Line Brightnesses Research Articles

Realization of a gas puff imaging system on the Wendelstein 7-X stellarator.

A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the "Gas-Puff Imaging" (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system's plasma-facing components. The system features a pair of "converging-diverging" nozzles for partially collimating the gas puffed locally ≈135mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera. The DEGAS 2 neutral code was used to simulate the Hα (656nm) and HeI (587nm) line emission expected from well-characterized gas-puffs of H2 and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal-to-noise ratios (>100 at 2 Mframes/s) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the two-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge and scrape-off layer and in and around the magnetic islands outside the LCFS that make up the island divertor configuration employed on W7-X.

The Solar Minimum Eclipse of 2019 July 2. II. The First Absolute Brightness Measurements and MHD Model Predictions of Fe x, xi, and xiv out to 3.4 R ⊙

We present the spatially resolved absolute brightness of the Fe x, Fe xi, and Fe xiv visible coronal emission lines from 1.08 to 3.4 R ⊙, observed during the 2019 July 2 total solar eclipse (TSE). The morphology of the corona was typical of solar minimum, with a dipole field dominance showcased by large polar coronal holes and a broad equatorial streamer belt. The Fe xi line is found to be the brightest, followed by Fe x and Fe xiv (in disk B ⊙ units). All lines had brightness variations between streamers and coronal holes, where Fe xiv exhibited the largest variation. However, Fe x remained surprisingly uniform with latitude. The Fe line brightnesses are used to infer the relative ionic abundances and line-of-sight-averaged electron temperature (T e ) throughout the corona, yielding values from 1.25 to 1.4 MK in coronal holes and up to 1.65 MK in the core of streamers. The line brightnesses and inferred T e values are then quantitatively compared to the Predictive Science Inc. magnetohydrodynamic model prediction for this TSE. The MHD model predicted the Fe lines rather well in general, while the forward-modeled line ratios slightly underestimated the observationally inferred T e within 5%–10% averaged over the entire corona. Larger discrepancies in the polar coronal holes may point to insufficient heating and/or other limitations in the approach. These comparisons highlight the importance of TSE observations for constraining models of the corona and solar wind formation.

Multi-instrument analysis of far-ultraviolet aurora in the southern hemisphere of comet 67P/Churyumov-Gerasimenko

Aims.We aim to determine whether dissociative excitation of cometary neutrals by electron impact is the major source of far-ultraviolet (FUV) emissions at comet 67P/Churyumov-Gerasimenko in the southern hemisphere at large heliocentric distances, both during quiet conditions and impacts of corotating interaction regions observed in the summer of 2016.Methods.We combined multiple datasets from the Rosetta mission through a multi-instrument analysis to complete the first forward modelling of FUV emissions in the southern hemisphere of comet 67P and compared modelled brightnesses to observations with the Alice FUV imaging spectrograph. We modelled the brightness of OI1356, OI1304, Lyman-β, CI1657, and CII1335 emissions, which are associated with the dissociation products of the four major neutral species in the coma: CO2, H2O, CO, and O2. The suprathermal electron population was probed by the Ion and Electron Sensor of the Rosetta Plasma Consortium and the neutral column density was constrained by several instruments: the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), the Microwave Instrument for the Rosetta Orbiter and the Visual InfraRed Thermal Imaging Spectrometer.Results.The modelled and observed brightnesses of the FUV emission lines agree closely when viewing nadir and dissociative excitation by electron impact is shown to be the dominant source of emissions away from perihelion. The CII1335 emissions are shown to be consistent with the volume mixing ratio of CO derived from ROSINA. When viewing the limb during the impacts of corotating interaction regions, the model reproduces brightnesses of OI1356 and CI1657 well, but resonance scattering in the extended coma may contribute significantly to the observed Lyman-βand OI1304 emissions. The correlation between variations in the suprathermal electron flux and the observed FUV line brightnesses when viewing the comet’s limb suggests electrons are accelerated on large scales and that they originate in the solar wind. This means that the FUV emissions are auroral in nature.

ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz

Context.Low and intermediate mass stars are known to power strong stellar winds when evolving through the asymptotic giant branch (AGB) phase. Initial mass, luminosity, temperature, and composition determine the pulsation characteristics of the star and the dust species formed in the pulsating photospheric layers. Radiation pressure on these grains triggers the onset of a stellar wind. However, as of today, we still cannot predict the wind mass-loss rates and wind velocities from first principles neither do we know which species are the first to condense in the upper atmospheric regions.Aims.We aim to characterise the dominant physical, dynamical, and chemical processes in the inner wind region of two archetypical oxygen-rich (C/O < 1) AGB stars, that is, the low mass-loss rate AGB star R Dor (Ṁ~ 1 × 10−7M⊙yr−1) and the high mass-loss rate AGB star IK Tau (Ṁ~ 5 × 10−6M⊙yr−1). The purpose of this study is to observe the key molecular species contributing to the formation of dust grains and to cross-link the observed line brightnesses of several species to the global and local properties of the star and its wind.Methods.A spectral line and imaging survey of IK Tau and R Dor was made with ALMA between 335 and 362 GHz (band 7) at a spatial resolution of ~150 mas, which corresponds to the locus of the main dust formation region of both targets.Results.Some two hundred spectral features from 15 molecules (and their isotopologues) were observed, including rotational lines in both the ground and vibrationally excited states (up tov= 5 for SiO). Detected species include the gaseous precursors of dust grains such as SiO, AlO, AlOH, TiO, and TiO2. We present a spectral atlas for both stars and the parameters of all detected spectral features. A clear dichotomy for the sulphur chemistry is seen: while CS, SiS, SO, and SO2are abundantly present in IK Tau, only SO and SO2are detected in R Dor. Also other species such as NaCl, NS, AlO, and AlOH display a completely different behaviour. From some selected species, the minor isotopologues can be used to assess the isotopic ratios. The channel maps of many species prove that both large and small-scale inhomogeneities persist in the inner wind of both stars in the form of blobs, arcs, and/or a disk. The high sensitivity of ALMA allows us to spot the impact of these correlated density structures in the spectral line profiles. The spectral lines often display a half width at zero intensity much larger than expected from the terminal velocity,v∞, previously derived for both objects (36 km s−1versusv∞~ 17.7 km s−1for IK Tau and 23 km s−1versusv∞~ 5.5 km s−1for R Dor). Both a more complex 3D morphology and a more forceful wind acceleration of the (underlying) isotropic wind can explain this trend. The formation of fractal grains in the region beyond ~400 mas can potentially account for the latter scenario. From the continuum map, we deduce a dust mass of ~3.7 × 10−7M⊙and ~2 × 10−8M⊙for IK Tau and R Dor, respectively.Conclusions.The observations presented here provide important constraints on the properties of these two oxygen-dominated AGB stellar winds. In particular, the ALMA data prove that both the dynamical and chemical properties are vastly different for this high mass-loss rate (IK Tau) and low mass-loss rate (R Dor) star.

THE DETECTABILITY OF MILLIMETER-WAVE MOLECULAR ROTATIONAL TRANSITIONS

ABSTRACT Elaborating on a formalism that was first expressed some 40 years ago, we consider the brightness of low-lying millimeter-wave rotational lines of strongly polar molecules at the threshold of detectability. We derive a simple expression relating the brightness to the line-of-sight integral of the product of the total gas and molecular number densities and a suitably defined temperature-dependent excitation rate into the upper level of the transition. Detectability of a line is contingent only on the ability of a molecule to channel enough of the ambient thermal energy into the line, and the excitation can be computed in bulk by summing over rates without solving the multi-level rate equations, or computing optical depths and excitation temperatures. Results for , HNC, and CS are compared with escape-probability solutions of the rate equations using closed-form expressions for the expected range of validity of our ansatz, with the result that gas number densities as high as or optical depths as high as 100 can be accommodated in some cases. For densities below a well-defined upper bound, the range of validity of the discussion can be cast as an upper bound on the line brightness which is 0.3 K for the J = 1–0 lines and 0.8–1.7 K for the J = 2–1 lines of these species. The discussion casts new light on the interpretation of line brightnesses under conditions of weak excitation, simplifies derivation of physical parameters, and eliminates the need to construct grids of numerical solutions of the rate equations.

