Rapid ionization of Cs vapor in a heat pipe at 0.05 torr was achieved by pumping the 6s 2S½ – 7p 2P½ transition (f=0.007)1 with a flash-pumped dye laser at 4593.2A and I MW power output. Photoabsorptian initiated at the end of the laser pulse(≃ 0.5/s) showed the 5p5ns and nd series below and above the 5p52P3/2 threshold at 535.4A. Broad Beutler - Fano resonances appeared in the d series above threshold. The spectrum was recorded photographically on a 10.7m grazing incidence spectrograph using a continuum background generated by a BRV high-voltage spark source with a uranium anode. We will compare the line-shapes and the quantum defect (Lu-Fano2) plot with the predictions of a relativistic random phase calculation.

In an experiment to measure emission line intensities from the Belike ion Ne VII (Lang 1983), the intensity ratio I(2s3s3S−2s3p3P)/I(2p23P−2s3p3P) was found to be a factor six larger than predicted from the ratio of the theoretical spontaneous radiative transition probabilities (A values). Indeed, to reconcile the Ne VII experiment and theory in several respects it was suggested also that in Be-like C III the theoretical ratios I(2s3s1 S−2s3p1P)/I(2p21D−2s3p1P) was about a factor three too low.

The same apparatus was used to measure A value ratios in Be-like N IV and 0 V. Briefly the 40 kJ θ-pinch plasma source was viewed radially using a m Ebert and a l m grazing incidence photoelectric spectrometer. The m Ebert was intensity calibrated from 7300 Å to 3600 Å using a tungsten filament lamp, and from 3800 Å to 2500 Å using a deuterium lamp, both lamps having been calibrated by NPL. As described fully by Lang (1983), the branching-ratios method was used to calibrate the front exit slit of the grazing incidence instrument in the wavelength range 88 Å to 500 Å. Only Li-like line pairs of those listed in that paper were used with the addition of the C IV doublets 2s2S−3p2P (312.4 Å) and 3s2S−3p2P (5801.33 Å, 5811.98 Å). The H-like ion He II 1–4 transition (243.0 Å) and 3–4 transition (4685.7 Å) were used to cross-check the calibration. As shown in the figure, the He II result agrees excellently with the calibration as defined from the Li-like lines.

We have begun a program to measure oscillator strengths of autoionizing resonances that result from a transition in the VUV between a laser excited initial state and a final state in which a core electron is promoted. These measurements demonstrate a new technique to combine synchrotron radiation, laser pumping, and photoelectron spectroscopy.

Measurements of the energy positions of autoionizing resonances have been honed to a fine art over the past 50 years. Total cross section measurements and the parameters that describe autoionizing resonances have been determined. Most of these studies have been made from the dipole allowed ground state. Recently autoionizing resonances have been observed from excited initial states and from ion initial states. We have heard several talks, at this meeting which described some of this type of research. In the measurements to be described in this paper, laser radiation is combined with synchrotron radiation, as shown schematicaly in Figure 1, to study the photoionization from excited initial states to continuum final states or to autoionizing final states. Continuum radiation from the Aneau de Collisions d’Orsay (ACO), which is installed at the Universite de Paris-Sud, in Orsay France, is monochromatized by a toroidal grating monochromator (TGM) and is focused by a toroidal output mirror on to a weakly collimated sodium beam emanating from a furnace mounted on the axis of a cylinderical mirror analyzer (CMA). This electron spectrometer is used to study the kinetic energy distribution of the ejected photoelectrons produced by the interaction of the photon beam with the focused synchrotron radiation.

The physics of multicharged ions has considerably developped during the last few years. Aside from its fundamental interest and its motivation for fusion research with Tokamak devices where charge exchange involving highly charged impurities are important, this new effort in this direction is due to the development of new sources of highly charged ions.

