K. Słabkowska

Observation of L-X-ray satellites and hypersatellites in collisions of O and Ne ions with Mo and Pd

Abstract The satellite structure of Lα 1,2 and Lβ 1 X-ray transitions in 42 Mo and 46 Pd induced by an impact of O and Ne ions with energies 178–376 MeV have been studied with a high-resolution von Hamos crystal spectrometer. The observed M-shell satellites of the diagram Lα 1,2 and Lβ 1 lines are affected mostly by one- and two-vacancy configurations for oxygen ions and much more complex multi-vacancy configurations for neon impact. The L-shell hypersatellites are clearly observed in the measured spectra, both for Lα 1,2 and Lβ 1 X-ray transitions. The spectra are compared with the predictions of the multi-configuration Dirac–Fock (MCDF) calculations performed for up to two additional vacancies. Such MCDF calculations reproduce the main features of the M-shell satellite structure observed for oxygen ions, but they fail to describe the X-ray spectra measured for neon ions. Clearly, more complex multi-vacancy configurations have to be included in the MCDF calculations to achieve quantitative agreement in this case. The measured X-ray satellite structure for neon ions is thus interpreted by means of a simplified binomial model based on the average MCDF X-ray shifts and independent electron picture of multiple ionization of atoms by ion impact.

Modeling of the L and M x-ray line structures for tungsten in high-temperature tokamak plasmas

We present the results of modeling of the L and M x-ray line structures for tungsten in high-temperature plasmas predicted with temperatures relevant to large tokamaks including the Joint European Tokamak and the future International Thermonuclear Experimental Reactor. The simulations have been performed using the Flexible Atomic Code within the framework of the collisional–radiative (CR) model. For L x-ray lines, our results predicted for various levels of CR model sophistication have been compared with the spectrum measured using the electron beam ion trap (EBIT) calorimeter spectrometer at the Livermore SuperEBIT that constitutes a rigorous atomic benchmark for tokamak plasmas. In the case of M x-ray lines, we have reproduced the experimental SuperEBIT spectra as a superposition of theoretical contributions for different ions. The obtained results enable us to propose an approach allowing the decomposition of registered experimental tungsten spectra produced in tokamaks into the theoretically predicted contributions, corresponding to different degrees of ionization.

Influence of multiple outer-shell electron stripping on the Kα and Kβ x-ray energies of iridium

We present theoretical predictions for iridium Kα1,2, Kβ1,3 and Kβ2 energy shifts as a function of outer-shell stripping, evaluated using the multiconfiguration Dirac–Fock method including Breit interaction and QED corrections. The energy shifts are consistent with the K-lines emitted by the plasma made in the plasma-filled rod pinch, and potentially relevant to diagnostics of high-energy density laser-produced plasmas as studied in connection with the National Ignition Facility.

Effect of L- and M-shell ionization on the shapes and parameters of the K X-ray spectra of sulphur

Abstract Extensive single-configuration Dirac–Fock (DF) calculations (within the multiconfiguration DF method) have been performed for sulphur to explain the influence of removing electrons from L and M shells on the shapes and parameters (the average Kα and Kβ transition energies and the values of Kβ/Kα intensity ratio) of its K X-ray spectra. For Kα and Kβ diagram lines and each type of L- and M-satellite lines, the theoretical stick spectra (line positions with their relative intensities) have been presented. The theoretical results obtained can be used for interpreting the measured shapes and parameters of the K X-ray spectra of highly ionized swift sulphur projectiles passing through various foils. They can also be very helpful in interpreting various sulphur target K X-ray spectra induced by photons and different projectiles recorded by high-resolution crystal spectrometer or lower-resolution detector.

Diagnostics of plasma based on K, L and M x-ray line positions

Ionization can affect the energy of characteristic x-ray lines sufficiently for a single line to be of value in plasma diagnostics. Recently, the ionization of a hot, dense tungsten plasma was determined from a detailed analysis of a single, highly resolved L x-ray line, and in an iridium plasma the change in energy of a single K x-ray line confirmed the theoretical estimate of the ionization. Diagnosing plasmas by these ionization energy shifts depends essentially on computations that can now be performed with sufficient accuracy, e.g. with the multi-configuration Dirac?Fock method. Besides extending earlier computations on the influence of outer-shell ionization on the energy of tungstens K and L x-ray lines, this paper also presents the effect of ionization on the lower-energy M x-ray lines and a discussion of their relative merits for plasma diagnostics.

