Single ionization of the Mo + ion for the ground and metastable configurations

Electron-impact ionization process is studied for subconfigurations of the ground (5 d 4 6 s ) and metastable (5 d 3 6 s 2 , 5 d 5 ) configurations of the W + ion using the scaled distorted wave (sDW) approximation. The excitation-autoionization (EA) channels corresponding to excitations from the 4 f , 5 d , and 6 s subshells are investigated. Convergence of the EA channels is determined by including the excitations up to shells with the principal quantum numbers n ≤ 30 and orbital quantum numbers l ≤ 5. Study demonstrates a significant contribution from the indirect process (∼20–40%) to the total ionization cross sections for the analyzed configurations. There is a good agreement between experimental data and theoretical results obtained for the 5 d 4 6 s and 5 d 3 6 s 2 configurations. The obtained results using subconfiguration averaged approach indicate that further level-to-level studies using sDW or more computationally intensive non-perturbative methods should focus on the 5 d 4 6 s and 5 d 3 6 s 2 configurations aiming to explain available measurements for the W + ion. Given its relatively low computational cost and reasonable accuracy, the sDW method proves to be a valuable tool for modeling ionization in fusion plasmas.

Absolute cross sections for electron impact single and double ionization of Niq+ ions (q = 10, 11, 13 and 15) have been measured for energies from threshold to about 5 keV. Experimental results for Ni11+, Ni13+ and Ni15+ are in good agreement with the calculations of Pindzola et al, obtained in the average configuration distorted-wave approximation for the 3s23pn (n = 5, 3 and 1) ground configurations, respectively. The Ni10+ results show a significant ionization signal below the ground state [Ne]3s23p6 threshold due to ions formed in the metastable configuration [Ne]3s23p53d in the parent ion beam. The theoretical calculations including direct ionization and excitation- autoionization’from both the ground and the excited configurations underestimated the cross section. The difference is probably due solely to the 3s → nl excitations. In this isonuclear sequence, the whole results shows that ions with an odd number of electrons behave differently from ions with an even number. Our measurements show clearly that double ionization is dominated by L-shell ionization followed by autoionization.

Total radiated line power coefficients for ions of medium to heavy weight elements, called coefficients in the atomic data and analysis structure, have been improved by algorithmically optimising the selection of configuration sets that underpin the calculation to include the most important radiating transitions driven by both the ground and metastable configurations and to establish and limit the error of truncation. The optimised calculations typically differ from Pütterich by 20%–30% with truncation error . Further appraisal of error due to atomic level bundling, atomic structure and collision strength calculation methods has been carried out. It is shown that bundling to configurations is accurate to for all ions except those with closed-shell ground configurations which give errors up to a factor 2–3. For near neutral, closed-shell ions, plane-wave Born collision strength calculations, which omit spin-change, give substantial error in comparison with distorted-wave calculations of . For highly charged ions, spin-system breakdown reduces the error in the markedly, typically . The error introduced by the atomic structure codes used here, autostructure and the Cowan code, is probably limited to .

Absolute cross sections for electron-impact single ionization of ${\mathrm{Kr}}^{8+}$ and ${\mathrm{Xe}}^{8+}$ ions were measured for energies below the ionization thresholds to 1500 eV using the crossed-beams method. A significant fraction of the ${\mathrm{Kr}}^{8+}$ and ${\mathrm{Xe}}^{8+}$ ion beams were in metastable configurations. Configuration-average distorted-wave calculations for ions in the ground and first-excited configurations are compared to the experimental data. For both ions in this study, the excitation-autoionization contribution to the total ionization cross section is found to be much larger for ions in the first-excited configuration, which includes metastable levels, than for the ground-state ions. Maxwellian rate coefficients were calculated for ${\mathrm{Kr}}^{8+}$ and are compared to published results.

We model structural transitions of small-size Wigner crystals in laterally compressed two-dimensional traps. Ground and metastable configurations are calculated and their transformations are linked to conspicuous changes in the heat capacity of the system. We show that various types of structural transitions are reflected by characteristic features in the behavior of the heat capacity. For deeper understanding, results produced by the Monte Carlo numerical calculations are compared to predictions of simple one-dimensional models.

Spherical dust clusters composed of several concentric shells are experimentally investigated with particular interest on transitions between different configurations and transitions of particles between different shells. Transitions between different ground and metastable configurations are frequently observed. The experimental analysis allows us to derive the energy differences of different configurations from particles traveling between shells. The observed transitions and transition probabilities are compared to molecular dynamics simulations.

