengths. However, in the latter case the predictions manage to reproduce the total emissivity in each considered spectral range and also the rough distribution of emissions versus wavelengths within these spectral ranges. The modelling of the SXR range at 0.4?0.8?nm looks very similar to the measurement. Further observations of weaker spectral features between 0.6 and 0.7?nm, between 1.8 and 3.5?nm and at 8?nm could be attributed to certain ionization stages. The modelling of W spectra for ITER predicts emissions of Cr-like W50+ to about C-like W68+ at 0.1?0.15?nm, 1.8?4.0?nm and around 8?nm.
264 citations
TL;DR: A high-resolution, time-resolving soft x-ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics as discussed by the authors.
Abstract: A high‐resolution, time‐resolving soft x‐ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics. The basic instrument is a high‐resolution, interferometrically adjusted, extreme grazing incidence Schwob–Fraenkel duochromator. The instrument is equipped with two multichannel detectors that are adjusted interferometrically and scan along the Rowland circle. Each consists of an MgF2 coated, funneled microchannel plate, associated with a phosphor screen image intensifier that is coupled to a 1024‐element photodiode array by a flexible fiber‐optic conduit. The total wavelength coverage of the instrument is 5–340 A with a measured resolution (FWHM) of about 0.2 A when equipped with a 600‐g/mm grating, and 5–85 A with a resolution of about 0.06 A using a 2400‐g/mm grating. The simultaneous spectral coverage of each detector varies from 15 A at the short wavelength limit to 70 A at the long wavelength limit with the lower dispersion grating. The minimum readout time for a full spectral portion is 16 ms, but several individual lines can be measured with 1‐ms time resolution by selected pixel readout. Higher time resolution can be achieved by replacing one multichannel detector with a single channel electron multiplier detector. Examples of data from the PLT and TFTR tokamaks are presented to illustrate the instrument’s versatility, high spectral resolution, and high signal‐to‐noise ratio even in the 10‐A region.
165 citations
TL;DR: In this article, a transport code (TRANSP) is used to simulate future deuterium-tritium (DT) experiments in TFTR DD discharges, and the modelling of one supershot is discussed in detail to indicate the degree of accuracy of the TRANSP modelling.
Abstract: A transport code (TRANSP) is used to simulate future deuterium-tritium (DT) experiments in TFTR. The simulations are derived from 14 TFTR DD discharges, and the modelling of one supershot is discussed in detail to indicate the degree of accuracy of the TRANSP modelling. Fusion energy yields and alpha particle parameters are calculated, including profiles of the alpha slowing down time, the alpha average energy, and the Alfven speed and frequency. Two types of simulation are discussed. The main emphasis is on the DT equivalent, where an equal mix of D and T is substituted for the D in the initial target plasma, and for the D0 in the neutral beam injection, but the other measured beam and plasma parameters are unchanged. This simulation does not assume that alpha heating will enhance the plasma parameters or that confinement will increase with the addition of tritium. The maximum relative fusion yield calculated for these simulations is QDT ~ 0.3, and the maximum alpha contribution to the central toroidal β is βα(0) ~ 0.5%. The stability of toroidicity induced Alfven eigenmodes (TAE) and kinetic ballooning modes (KBM) is discussed. The TAE mode is predicted to become unstable for some of the simulations, particularly after the termination of neutral beam injection. In the second type of simulation, empirical supershot scaling relations are used to project the performance at the maximum expected beam power. The MHD stability of the simulations is discussed
160 citations
TL;DR: A new type of grazing-incidence spectrometer with a flat focal field is developed, and XUV spectroscopy in the extreme ultraviolet region ranging from 15 to 200 A is carried out, showing the importance of the transient treatment of picosecond laser-produced plasmas.