We report results concerning spectroscopic study of radiative transitions observed during the collision between multicharged N5+ ions with a helium or molecular hydrogen target. Nx+ ions are produced with the E.C.R. ion source in Grenoble (Geller and Jacquot 1981). The N5+ ions are then selected with two 168° bending magnets and finally sent into the target chamber where they collide either with He or H2 gas. Spectra are observed with a grazing incidence (82°) spectrometer equipped with photon detection.

The SOLEX X-ray spectrometers on the USAF P78–1 satellite have measured solar X-ray spectra in the 5.5–12Å range under a variety of flaring and nonflaring conditions. High sensitivity, obtained by summing data from several successive spectral scans, enabled the detection of 80 lines, 17 of which remain unidentified. The stronger lines were observed with individual scans during the course of flare development. This capability, along with the use of nonflare spectra, facilitated the identification of several lines. The lines of Fe XXII - XXIV, present in hot flare plasmas, are prominent in this wavelength range. For many of these lines, theoretical and observed line strengths will be compared. Diagnostically useful line ratios were evaluated for the helium-like species Mg XI, Al XII, and Si XIII. The density-sensitive R ratio was consistent with theoretical calculations of the low-density limiting value for Mg XI and Si XIII, the only species for which it was evaluated. In all cases the G ratio was below calculated values.

The SOLEX bragg crystal spectrometer experiment on the P78-1 satellite (Landecker, McKenzie and Rugge, 1979) has been used to determine accurate flux ratios of several strong solar Fe XVII x-ray emission lines in the ~ 15 to ~ 17 Å wavelength region. The ratios chosen were selected because the lines used permitted an accurate determination of the ratios both from the aspect of counting statistics as well as the lack of interference from other lines of comparable strength. Observations for a variety of conditions of solar activity, ranging from quiet conditions to large solar flares, are presented. For these observations intensity variations of a factor of about 60 were observed for the Fe XVII lines. Variations of a factor of almost 800 were observed for the Fe XVIII line at 14.2 Å. The observed ratios of the Fe XVII lines are compared to the theories of Loulergue and Nussbaumer (1975) and Smith, Raymond, Mann and Cowan (1984).

The XUY (90–150 Å) and X-ray (10–25 Å) spectra of solar flares are rich in lines from the highly ionized iron ions. Atomic data have been calculated for Fe XVIII (Bhatia, unpublished), Fe XIX (Loulergue et al., 1984, Bhatia and Mason, 1984), Fe XX (Mason and Bhatia, 1980, 1983), Fe XXI (Mason et al., 1979), Fe XXII (Mason and Storey, 1980), Fe XXIII (Bhatia and Mason, 1981), Fe XXIV (Hayes, 1979). The University College London computer package was used. This consists of an atomic structure code (SUPERSTRUCTURE, Eissner et al., 1974); a ‘distorted wave’ electron scattering program (COLLDW, Eissner and Seaton, 1972); a ‘Bethe’ approximation electron scattering program (Burgess and Shoerey, unpublished); a program for obtaining electron collision strength in pair coupling from R matrices in LS coupling (JAJOM, Saraph, 1972); a proton scattering program (Bely and Faucher, 1970) and a program for obtaining level populations and intensity ratios.

Results of a high spectral resolution observation of the RS CVn binary σ Cr B, made with the Focal Plane Crystal Spectrometer (FPCS) on the Einstein Observatory, are reported. A spectral scan in the 800–840 eV interval shows clear presence of an X-ray emission line at 826 eV identified with the 1S0 − 1P1 transition of Fe XVII. A prominent peak at 1007 eV in the scan band 987–1013 eV is attributed to a blend of lines due to Fe XVII and Fe XXI. Using the observed line fluxes and the Raymond-Smith model, best fit values of corona temperature and volume emission measure, with associated 90% confidence level uncertainties, are derived to be (6.9 ± 0.8) × 106 K and (1.7 ± 0.7) × 1053 cm−3, respectively. Pressure and density of the X-ray emitting plasma and loop length are deduced by applying a Constant Pressure Coronal Loop Model.

