Ar XVII Research Articles

Spatially Resolved Measurements of Temperature and Rotation Velocity from the Tangential Imaging X-ray Crystal Spectrometer on the EAST Tokamak

A new high-resolution tangential imaging X-ray crystal spectrometer (TXCS) is described for implementation on the Experimental Advanced Superconducting Tokamak (EAST) to provide spatially and temporally resolved data on the toroidal plasma rotation velocity and on the ion and the electron temperature. These data are derived from observations of the satellite spectra of heliumlike argon (Ar XVII). The TXCS will provide data for all experimental conditions, which include ohmically heated discharges as well as plasmas with radio-frequency (RF) waves and neutral-beam heating. The latest experimental results show that lower hybrid waves (LHW) induce a co-current change in a toroidal rotation of up to 45 km/s in the L-mode plasma core region. A modification of the toroidal rotation develops on the extended plasma region and a long time scale (≥1 s). The experimental setup and the initial experimental results are presented.

The first experimental results from x-ray imaging crystal spectrometer for KSTAR

The x-ray imaging crystal spectrometer (XICS) for the Korea Superconducting Tokamak Advanced Research has been first applied for the experimental campaign in 2009. The XICS was designed to provide measurements of the profiles of the ion and electron temperatures from the heliumlike argon (Ar XVII) spectra. The basic functions of the XICS are properly working although some satellites lines are not well matched with the expected theoretical values. The initial experimental results from the XICS are briefly described.

Detection of X-ray polarization of Ar Z-pinch plasma

An X-ray polarization spectrometer has been developed for diagnostic applications of X-ray line polarization spectroscopy in Ar Z-pinch plasmas. The diagnosis was based on theoretical modeling of X-ray line polarization-dependent spectra that have been measured simultaneously by a pair of convex crystal analyzers. Surfaces of the crystals were orthogonal with each other in order to diffract the X-ray spectra. The spectrometer was equipped with two pieces of X-ray films that work as the spectral detector. The experimental results have confirmed that there are considerable differences in relative intensities for the Ar XVII resonance line w (1s2p 1P 1–1s 2 1S 0), the Ar XVII intercombination line y (1s2p 3P 1–1s 2 1S 0) and the Li-like satellites with directions perpendicular and parallel to the Z-pinch axis. Linear polarization of the resonance line and the intercombination line has been calculated according to intensity of the spectra. A value of +0.25 was obtained for the polarization of w and a value of +0.14 for the polarization of y.

A SOLAR SPECTROSCOPIC ABSOLUTE ABUNDANCE OF ARGON FROM RESIK

Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at 3.949 Angstroms and 3.733 Angstroms respectively with the RESIK X-ray spectrometer on the CORONAS-F spacecraft, together with temperatures and emission measures from the two channels of GOES, have been analyzed to obtain the abundance of Ar in flare plasmas in the solar corona. The line fluxes per unit emission measure show a temperature dependence like that predicted from theory, and lead to spectroscopically determined values for the absolute Ar abundance, A(Ar) = 6.44 pm 0.07 (Ar XVII) and 6.49 pm 0.16 (Ar XVIII) which are in agreement to within uncertainties. The weighted mean is 6.45 pm 0.06, which is between two recent compilations of the solar Ar abundance and suggest that the photospheric and coronal abundances of Ar are very similar.

Passive Spectroscopy in Visible, VUV, and X-Ray Ranges for LHD Diagnostics

Various types of spectrometers corresponding to different wavelength ranges from X-ray to visible have been developed for the Large Helical Device (LHD). The charge-coupled device is demonstrated to be a suitable solution as a detector for spectral measurements irrespective of the wavelength range. In the ultraviolet (UV)-visible range, an astigmatism-corrected 1.3-m Czerny-Turner-type spectrometer is developed for a simultaneous measurement with 80 lines of sight. Two other UV-visible spectrometers having focal lengths of 0.3 and 0.5 m, respectively, are also prepared for wide wavelength range measurements. An in situ sensitivity calibration is attempted for these spectrometers, for which visible bremsstrahlung from the LHD plasma is utilized. In the vacuum ultraviolet range (30 to 310 nm), a normal incidence spectrometer having a focal length of 3 m is developed for a spatial intensity profile measurement of impurity ions, especially in the plasma boundary region, and for measurements of line broadening of several impurity ions. A number of forbidden emission lines due to magnetic dipole transitions are also identified with this spectrometer. In the extreme ultraviolet range (1 to 50 nm), flat-field spectrometers are developed for measurements of emission lines from high-Z impurities in the plasma core. Two types of gratings, i.e., mechanically ruled and laminar-type holographic, have been tested, and the latter is found to be preferable with respect to the reflectivity and the resolution power. A Johann-type X-ray crystal spectrometer is developed for measurements of the central ion temperature, for which the resonance line of Ar XVII ion (1s2 1S0 – 1s2p 1P1) is mainly used. The central ion temperature is routinely measured with high time resolution.