OBSERVATION AND MODELING OF GEOCORONAL CHARGE EXCHANGE X-RAY EMISSION DURING SOLAR WIND GUSTS

Solar wind charge exchange (SWCX) X-rays are emitted when highly charged solar wind ions such as O{sup 7{sup +}} collide with neutral gas, including the Earth's tenuous outer atmosphere (exosphere or geocorona) and hydrogen and helium from the local interstellar medium drifting through the heliosphere. This geocoronal and heliospheric emission comprises a significant and varying fraction of the soft X-ray background (SXRB) and is seen in every X-ray observation, with the intensity dependent on solar wind conditions and observation geometry. Under the right conditions, geocoronal emission can increase the apparent SXRB by roughly an order of magnitude for an hour or more. In this work, we study a dozen occasions when the near-Earth solar wind flux was exceptionally high. These gusts of wind lead to abrupt changes in SWCX X-ray emission around Earth, which may or may not be seen by X-ray observatories depending on their line of sight. Using detailed three-dimensional magnetohydrodynamical simulations of the solar wind's interaction with the Earth's magnetosphere, and element abundances and ionization states measured by ACE, we model the time-dependent brightness of major geocoronal SWCX emission lines during those gusts and compare with changes in the X-ray background measured by the Chandra X-ray Observatory.more » We find reasonably good agreement between model and observation, with measured geocoronal line brightnesses averaged over 1 hr of up to 136 photons s{sup –1} cm{sup –2} sr{sup –1} in the O VII Kα triplet around 564 eV.« less

Impurity production monitoring during RF experiments in Tore Supra

Real time monitoring of edge plasma impurity content is used in a radiofrequency heated plasma scenario, to operate the tokamak safely by preventing any large increase in the impurity source, and to asses the global machine conditions after wall conditioning procedures. By means of high resolution Vacuum Ultraviolet spectroscopy, the main intrinsic impurity line brightnesses (C IV, O IV, Fe XV and Cu XIX) are routinely monitored and stored in a database along with basic plasma parameters (plasma current, electron density, injected power). The radiated power and the effective charge are also included for data consistency analysis. This paper describes the impurity monitoring technique implemented on Tore Supra (TS) and presents the main results concerning the evolution of the plasma edge impurity content for two scenarios performed on TS: high power scenario and long pulse duration scenario.

UV and optical emission lines from the z 2.6 radio galaxy 0828+193: spatially resolved measurements

We present an investigation into the spatial variation of the rest-frame UV and optical line and continuum emission along the radio axis of the z=2.6 radio galaxy 0828+193, using long-slit spectra from the Keck II and Subaru telescopes. Line brightnesses, line ratios and electron temperatures are examined, and their relationship with the arm-length asymmetry of the radio source is also investigated. We find that on the side of the nucleus with the shortest radio lobe, the gas covering factor is higher, and the ionization parameter is lower. The contrasts in environmental density required to explain the asymmetries in the line brightness and the radio arm-length asymmetries are in fair agreement with each other. These results add further weight to the conclusion of McCarthy, van Breugel & Kapahi (1991) - lobe distance asymmetries in powerful radio sources are the result of an asymmetry in the environmental density. We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric.

Formation, fractionation, and excitation of carbon monoxide in diffuse clouds

Aims: Our aims are threefold: a) To compare the $uv$ and mm-wave results; b) to interpret 13CO and 12CO abundances in terms of the physical processes which separately and jointly determine them; c) to interpret observed J=1-0 rotational excitation and line brightness in terms of ambient gas properties. Methods: A simple phenomenological model of CO formation as the immediate descendant of quiescently-recombining HCO+ is used to study the accumulation, fractionation and rotational excitation of CO in more explicit and detailed models of H2-bearing diffuse/H I clouds Results: The variation of N(CO) with N(H2) is explained by quiescent recombination of a steady fraction n(HCO+)/n(H2) = 2 x 10^{-9}. Observed N(12CO))/N(13CO) ratios generally do not require a special chemistry but result from competing processes and do not provide much insight into the local gas properties, especially the temperature. J=1-0 CO line brightnesses directly represent N(CO), not N(H2), so the CO-H2 conversion factor varies widely; it attains typical values at N(12CO) \la 10^{16}cm^{-2}. Models of CO rotational excitation account for the line brightnesses and CO-H2 conversion factors but readily reproduce the observed excitation temperatures and optical depths of the rotational transitions only if excitation by H-atoms is weak -- as seems to be the case for the very most recent calculations of these excitation rates.