The transition region exhibits dynamic changes during solar flares. To understand the energy release and transport processes in solar flares, it is important to determine observationally the physical conditions in the flare transition region plasmas, which emit in the UV wavelength ranges. During the Solar Maximum Mission (SMM) we observed many flares in the UV emission lines of Si IV (1402 Å) and 0 IV (1401 Å) using the Ultraviolet Spectrometer and Polarimeter (Woodgate et al. 1983). In this paper we present the Si IV/O IV flare observations, in particular the dynamic evolution of the transition zone plasmas (~ 105 K). We also studied the temporal and spatial correlations between the impulsive UV and hard X-ray bursts.

The measurement of transition energies in highly charged ions represents an important test of quantum electrodynamics (QED) in strong fields. The OED contributions to the hydrogenic transition energies increase as (αZ)4, where α is the fine structure constant and Z is the atomic number. Transitions in hydrogenic ions of sulfur, chlorine, argon, and iron have previously been measured to a precision of 100 ppm or better. These measurements are in satisfactory agreement with accurate calculations of the energy levels, and this confirms the calculation of the QED contributions to the energy levels of one-electron ions.

We discuss the Mg XII Lyα line profile measurements obtained, by means of Bragg crystal spectrometer aboard INTERCOSMOS 7 satellite. The design of this spectrometer allows to clearly resolve both components α½ and α3/2) of the Lyα spin doublet. The intensities of each of these components we derived by means of fitting two Voigt profiles to the measured Mg XII Lyα shape. More than 100 spectra were analyzed in this way providing the statistical information on the value of intensity ratio . Derived average value of a is close to the theoretically expected 0.5, but in many cases the value of a is significantly different from 0.5 (both lower and higher values occur). We present examples of the fit and the histograms showing correlations of a value with the values of other flare parameters. Present analysis consist the observational part of the larger paper under the preparation with Prof. R.W.P. McWhirter theoretical group.

In the past years several space missions have been proposed for the study of the Sun and of the Heliosphere. These missions were intended to clarify various different aspects of solar physics. For example, the GRIST (Grazing Incidence Solar Telescope) mission was intended as a means to improve our knowledge of the upper transition region and low corona through the detection of the solar EUV spectrum with a spatial resolution larger than in previous missions; the DISCO (Dual Spectral Irradiance and Solar Constant Orbiter) and SDO (Solar Dynamics Observatory) missions were proposed to gat observational data about the solar oscillations better than those obtained from ground based instruments; the SOHO (Solar and Heliospheric Observatory) mission was initially proposed to combine the properties of GRIST with the study of the extended corona (up to several radii of heliocentric distance) by observing the scattered Ly-alpha and OVI radiation, which was also the basis of the SCE (Solar Corona Explorer) mission proposal; the development of the interest about the variability of the Sun, both in itself and for its consequences in the history of the Earth, led to propose observations of the solar constant (included in DISCO).

A short review of the atomic and molecular data which are necessary for astrophysics researches is presented. A list of atomic data is described which was chosen by first Soviet colloquiuun on atomic data in astrophysics.

Ratios of intensities of spectral lines produced in the radiative decay of collisionally-excited levels of atomic ions are versatile indicators of electron density in astrophysical plasmas when one of the lines involves a metastable level (see the review by Feldman 1981 and references therein). Radiative transition probabilities (A-values) and electron excitation cross sections are necessary for accurate, quantitative analyses of these plasmas. The work reported here is part of a program of measurements of astrophysically interesting A-values and radiative lifetimes (see the review by Smith et al. 1984); until we began, such anaylyses of astrophysical plasmas depended upon unconfirmed calculated A-values.

The necessity for understanding molecular formation and destruction processes occurring in astrophysical environments is well known. Accurate molecular data are of critical importance in formulating models of such diverse regions as interstellar clouds and planetary and stellar atmospheres. With this in mind we have devised an experimental method and constructed an apparatus for the determination of cross sections as well as the kinetics for photodissociation processes in chemically unstable neutral molecules. Similar experimental methods have been independently developed by de Bruijn and co-workers and by Chen et al.