Energy Levels and Observed Spectral Lines of Ionized Argon, ArII through ArXVIII

The energy levels and observed spectral lines of ionized argon atoms, in all stages of ionization, have been compiled. Sufficient experimental data were found to generate level and line tables for ArII through ArXV. For ArXVI a mix of experimental and theoretical data were used. Because of the superiority of the theoretical data for ArXVII and ArXVIII, theoretical values are compiled for the energy levels and the lines are calculated from them. Experimental g-factors are included for ArII. A value, either experimental, semiempirical, or theoretical, is included for the ionization energy of each ion.

Imaging x-ray crystal spectrometer on EAST

A high-resolution imaging x-ray crystal spectrometer is described for implementation on the EAST tokamak to provide spatially and temporally resolved data on the ion temperature, electron temperature and poloidal plasma rotation. These data are derived from observations of the satellite spectra of helium-like argon, Ar XVII, which is the dominant charge state for electron temperatures in the range from 0.4 to 3.0 keV and which is accessible to EAST. Employing a novel design, which is based on the imaging properties of spherically bent crystals, the spectrometers will provide spectrally and spatially resolved images of the plasma for all experimental conditions, which include ohmically heated discharges as well as plasmas with rf and neutral-beam heating. The experimental setup and initial experimental results are presented.

RESIK Observations of Helium-like Argon X-Ray Line Emission in Solar Flares

The Ar XVII X-ray line group principally due to transitions 1s2–1s2l (l = s, p) near 4 A was observed in numerous flares by the RESIK bent crystal spectrometer aboard CORONAS-F between 2001 and 2003. The three line features include Ar XVII w (resonance line), a blend of x and y (intercombination lines), and z (forbidden line), all of which are blended with Ar XVI dielectronic satellites. The ratio G, equal to [ I(x) + I(y) + I(z) ]/I(w) , varies with electron temperature Te mostly because of unresolved dielectronic satellites. With temperatures estimated from GOES X-ray emission, the observed G ratios agree fairly well with those calculated from CHIANTI and other data. With a two-component emission measure, better agreement is achieved. Some S XV and S XVI lines blend with the Ar lines, the effect of which occurs at temperatures 8 MK, allowing the S/Ar abundance ratio to be determined. This is found to agree with coronal values. A nonthermal contribution is indicated for some spectra in the repeating-pulse flare of 2003 February 6.

ChandraObservation of Cir X‐1 near the Periastron Passage: Evidence for an X‐Ray Jet?

We present the results of a 25 ks long Chandra observation of the peculiar source Cir X-1 near the periastron passage. We report precise X-ray coordinates of the source, which were compatible with the optical and radio counterpart coordinates. We focus on the study of the detected emission features using the High Energy Transmission Grating Spectrometer on board the Chandra satellite. We detect emission lines associated with Mg XII, Si XIII, Si XIV, S XV, S XVI, Ar XVII, Ar XVIII, Ca XIX, Ca XX, Fe XXV, and Fe XXVI, showing an average redshift of 470 km s−1. The most intense emission features can be fitted with two lines; this is more evident for the 6.6 keV emission feature, which shows a double-peaked structure. We propose that the redshifted and blueshifted lines of Mg XII, Si XIV, S XVI, and Fe XXV can be interpreted as emission from a blue and red beam of an X-ray jet, finding that the angle between the line of sight and the jet direction is 92° and the jet velocity is 0.08c.

XMM-Newton observations ofζOrionis (O9.7 Ib): a collisional ionization equilibrium model