Influence of multiple outer-shell electron stripping on the Lα, Lβ and Lγ x-ray energies of tungsten

Gradually stripping tungsten of its outer-shell electrons tends to increase the x-ray energies of the various Lα, Lβ and Lγ x-ray lines. For the Lα1 and Lβ1 lines the energy change is sometimes negative but always less than 10 eV when the ionization remains below W30+; other lines increase their energy approximately quadratically with ionization level. Beyond W30+ the increase is dramatic and some lines blue-shift many hundreds of eV already at W40+. The computations are carried out with a multiconfiguration Dirac–Fock method that includes the Breit interaction and some QED corrections. The results are relevant to high-resolution x-ray diagnostics of plasma produced by short-pulse lasers and to some pulsed power plasmas.

Highly excited states of sulphur projectiles inside a carbon target

Abstract The satellite and hypersatellite K X-ray lines emitted by sulphur projectiles (with energies 9.6, 16.0, 22.4, 32.0, 65, 79, 99 and 122 MeV) passing through carbon foils (with different thickness varying from 15 to 210 μg/cm2) have been measured using a Si(Li) detector. We use a theoretical model based on the single-configuration Dirac–Fock calculations and equilibrium charge state distribution to interpret the experimental K X-ray spectra parameters. For all projectile energies, we evaluate the probability of K-hole creation, the average population of L-shell, and the average population of the 3p and 4p subshells. In the case of 9.6–32.0 MeV beam energy we evaluate also the population of L and M shells of sulphur projectiles. For the energy range 65–122 MeV, we estimate the probability of appearance of the most important configurations. The lifetimes of the studied states is also deduced.

Observation of internal structure of the L-shell x-ray hypersatellites for palladium atoms multiply ionized by fast oxygen ions

An observation of the internal structure of the L-shell hypersatellite x rays resulting from the one-photon decay of L{sup -2} double-vacancy states in palladium multiply ionized by oxygen ions is reported. The Pd L{sub 3}{yields}M{sub 4,5} x-ray spectrum was measured with a von Hamos high-resolution crystal spectrometer. The complex shape of the observed spectrum could be interpreted in detail using relativistic multiconfiguration Dirac-Fock calculations. The relative intensities of the measured x rays were found to be in good agreement with semiclassical approximation calculations using relativistic Dirac-Hartree-Fock wave functions.

Vacancy rearrangement processes in multiply ionized atoms

We demonstrate that in order to interpret the x-ray satellite structure of Pd Lα1,2(L3M4,5) transitions excited by fast O ions, which was measured using a high-resolution von Hamos crystal spectrometer, the vacancy rearrangement processes, taking place prior to the x-ray emission, have to be taken into account. The measured spectra were compared with the predictions of the multi-con.guration Dirac-Fock (MCDF) calculations using the fluorescence and Coster-Kronig yields which were modiffed due to a reduced number of electrons available for relaxation processes and the effect of closing the Coster-Kronig transitions. We demonstrate that the vacancy rearrangement processes can be described in terms of the rearrangement factor, which can be calculated by solving the system of rate equations modelling the flow of vacancies in the multiply ionized atom. By using this factor, the ionization probability at the moment of collision can be extracted from the measured intensity distribution of x-ray satellites. The present results support the independent electron picture of multiple ionization and indicate the importance of use of Dirac-Hartree-Fock wave functions to calculate the ionization probabilities.

Modelling of the soft X-ray tungsten spectra expected to be registered by GEM detection system for WEST

Abstract In the future International Thermonuclear Experimental Reactor (ITER), the interaction between the plasma and the tungsten chosen as the plasma-facing wall material imposes that the hot central plasma loses energy by X-ray emission from tungsten ions. On the other hand, the registered X-ray spectra provide alternative diagnostics of the plasma itself. Highly ionized tungsten emits extremely complex X-ray spectra that can be understood only after exhaustive theoretical studies. The detailed analyses will be useful for proper interpretation of soft X-ray plasma radiation expected to be registered on ITER-like machines, that is, Tungsten (W) Environment in Steady-state Tokamak (WEST). The simulations of the soft X-ray spectra structures for tungsten ions have been performed using the flexible atomic code (FAC) package within the framework of collisional-radiative (CR) model approach for electron temperatures and densities relevant to WEST tokamak.