Cyclic variation in the spatial distribution of the coronal green line brightness

The spatial and temporal brightness distributions of the Fe XIV 530.3 nm coronal green line (CGL) and cyclic variations of these distributions are analyzed for a long time interval covering more than five 11-year cycles (1943–2001). The database of line brightnesses is visually represented in the form of a movie. Substantial restructuring of the spatial distribution of the CGL brightness occur over fairly short time intervals near the so-called reference points of the solar cycle; such points can be identified based on various sets of solar-activity indices. Active longitudes are observed in the CGL brightness over 1.5–3 yr. Antipodal and “alternating” active longitudes are also detected. The movie can be used to compare the CGL brightness data with other indicators of solar activity, such as magnetic fields. The movie is available at http://helios.izmiran.rssi.ru/hellab/Badalyan/green/.

Experimental and simulated M-shell nickel spectra in the 14.4–18.0 nm region frommagnetic fusion devices

Experimental M-shell nickel spectra in the 14.4–16.5 nm region from the JET tokamak(from both divertor and limiter configurations) and from the reversed field pinch RFX havebeen simulated. These spectra include lines from five ionization states, namely from K-likeNi9+ to P-likeNi13+ ions.For the JET limiter configuration the spectrum upper wavelength limit was higher (18.0 nm) and lines fromSi-like Ni14+ ions were also observed. Collisional–radiative (CR) models have been built forthese six Ni ions, considering electron collisional excitation and radiative decayas the main populating processes for the excited states. These models givephoton emission coefficients (PECs) for the emitted lines at electron density(ne) andtemperature (Te) values corresponding to the experimental situations. Impurity modelling is performed using a1D impurity transport code, calculating the steady state radial distribution of the Ni ions. TheNi line brightnesses are evaluated in a post-processing subroutine and simulated spectra areobtained. The spectrum from a single ion, in the absence of blendings, depends only on theTe and ne values in the emitting shell of the ionization state considered. On the other hand, thesuperposition of these spectra depends on the experimental conditions, as a consequence ofthe fact that the ion charge distribution depends not only on the radial profiles ofTe and ne, but also on the chosen ionization and recombination rate coefficients and on the radialprofiles of the impurity transport coefficients in the region of the emitting shells. Since theaim of the paper is the investigation of the atomic physics of the M-shell ions, the sectiondiscussing the plasma physics phenomena is purposely limited. For each experimentalspectrum a few simulations are presented, since a unique choice has not beenfound by selecting the input parameters of the transport code. The effect of theTe and ne values on the emitting shells as well as the influence of line blendings on the single-ionization-degreespectra are stressed. These, in turn, are then compared with the predictions. For thene range considered the PECs are practically independent ofne.The Te dependence is much reduced due to the fact that the spectral fits performed are actuallycomparisons of line ratios. The agreement found between experimental and simulatedsingle-ionization-degree spectra gives confidence in the atomic data used in the CR models.

Experimental and simulated VUV spectra from the JET tokamak and thereversed field pinch RFX

Experimental VUV spectra from the JET tokamak and from the reversed field pinch RFX have been simulated. For the former device both n = 2 to n = 2 L-shell Ar and Ne spectra (respectively, in the 14.5-43.0 and in the 35.0-80.0 nm ranges) were considered, whereas for RFX only the Ne spectrum was available. The spectra have been observed with the SPRED spectrometer. From the simulation of the spectra, relative sensitivity curves have been obtained for each instrument in the ranges of the simulation. For RFX only, it has been possible to extend this curve from ~13.0 to ~105 nm, by simulating intrinsic C and O emissions. The photon emission coefficients of the lines with wavelengths in the ranges of the experimental spectra were obtained from collisional-radiative models. For Ar and Ne these coefficients have been calculated by the Hebrew University Lawrence Livermore Atomic Codes atomic physics codes, whereas for C and O the corresponding coefficients have been taken from the `Atomic Data and Analysis Structure' database. Impurity modelling is performed using a one-dimensional impurity transport code, calculating for each atomic species the radial distribution of the impurity ions. The line brightnesses are evaluated in a post-processing subroutine and the simulations of the spectra are obtained. The spectral simulations (including impurity ion transport) give confidence in the atomic physics calculations, and allow the determination of the transport coefficients in the plasma regions from which the considered ionization states emit. Finally, the obtained relative sensitivity curves of the two SPRED spectrometers have been compared with the calibrations performed by means of the branching ratio technique.