We present XMM-Newton observations of the O supergiant Zeta Orionis (O9.7 Ib). The spectra are rich in emission lines over a wide range of ionization stages. The RGS-spectra show for the first time lines of low ion stages such as C VI, N VI, N VII, and O VII. The line profiles are symmetric and rather broad (FWHM approximately 1500 km/s) and show only a slight blue shift. With the XMM-epic spectrometer several high ions are detected in this star for the first time including Ar XVII and S XV. Simultaneous multi-temperature fits and DEM-modeling were applied to the RGS and EPIC spectra to obtain emission measures, elemental abundances and plasma temperatures. The calculations show temperatures in the range of about 0.07-0.6 keV. According to the derived models the intrinsic source X-ray luminosity at a distance of 251 pc Lx=1.37(.03) times 10^{32} ergs/s, in the energy range 0.3-10 keV. In the best multi-temperature model fit, the abundances of C, N, O, and Fe are near their solar values, while the abundances of Ne, Mg, and Si appear somewhat enhanced. The sensitivity of the He-like forbidden and intercombination lines to Zeta Ori's strong radiation field is used to derive the radial distances at which lines are formed. Values of 34 R-star for N VI, 12.5 R-star for O VII, 4.8 R-star for Ne IX, and 3.9 R-star for Mg XI are obtained.

He-like Ar xvii triplet observed by RESIK

We present the observations of He-like Ar triplet lines obtained by RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios between triplet lines of lower Z elements is known to provide useful diagnostics of plasma conditions within the emitting source. Here, we investigate whether triplet line ratios are useful for interpretation of higher Z element spectra. A high sensitivity, low background and precise absolute calibration of RESIK allow to consider in addition also the continuum contribution. This provides a way to determine the Ar absolute abundance from the observed triplet component ratios. The method is presented and the results are shown for two selected flares. Derived values of Ar absolute abundance for these flares are found to be similar: 2.6 × 10 −6 and 2.9 × 10 −6. They fall in the range between presently accepted Ar photospheric and coronal abundances.

X-Ray Spectrum of Sagittarius A East

Abstract Sgr A East is a young SNR located in the Galactic Center (GC) region. Since the GC region is occupied by diffuse X-ray emission (GCDX) with a strong 6.7 keV line, an estimation of the GCDX is crucial to study the X-ray spectrum of Sgr A East. The flux and spectrum of the GCDX are found to be smoothly distributed around and across Sgr A East, and hence a reliable GCDX subtraction can be made. This paper presents the X-ray spectrum of Sgr A East with the XIS on board Suzaku. In addition to the previously reported $\mathrm{K}\alpha$ lines from S XV, Ar XVII, Ca XIX, and Fe XXV (all He-like atoms), we found $\mathrm{K}\alpha$ lines from S XVI, Ar XVIII, Fe XXVI (all hydrogenic atoms), and Ni XXVII (He-like), $\mathrm{K}\beta$ lines from S XV, Ar XVII, and Fe XXV, and a $\mathrm{K}\gamma$ line from Fe XXV. Plasma diagnostics using these lines revealed the presence of at least a two-temperature plasma. The overall spectrum can be fitted with a two-temperature ($\sim 1.2 \,\mathrm{keV}$ and $\sim 6 \,\mathrm{keV}$) plasma in ionization equilibrium plus a power-law component.

Electron impact excitation of Ar XVII

Energies for the lowest 49 levels among the 1s 2 and lsn (n = 2-5) configurations of Ar XVII have been calculated using the GRASP code of Dyall et al. (1989, Comput. Phys. Comm., 55, 424). Additionally, radiative rates, oscillator strengths, and line strengths are calculated for all electric dipole (El), magnetic dipole (Ml), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Furthermore, collision strengths have also been calculated for all the 1176 transitions among the above 49 levels using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2005, Comput. Phys. Commun., in preparation), over a wide energy range up to 580 Ryd. Resonances have been resolved in the threshold region, and effective collision strengths have been obtained over a wide temperature range up to log T e = 7.2 K. Comparisons are made with the limited results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 0.1%, whereas results for other parameters are probably accurate to better than 20%.

The BeppoSAX 0.1–18 keV spectrum of the bright atoll source GX 9+1: an indication of the source distance

We report the results of a long, 350 ks, BeppoSAX observation of the bright atoll source GX 9+1 in the 0.12-18 keV energy range. During this observation GX 9+1 showed a large count rate variability in its lightcurve. From its color-color diagram we selected six zones and extracted the source energy spectrum from each zone. We find that the model, composed of a blackbody plus a Comptonized component absorbed by an equivalent hydrogen column of ~1.4 ? 1022 cm-2, fits the spectra in the energy range 1-18 keV well; however, below 1 keV a soft excess is present. We find that the spectrum of GX 9+1, in the 0.12-18 keV energy range, is well fitted by the model above, if we use an equivalent hydrogen column of ~0.8 ? 1022 cm-2, together with several absorption edges from ionized matter (O VII, O VIII, Ne IX, Ar XVII, and Ca XX) and an absorption line from Si XIV. From the study of these features we deduce that the electron density of the plasma and the equivalent hydrogen column density associated with the ionized matter is ~1012 cm-3 and ~1023 cm-2, respectively, at a distance from the central object of r ~ 1011 cm, while at larger distances the equivalent hydrogen column density associated to the ionized matter decreases down to ~1022 cm-2. The value of the equivalent hydrogen column of ~0.8 ? 1022 cm-2 associated to the interstellar matter implies that GX 9+1 is at a distance of 5 kpc, and not 8.5-10 kpc as usually assumed. This result implies that the atoll source GX 9+1 does not emit at the Eddington limit, as supposed until now, but has a luminosity of 6 ? 1037 erg/s in the 0.1-18 keV energy range, typical of LMXBs belonging to the bright atoll class.

