V. A. Boiko

X-ray spectroscopy of multiply-charged ions from laser plasmas

Abstract Original results are reported on the observation and identification of spectra of multiply-charged ions in the range of λ ≈ 1.5–15 A, which corresponds to transitions with a range of principal quantum number n. The main part of the review consists of tables with about a thousand spectral lines, which have been mainly observed in laser-plasma radiation, as well as in the solar corona and other laboratory sources at an electron temperature Te≈107°K. The accuracy for the wavelengths (Δλ) is the following: Δλ is equal to ≈ 0.0005 A for λ ≈ 2.5 A and it is equal to ≈ 0.003 A for λ ≈ 15 A. The spectral lines are considered for the following transitions: 1-n type for [H]-like ions (Z = 11–16)and [He]-like ions (Z = 11–26); 2-n type for [Li]-like ions (Z = 19–26), [Be]-like ions (Z = 22–34) and [Ne]-like ions (Z = 26–42); 3-n type [Co]- and [Ni]-like ions (Z = 73). The line-list contains about four hundred wavelengths for multiply-charged iron L-ions (Fe(XVII)-Fe(XXIV)) and is presented with identification of some of the transitions. The wavelengths and intensities of satellites of the [H]-like ions and [He]-like ions, which are caused by transitions from the doubly-excited autoionization states 2l2l′ and 1s2l2L′ of [He]-like ions (Z = 11–16) and [Li]-like ions (Z = 11–26), respectively, are also considered.

The determination of laser plasma electron density by K spectra of multicharged ions

X-ray spectroscopic methods for the determination of electron densities Ne>1020 cm-3 in plasmas with high electron temperatures (Te>or approximately=0.2 keV) are reviewed. The methods considered are based on the following measurements of: (i) relative intensities of resonance and intercombination lines in spectra of He-like ions; (ii) relative intensities of satellite lines in spectra of H-like ions; (iii) relative intensities of H-like resonance doublet components; (iv) Stark broadening of the lines of H-like ions. All these methods have been used in experiments on plasma heating by focusing a laser beam on plane massive targets containing elements with nuclear charge Z=12-19. The density distribution in the plasma was measured within the limits of Ne=1018-1021 cm-3. The results obtained by all the methods are compared and the limits of application of the methods are determined.

Spectra of Be-like ions with nuclear charge Z=22,...,34 from laser-produced plasmas

Reports the classification of 220 spectral lines of Ti XIX, V XX, Cr XXI, Mn XXII, Fe XXIII, Co XXIV, Ni XXC, Cu XXVI, Zn XXVII, Ge XXIX and Se XXXI. The transitions identified are 1s22p2-1s22p3s, 1s22p2-1s22p3d, 1s22s2p-1s22s3s, 1s22s2p-1s22s3d, 1s22s2p-1s22p3p and 1s22s2-1s22s3p. These lines were emitted from laser-produced plasmas. Perturbation theory was used to calculate the wavelengths.

The observation of intercombination lines 1s3p 3P1→1s2 1S0 of multicharged He-like ions in laser-produced plasmas

The intercombination lines 1s3p 3P1 to 1s2 1S0 of the ions Mg XI, Al XII, P XIV, S XV and Cl XVI have been observed for the first time in the spectra of laser-produced plasmas. The wavelengths and relative intensities of such lines were measured. The identification of the observed lines was carried out by means of a comparison of the experimental wavelengths and intensities with the theoretical ones. The dependence of the relative intensities of such lines on the plasma parameters was investigated.

Identification of spectral lines of ions belonging to the F I isoelectronic sequence with nuclear charge Z=26-30, 32 and 34 from laser-produced plasmas

Spectra of the ions Fe XVIII to Zn XXII, Ge XXIV and Se XXVI of the F I isoelectronic sequence were obtained. Identification of 156 spectral lines for the ions considered was made on the basis of a comparison of experimental wavelengths and relative intensities with theoretical wavelengths and transition probabilities. The lines identified belong to transitions between configurations 1s22s22p5-1s22s22p43d and 1s22s22p5-1s22s22p43s. Theoretical calculations were made using the Hartree-Fock method with the inclusion of spin-orbit interaction.

Anomalous intensity ratios of the resonance to intercombination lines of He-like ions in Nd- and CO2-laser-produced plasmas

Anomalously small values of the intensity ratio alpha of resonance and intercombination lines of He-like ions have been observed in Nd- and CO2-laser-produced plasmas. The values of alpha obtained are explained via calculations using a non-stationary ionisation model for the plasma (overheated for CO2-laser plasma, and supercooled for expanding Nd-laser plasma). The measurements of the intensity ratio may be used to obtain information on the relative concentrations of H-, He-, and Li-like ions in the plasma. The results obtained allow one to answer the questions: when must the non-stationary character of the plasma ionisation state be taken into account for the observed spectra to be interpreted correctly; and when can one use more simple stationary models for the plasma concerned?.

New satellite structure of the solar and laser plasma spectra in vicinity of the L? (mg xii) line

Spectra in the narrow vicinity of the Mg xii resonance line at λ = 8.42 Å were obtained aboard the satellites ‘Intercosmos-4, -7’ and the rocket ‘Vertical-2’, as well as from laser-produced plasma. The high resolution in solar and laboratory spectra made it possible to reveal a new spectral structure close to the Lα (Mg xii) line from both short and long wavelength sides. The main features were observed in all the spectra and were interpreted as a single or group of dielectronic satellite lines due to 2l3l′ → 1s3l″ transitions in the He-like ions according to theoretical calculations which were carried out by means of relativistic Z-expansion technique. The derived electron temperature of the emitting volumes seemed to be ≈ 3 × 106 K for laser plasma and about 6 × 106 K for the solar flares studied. The latter value is in good agreement with the temperature estimated with the help of the resonance line-to-continuum intensity ratios.

Spectra of Ni XX and Cu XXI Belonging to the Fluorine Isoelectronic Sequence

Energy levels are presented for Ni XX and Cu XXI of the fluorine isoelectronic sequence. Behaviour of the energy structure of Fe XVIII through Zn XXII, Ge XXIV and Se XXVI was observed along the isoelectronic sequence. The spectra were obtained from laser-produced plasmas.

The determination of parameters of recombining laser-produced plasmas by means of X-ray spectroscopy

The investigation of expanding laser-produced plasmas has been carried out. X-ray spectra of multicharged F VIII and F IX ions were observed in the wavelength range lambda approximately 11-17 AA for the regions of expanding plasma, remote from the target surface by up to 10 mm. The calculations of resonance and intercombination line relative intensities were made, taking into account recombination of the population of ion levels in the case of sharply non-equilibrium plasma ionisation states. The results of the calculation are utilised for an investigation of expanding laser-produced fluorine plasmas.

Spectra of Multiply-Charged Lithium-Like Ions in a High-Temperature Plasma

Radiative-collisional model is used to investigate the kinetics excitation of levels 1s2nl, n ≤ 4 for the Li-like ions in a high-temperature plasma. It has been shown, that calculated relative line-intensities for ions from Ca XVIII to Br XXXIII enables one adequately to describe both laboratory and astrophysical plasmas. The calculated dependences of relative line-intensities on electron density were used for the diagnostics of plasma, as well as for identification of spectral lines of Li-like ions.