Experimental and simulated neon spectra in the 10-nm wavelength region from tokamak and reversed field pinch plasmas

Experimental neon spectra (in the 10-nm region), from the tokamak Tore Supra and the reversed field pinch experiment RFX, have been simulated. The spectra include lines from three neon ionization states, namely Ne(7+), Ne(6+), and Ne(5+) ions. Collisional radiative models have been built for these three Ne ions, considering electron collisional excitation and radiative decay as populating processes of the excited states. These models give photon emission coefficients for the emitted lines at electron density and temperature values corresponding to the experimental situations. Impurity modelling is performed using a one-dimensional impurity transport code, calculating the steady-state radial distribution of the Ne ions. The Ne line brightnesses are evaluated in a post-process subroutine and simulated spectra are obtained. The parts of the spectra corresponding to a single ionization state do not depend on the experimental conditions and show good agreement with the simulated single ionization state spectra. On the other hand, the superposition of the three spectra depends on the experimental conditions, as a consequence of the fact that the ion charge distribution depends not only on the radial profiles of the electron density and temperature, but also of the impurity transport coefficients. Simulations of the Ne spectra (including transport) give confidence in the atomic physics calculations; moreover, they allow the determination of the transport coefficients in the plasma region emitting the considered ionization states.

Collisional-Radiative models for hydrogen-like and helium-like carbon and oxygen ions and applications to experimental data from the TS tokamak and the reversed field pinch RFX

Collisional radiative models (CRM) are needed to simulate experimental line brightnesses and emissivities from fusion devices. CRM are built for H-like and He-like carbon and oxygen ions, following a detailed review of the published literature on the required atomic data (including both collision rate coefficients and atomic transition probabilities). The impurity ion radial distribution is obtained using a transport code with two radius dependent transport parameters: a diffusion coefficient D and an inward convection velocity V. Reliable atomic data are a prerequisite to these simulations, since they are supposed to be well known; adjustement of the simulations to the experimental line and/or continuum brightnesses and emissivities is done by varying only D and V. Examples are given of the quantitative interpretation of experimental spectroscopic data from two fusion devices: the Tore Supra Tokamak and the Reversed Field Pinch RFX. As a consequence of the order of magnitude difference in the central electron temperatures in the two devices, the sensitivity of the H-like and He-like ion emissions to the transport parameters is different. These differences are highlighted in the examples given.

Impurity transport in Alcator C-Mod plasmas

Trace non-recycling impurities have been injected into Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] plasmas in order to determine impurity transport coefficients. Subsequent impurity emission has been observed with spatially scanning x-ray and Vacuum Ultra-Violet (VUV) spectrometer systems. Measured time-resolved brightness profiles of helium- and lithium-like transitions have been compared with those calculated from a transport code which includes impurity diffusion and convection in conjunction with an atomic physics package for individual line emission. During Low-Confinement-Mode (L-mode) plasmas, the transport can be characterized by pure diffusion, with coefficients ∼5000 cm2/s, reflecting the ∼20 ms decay in the x-ray and VUV line brightnesses. During High-Confinement-Modes (H-modes), the impurity confinement times are much longer, and the modelling requires that there be a strong inward convection (of order 1000 cm/s) near the plasma edge, with greatly reduced diffusion (of order 100 cm2/s), also in the region of the edge transport barrier. These edge values of the transport coefficients during H-mode are qualitatively similar to the neo-classical values. Nitrogen has also been injected, and after the H- to L-mode transition, the inner shell satellite lines of lithium-like nitrogen dominate in intensity the resonance line of helium-like N5+ in a thin shell near the plasma edge.