Comparisons of laboratory wavelength measurements with theoretical calculations for neon-like through lithium-like argon, sulfur and silicon

Atomic structure codes have a difficult time accurately calculating the wavelengths of many-electron ions without the benefit of laboratory measurements. This is especially true for wavelengths of lines in the extreme ultraviolet and soft X-ray regions. We are using the low-energy capability of the Livermore electron beam ion traps to compile a comprehensive catalog of astrophysically relevant emission lines in support of satellite X-ray observations. Our database includes wavelength measurements, relative intensities and line assignments, and is compared to a full set of calculations using the Hebrew University – Lawrence Livermore Atomic Code (HULLAC). Mean deviation of HULLAC calculations from our measured wavelength values is is highest for L-shell transitions of neon-like ions and lowest for lithium-like ions, ranging from a mean deviation of over 500mÅ for Si V to 12mÅ in Ar XVI.

Identification of Three Weak Lines and Their Influences onDiagnostics of Electron Temperature and Density in Astrophysical Plasmas

By comparing of the spectra from the Chandra LETGs observation with thesynthetic spectra of argon, we identify two weak emission lines, thatis, the Ar XV 27.470 A line with transition2s3p 1P1−2s2 1S0 and the Ar XVI 27.872 A line withtransition 3d 2D3/2−2p 2P1/2, which blend with the NVII Lyα emission line. Severalsecond-order spectral lines are also identified, one of which isthe second-order Fe XVIII 14.534 A line withtransition 2p4(3P)3d 2F5/2−2p5 2P3/2, whichblends with theinter-combination line of He-like N VI. In order to study the effects ofthese new identified weak lines on the electron temperature anddensity, we diagnose the two parameters using the intensity ratioof triplets of the He-like N VI and that of resonance lines of H-and He-like N. In the literature, there is a discrepancy of thetemperatures deduced from N VI from other He-like ions, suchas C V and O VII. The discrepancy disappears after thecontribution of these weak lines is taken into account.

High‐Resolution X‐Ray Spectra of the Brightest OB Stars in the Cygnus OB2 Association

The Cyg OB2 association contains some of the most luminous OB stars in our Galaxy, the brightest of which are also among the most luminous in X-rays. We obtained a Chandra High Energy Transmission Grating Spectrometer observation centered on Cyg OB2 No. 8A, the most luminous X-ray source in the association. Although our analysis focuses on the X-ray properties of Cyg OB2 No. 8A, we also present limited analyses of three other OB stars (Cyg OB2 Nos. 5, 9, and 12). Applying standard diagnostic techniques as used in previous studies of early-type stars, we find that the X-ray properties of Cyg OB2 No. 8A are very similar to those of other OB stars that have been observed using high-resolution X-ray spectroscopy. From analyses of the He-like ion fir emission lines (Mg XI, Si XIII, S XV, and Ar XVII), we derive radial distances of the He-like line emission sources and find that the higher energy ions have their lines form closer to the stellar surface than those of lower ion states. These fir-inferred radii are also found to be consistent with their corresponding X-ray continuum optical depth unity radii. Both of these findings are in agreement with previous O star studies and again suggest that anomalously strong shocks or high-temperature zones may be present near the base of the wind. The observed X-ray emission-line widths (HWHM ~ 1000 km s-1) are also compatible with the observations of other O star supergiants. Since Cyg OB2 No. 8A is similar in spectral type to ? Pup (the only O star that clearly shows asymmetric X-ray emission-line profiles with large blueshifts), we expected to see similar emission-line characteristics. Contrary to other O star results, the emission lines of Cyg OB2 No. 8A show a large range in line centroid shifts (~-800 to +250 km s-1). However, we argue that most of the largest shifts may be unreliable and the resulting range in shifts is much less than those observed in ? Pup. Although there is one exception, the H-like Mg XII line, which shows a blueshift of -550 km s-1, there are problems associated with trying to understand the nature of this isolated large blueshifted line. To address the degree of asymmetry in these line profiles, we present Gaussian best-fit line profile model spectra from ? Pup to illustrate the expected asymmetry signature in the ?2 residuals. Comparisons of the Cyg OB2 No. 8A best-fit line profile residuals with those of ? Pup suggest that there are no indications of any statistical significant asymmetries in these line profiles. Both the line shift characteristics and lack of line asymmetries are very puzzling results. Given the very high mass-loss rate of Cyg OB2 No. 8A (approximately 5 times larger than previous Chandra-observed O supergiants), the emission lines from this star should display a significant level of line asymmetry and blueshifts as compared to other OB stars. We also discuss the implications of our results in light of the fact that Cyg OB2 No. 8A is a member of a rather tight stellar cluster, and shocks could arise at interfaces with the winds of these other stars.