Absolute cross sections have been measured from below threshold to 1500 eV for electron-impact single ionization of chromium ions in initial charge states 6+, 7+, 8+, and 10+. The measurements utilized the Oak Ridge National Laboratory Electron Cyclotron Resonance ion source and electron-ion crossed-beams apparatus. The lowest three charge states, which have 3${s}^{2}$3${p}^{n}$ ground-state electron configurations, all exhibit ionization onsets at lower energies than expected for ground-state ions, indicating the presence of ions in metastable configurations in the incident beams. Significant contributions to the total cross sections by excitation autoionization are observed for each ion. The present measurements are compared to calculations of direct ionization from the Lotz formula, and the ${\mathrm{Cr}}^{10+}$ measurements are compared to previous data for the isoelectronic ion ${\mathrm{Ni}}^{14+}$.

The electron-impact single ionization of low-charged Ti ions was studied both experimentally and theoretically. Absolute cross sections for ions in charge states q = 1 to 6 except 3 were measured using a crossed-beams technique as well as calculated with the configuration-average distorted-wave method, including both direct ionization and excitation-autoionization contributions. For charge states q = 4, 5 and 6, the measurements are in good agreement with the calculations considering that large components of the incident ion beam were in metastable configurations. The cross sections for single ionization of and were determined in part with a high-resolution energy-scan method. Besides contributions of excitation-autoionization mechanisms, a remarkable number of structures arising from resonant-excitation double-autoionization (REDA) processes could be observed.

Contributions of resonant excitation double auto-ionization to the electron-impact single-ionization cross-sections of Sn12+

Fundamental properties of finite 3D dust clouds, so called Yukawa balls are presented. In these systems the particles are arranged in concentric spherical shells (onion shells). Recent progress in diagnostic techniques is described which allows to reveal fundamental properties of such dust clusters. The dedicated formation of ground and metastable configurations of Yukawa balls are shown. Also self-induced transitions between different configurations are shown and discussed. The investigation of the ball structure and dynamics allows to derive a deep and fundamental understanding of the underlying particle and plasma processes.

Contribution of the metastable states to electron-impact single ionization for W7+

Electron-impact ionization for the levels of Fe3＋

The electron-impact single ionization cross section for W8+ ion has been calculated using flexible atomic code, employing the level-to-level distorted-wave approximation. This calculations takes into account contributions form both direct ionization (DI) and excitation autoionization (EA). However, the theoretical predictions, based solely on the ground state, tends to underestimate the experimental values. This discrepancy can be mitigated by incorporation contributions from excited states. We extended the theoretical analysis, including the contributions from the long-lived metastable states with lifetimes exceeding 1.5 × 10−5 s. We employed two statistical models to predict the fraction of ground state ions in the parent ion beam. Assuming a 79% fraction of parent ions in ground configuration, the experiment measurements align with the predictions. Furthermore we derived the theoretical cross-section for the ground state as correlated plasma rate coefficients, and compared it with existing data. Despite the uncertainty in our calculations, our results are still acceptable.

Electron-impact ionization of Sn4+

A joint theoretical and experimental investigation is made of the influence of long-lived metastable levels on the electron-impact single ionization of ${\mathrm{C}}^{2+}$. It is expected that our electron cyclotron resonance ion source produces a beam with 40% of the ${\mathrm{C}}^{2+}$ ions in the $1{s}^{2}2{s}^{2}\phantom{\rule{0.3em}{0ex}}^{1}S_{0}$ ground level and 60% in the $1{s}^{2}2s2p\phantom{\rule{0.3em}{0ex}}^{3}P_{0,2}$ excited levels. The comparison of nonperturbative close-coupling calculations with previous single-pass crossed beams and with our multiple-pass storage-ring measurements for the electron-impact ionization of ${\mathrm{C}}^{2+}$ is consistent with the predicted large metastable fraction. Reasonable agreement is found between the present time-dependent close-coupling, $R$-matrix with pseudostates, and converged-close-coupling ionization cross-section calculations for the ground and first excited configuration, and experimental measurement, assuming a 60% metastable fraction in the ion beam. Distorted-wave calculations are found to overestimate the ionization cross section from both the ground and metastable terms, compared with nonperturbative calculations, resulting in an overestimation of the resultant total cross section when compared with experiment. It is clear that collisional-radiative modeling of the evolution of atomic plasmas through the Be-like ionization stage will need to take into account the role of both ground and metastable levels.