How to beat the low resolution of multilayer mirror spectra (invited)

The soft x-ray and extreme ultraviolet (XUV) impurity emissions from tokamaks (10 Å<λ<304 Å) have been extensively studied with high-resolution grazing incidence spectrographs, and atomic physics models predicting spectral line brightnesses have been benchmarked against these experimental data. This, together with the ability to perform large amounts of accurate atomic physics computations, enables the relaxation on the requirement for high resolution spectra. The multilayer mirror (MLM) is a low resolving power (λ/δ λ<100) XUV dispersive/reflective optical element that obeys the Bragg law of reflection. MLM based monitors are compact, high-photon-throughput diagnostics capable of extracting XUV emissions of impurities from the harsh environment of large fusion reactor-type devices. We will show how atomic physics modeling can be used to extract the XUV spectral line brightnesses measured with low-resolution, high-photon-throughput, MLM-based devices. The Plasma Spectroscopy Group at The Johns Hopkins University has investigated the application of MLM based diagnostics for magnetically confined fusion plasmas: MLM based monitors have been constructed for and extensively used on DIII–D, Alcator C-Mod, TEXT, Phaedrus-T, and CDX-U to study the impurity behavior of elements ranging from He to Mo. Experiments were also performed in which MLMs were irradiated to a fast neutron fluence of 1.1×1019 n cm−2 at 270–300 °C, and the preliminary results indicate that MLMs would be a good first wall reflector for fusion plasmas. Future applications of MLM based devices to study divertor coolants (Ne, Ar, and Kr emissions) and “killer pellet” (W emissions) experiments will also be discussed.

Observation of O V visible transitions in a tokamak divertor plasma.

We report the observation of two unusually bright, visible lines from Be I--like oxygen, an impurity intrinsic to tokamak plasmas. Collisional-radiative (CR) models using detailed atomic structure are used to predict line brightnesses in agreement with observations. Because the O V ion exists in the divertor region of a tokamak, and since visible transitions can be easily measured, these lines can serve as a useful diagnostic of impurity concentration and ion temperature in a region of the plasma crucial to impurity control and energy balance.

Detection of O II 2471-A forbidden line from the Io plasma torus

view Abstract Citations (21) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of [O ii] lambda 2471 from the Io Plasma Torus McGrath, M. A. ; Feldman, P. D. ; Strobel, D. F. ; Moos, H. W. ; Ballester, G. E. Abstract We report the first detection of the O II 2471-A forbidden line from the Io plasma torus. Observations of the east and west torus ansae at 5.7 R(J) on 1992 March 15 and May 1, respectively, using the Goddard High Resolution Spectrograph of the HST have resulted in about 5-sigma detections of the line on both occasions, with line brightnesses of 30 +/- 5 R and 28 +/- 5 R for the east and west ansae respectively in a 2 x 2 arcsec FOV. The lines are Doppler-shifted relative to the rest wavelength (vacuum) of 2471.04 A, with a separation of 1.30 +/- 0.25 A between the east and west lines, implying a torus rotation velocity of 79 +/- 15 km/s, consistent with that expected at a radial distance of 5.7 R(J). Assuming a torus electron temperature and density distribution consistent with Voyager I in situ measurements and homogeneous mixing of O(+) relative to electron density along the line of sight, the observed line brightnesses imply an average O(+) mixing ratio of 0.26 +/- 0.05, in agreement with a value derived previously by Moos et al. (1991), but lower than that derived from Voyager observations. There is no significant difference in average brightness between the east (dawn) and west (dusk) ansa observations. Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/187031 Bibcode: 1993ApJ...415L..55M Keywords: Io; Jupiter Atmosphere; Oxygen Spectra; Planetary Magnetospheres; Satellite Atmospheres; Toroidal Plasmas; Solar System; Ultraviolet Spectrometers; Lunar and Planetary Exploration; PLANETS AND SATELLITES: INDIVIDUAL JUPITER; PLANETS AND SATELLITES: INDIVIDUAL IO; PLASMAS; ULTRAVIOLET: SOLAR SYSTEM full text sources ADS | data products MAST (2) ESA (1)

Iron concentration measurements on TFTR using charge exchange excited lines of helium-like iron in the 200–700 Å region

Charge exchange excited lines of Fe23+ in the EUV region have been observed on the TFTR tokamak. These lines are emitted by Δn=1 transitions between levels with n=6–10 following charge exchange recombination of He-like iron ions (Fe24+) with deuterium atoms injected by neutral beams. Iron concentrations are obtained by modeling the line brightnesses using a beam attenuation code and iron charge exchange cross sections. The results are in good agreement with iron concentrations obtained from impurity transport code modeling of the brightnesses of EUV electron impact excited lines, demonstrating that charge exchange excited lines may be reliably used to measure local metallic impurity concentrations.