First Determinations of Differential Emission Measure Distribution from RESIK X-ray Spectra

RESIK Bragg spectrometer aboard CORONAS-F solar observatory collected spectra of hundreds of solar flares in the unique spectral range between 3.3 A and 6.1 A. The instrument’s absolute and relative calibrations are now finished which allows for the first time to interpret the observations in terms of the differential emission measure (DEM) distribution. With known DEM shape it is possible to derive and study in detail flaring plasma composition and energy balance. Here we report results of using an improved Maximum Likelihood iterative algorithm (WithbroeSylwester) for determination of the DEM distributions for 7 January 2003 flare at 23:30 UT. The study is based on the absolute flux values observed in a number of strong Hand He-like transitions of K xviii, Ar xviii, Ar xvii, S xvi, S xv, Si xiv and Si xiii ions. In this respect, we use line and continuum X-ray emissivities as provided by CHIANTI package from SolarSoft.

Energy Levels and Radiative Rates for Li-like Ar XVI and Fe XXIV

Energy levels for transitions among the lowest 24 fine-structure levels belonging to the 1s2nl (n ≥ 5) configurations of Li-like Ar XVI and Fe XXIV have been calculated using the fully relativistic GRASP code. Oscillator strengths, radiative rates and line strengths have also been generated among these levels for the four types of transitions: electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2). Comparisons are made for the electric dipole transitions with other available results, and the accuracy of the present data is assessed.

Experimental study on ion temperature behaviours in ECH, ICRF and NBI H2, He and Ne discharges of the Large Helical Device

Ion heating experiments have been carried out in the large helical device using ECH (82.5, 84.0, 168 GHz, ⩽1 MW), ICRF (38.5 MHz, ⩽2.7 MW) and NBI (H° beam: 160 keV, ⩽9 MW). The central ion temperature has been observed from the Doppler broadening of Ti XXI (2.61 Å) and Ar XVII (3.95 Å) x-ray lines, which are measured using a newly installed crystal spectrometer with a charge-coupled device. Recently, in ECH discharges, on-axis heating became possible. As a result, a high Te(0) of 6–10 keV and a high ion temperature of 2.2 keV were obtained at ne = 0.6×1013 cm−3. A clear increment of Ti was also observed with the enhancement of the electron–ion energy flow when the ECH pulse was added to the NBI discharge. These results demonstrate the feasibility towards ECH ignition. A clear Ti increment was observed also in ICRF discharges at low density ranges of (0.4–0.6)×1013 cm−3 with appearance of a new operational range of Ti(0) = 2.8 keV > Te(0) = 1.9 keV. In low power ICRF heating (1 MW), the fraction of bulk ion heating is estimated to be 60% of the total ICRF input power, which means Pi>Pe. Higher Ti(0), up to 3.5 keV, was obtained for a combined heating of NBI (<4 MW) and ICRF (1 MW) at density ranges of (0.5–1.5)×1013 cm−3. The highest Ti(0) of 5 keV was recorded in Ne NBI discharges at ne<1×1013 cm−3 with the achievement of Ti(0)>Te(0), whereas the Ti(0) remained at relatively low values of 2 keV in H2 and He NBI discharges due to less Pi. The main reasons for the high Ti achievement in the Ne discharges are: (1) 30% increment of deposition power, (2) increase in Pi/ni (five times, Pi/ni≫Pe/ne, Pi<Pe) and (3) increase in τei (three times). The obtained Ti(0) data can be plotted by a smooth function of Pi/ni. This result strongly suggests that the ion temperature increases even in the H2 discharge if the Pi can be raised up.