Abstract: A new type of grazing-incidence spectrometer with a flat focal field is developed, and XUV spectroscopy in the extreme ultraviolet region ranging from 15 to 200 A is carried out. Soft x-ray line spectra emitted from picosecond laser plasmas of aluminum and iron targets are measured and good resolutions are obtained in the XUV region. The spectral regions of detection are extended to shorter wavelengths (15 A) using a finer spaced grating. Computational studies on x-ray spectra are also performed taking into account the transient characteristics of picosecond laser-produced plasmas; the importance of the transient treatment is clearly shown. This type of soft x-ray spectrometer should be useful for time-resolved picosecond soft x-ray spectroscopy.
156 citations
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TL;DR: The performance characteristics of a 1024-element self-scanned photodiode array, related to its use as a multichannel spectrometric detector, including spectral and temporal response, blooming, geometric accuracy, noise sources, dynamic range, signal integration and spectral as well as spatial resolution are described.
Abstract: The performance characteristics of a 1024-element self-scanned photodiode array, related to its use as a multichannel spectrometric detector are described. The parameters discussed include, spectral and temporal response, blooming, geometric accuracy, noise sources, dynamic range, signal integration and spectral as well as spatial resolution.
129 citations
TL;DR: In this paper, Doppler shifts of several atomic spectral lines were used to estimate the time evolution and spatial distribution of the rotation from which a momentum confinement time, comparable to the ion energy confinement time was deduced.
Abstract: Toroidal plasma rotation, generated by toroidally unbalanced neutral-beam injection into the Princeton Large Torus, has been measured by Doppler shifts of several atomic spectral lines. These measurements produce the time evolution and spatial distribution of the rotation from which a momentum confinement time, comparable to the ion energy confinement time, is deduced.
103 citations
TL;DR: In this paper, a low-Z impurity transport in tokamaks was simulated with a one-dimensional impure transport model including both neoclassical and anomalous transports.
Abstract: Low-Z impurity transport in tokamaks was simulated with a one-dimensional impurity transport model including both neoclassical and anomalous transports. The neoclassical fluxes are due to collisions between the background plasma and impurity ions as well as to collisions between the various ionization states. The evaluation of the neoclassical fluxes takes into account the different collisionality regimes of the background plasma and the impurity ions. A limiter scrape-off model is used to define the boundary condition for the impurity ions in the plasma periphery. To account for the spectroscopic measurements of power radiated by the lower ionization states, fluxes due to anomalous transport are included. The sensitivities of the results to uncertainties in rate coefficients and plasma parameters in the periphery are investigated. The implications of the transport model for spectroscopic evaluation of impurity concentrations, impurity fluxes, and radiated power from line emission measurements are discussed.
80 citations
TL;DR: Although the dynamic range of the detector array was severely limited by ion-feedback effects in currently available microchannel array plates, the theoretical spatial resolution of 50 microm was achieved with a detection efficiency at wavelengths below 800 A equal to that of a conventional channel electron multiplier.
Abstract: The performance of a one-dimensional photon-counting detector array based on microchannel array plates has been evaluated in the laboratory over the wavelength range from 461 A to 1216 A. The output charge pulses from a set of cascaded microchannel array plates were collected on a proximity-focused anode array consisting of sixty-four linear electrodes 1.3 mm in length and 25 microm in width, set on 50-microm centers. Although the dynamic range of the detector array was severely limited by ion-feedback effects in currently available microchannel array plates, the theoretical spatial resolution of 50 microm was achieved with a detection efficiency at wavelengths below 800 A equal to that of a conventional channel electron multiplier.
68 citations
TL;DR: In this paper, a method for calibrating vacuum-ultraviolet monochromators for measurement of absolute radiation intensities is described, based on calculating the brightness of an optically thin spectral line in the far ultraviolet from a visible line originating from the same upper level.
Abstract: A method for calibrating vacuum-ultraviolet monochromators for measurement of absolute radiation intensities is described. It is based on calculating the brightness of an optically thin spectral line in the far ultraviolet from the brightness of a visible line originating from the same upper level. A grazing incidence monochromator and a Seya–Namioka monochromator were calibrated at a number of wavelengths between 1640 and 231 A, using line pairs of hydrogen and ionized helium. Light sources used to obtain these lines are described. Problems of measurement and sources of error, particularly in the case of hydrogenlike spectra, are discussed.
66 citations