The analysis of impurity radiation from Tokamak plasmas is one of the most important diagnostics, allowing the measurement of the impurity concentrations, radiation losses and particle transport studies. This study requires simultaneous time-resolved observation of spectral lines from many ionization states for each element. The most intense and important lines are the He and H-like resonance transitions of Oxygen and Carbon and Δn = 0, 1 transitions of highly ionized metallic impurities. These emmissions have been recorded on PLT and TFTR tokamaks by means of a soft X-ray multichannel spectrometer (SOXMOS).

Allowed 2s22pk − 2s2pk+1 transitions in the F I- B I-like ions of elements with Z ≥ 20 are often observed in spectra of high-temperature (Te ≥ 107 K) laboratory and astrophysical plasmas. Calculations of level populations in these ions are important in the interpretation of measured intensities of these lines for plasma diagnostics. Impurity ion densities and radiated power losses in tokamak plasmas, and the emission measure of astrophysical sources, can be derived from spectroscopic measurements using level population calculations. Certain line-intensity ratios can be used to measure the electron density in astrophysical plasmas; this technique may also be useful in some low-density laboratory plasmas. It is therefore important to experimentally check the level populations in high-Z ions using spectra from a well-diagnosed laboratory plasma, such as that of a tokamak. This has been previously done only for some transitions in Fe XVIII - Fe XXII (Suckewer and Hinnov 1979).

The major goal of this research program is to determine, experimentally, accurate absolute cross sections for dielectronic recombination (DR) in multiply and singly charged atomic ions. Our initial measurements of DR in C3+ are designed to provide a “bench mark” cross section for a simple atomic system. The experiment determines energy averaged DR cross sections for a well defined process involving a specific stabilizing transition. The fields in the region where dielectronic recombination occurs can be made small (≅ 0.25 V/cm) in order to minimize the effect of Stark mixing which is expected to enhance the DR process. We are presently adding the capability to apply known mixing fields up to 5 V/cm in the electron-ion interaction region of our apparatus.

The calculation of atomic properties is plasma is critically dependent on the form of the ion-electron interaction potential. In the case of weak collisions in a low density ionized gas, the screening of the ion under consideration by surrounding plasma is adequately described by the Debye-Hückel potential (see, e.g., Weisheit, 1983). If the plasma is very dense, the perturbation approximations leading to the Debye form break down and other techniques must be employed to incorporate additional correlative effects. The transition from classical to this strongly coupled plasma occurs when the parameter , where is the mean charge per ion, , and ro is the ion-sphere radius, is greater than about one.

In order to calculate bremsstrahlung cross sections in plasmas, an atomic potential which includes the effects of the surrounding plasma is required. For the high ρ - T conditions we are considering (ne = 1025 cm−3, T = 500 ev), plasma correlative effects are important. In these strongly coupled plasmas, the Debye-Huckel potential is irrelevant and not considered here. The statistical Thomas-Fermi (TF) potential (Feynmann, Metropolis, and Teller, 1949) is known to be correct at very high densities but does not contain correlation information. A semiclassical treatment of correlations that accurately reproduces results of numerical simulations of strongly coupled plasmas is the hypernetted chain (HNC) approximation to the hierarchy of equations describing density distributions (Hansen and McDonald, 1981). The method generates many-body distributions using an analytic two-body interaction that successfully approximates quantum effects at short distances. These distributions are used in the Poisson equation to find the effective potential (Cauble, Blaha, and Davis, 1984). An alternative method (Gupta and Rajagopal, 1982) of including correlations is to treat them in a quantum mechanical manner, taking into account ion correlations as well as electron exchange and correlation; this is done in density functional theory (DFT), where electron wavefunctions and the effective potential which is used here are obtained self-consistently (Dharma-wardana and Perrot, 1982; Perrot and Dharma-wardana, 1984). Comparison of these methods can be found elsewhere (Cauble, Gupta, and Davis, 1984). These potentials for aluminum at 1025 cm−3 and 500 eV are displayed in Fig. 1.