[en] Following the pioneering experiment of Dolder, Harrison and Smith nearly a half-century ago, measurements based on the colliding-beams technique became a major source of fundamental data on the electronic structure and interactions of ions. The subsequent development of powerful new sources of highly charged ions and large-scale national facilities such as heavy-ion storage rings and synchrotron light sources provided new applications for established techniques and inspired the development of new interacting-beams methods to take advantage of their unique capabilities. This paper focuses on experimental developments within the last decade involving multiply charged ions using crossed, inclined and merged beams. Examples are presented to highlight such experiments and their impact on our knowledge of the atomic structure of multiply charged ions as well as their interactions in plasmas. Atomic processes considered are elastic scattering, excitation, ionisation, recombination and electron transfer

[en] We have developed a number of methods for plasma diagnostics. Applications of these methods will include: extreme ultraviolet and x-ray imaging of hot plasma with temporal, spatial and spectral resolution; polarization measurements with spatial and temporal resolution; high-resolution spectroscopy of multicharged ions with temporal resolution. Currently-developed instruments include a pinhole camera with a glass capillary converter using as a hard x-ray filter; an extreme ultraviolet imager and spectrograph unit with multilayer mirrors; extreme ultraviolet polarimeters/spectrometers with glass capillary converters polarizing and focusing element; and a high resolution, a high-sensitivity x-ray or extreme ultraviolet spectrometer with focusing glass capillary converter that also serves as a high-transmission window for differential pumping. New multiband, two dimensional imaging spectrometer will be developed

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[en] Absolute cross sections for electron-impact single and multiple ionization of Se²⁺ ions were measured using the dynamic-crossed-beams technique over the energy range from the ionization threshold to 500 eV and compared to direct ionization cross sections predicted by the Lotz semi-empirical formula. The single-ionization cross section appears to be dominated by excitation-autoionization of the 4s and 3d inner subshells. The double-ionization measurements are reasonably well accounted for by the semi-empirical fitting formula of Shevelko et al that includes both direct double ionization of the outer 4p subshell and single ionization of the 3p and 3d subshells followed by autoionization. In addition to direct triple ionization, 3p and 3s ionization followed by double autoionization and excitation of the 3p and 3s subshells followed by triple autoionization likely contribute to the triple ionization cross section. (paper)

[en] Absolute electron-impact single and multiple ionization cross-section measurements for Se³⁺ ions were performed using the dynamic-crossed-beams technique over the energy range from the ionization threshold to 1 keV. The experimental single ionization cross section for Se³⁺ shows evidence of significant contributions of 4s–nl (n ≥ 6) and 3d–nl (n ≥ 4) inner-shell excitation-autoionization. The cross sections for double and triple ionization are dominated by ionization-autoionization and ionization-double autoionization of a 3p or 3s electron, respectively. The measurements were compared with the direct ionization cross sections predicted by the Lotz semi-empirical formula for direct ionization. The maximum values of cross sections for single, double, and triple ionization are compared. (paper)

[en] Absolute cross sections for photoionization and electron-impact ionization of Ar⁵⁺ have been measured using two different interacting-beams setups. The spectra consist of measurements of the yield of products due to single ionization as a function of electron or photon energy. In addition, absolute photoionization and electron-impact ionization cross sections were measured to normalize the measured Ar⁶⁺ product-ion yield spectra. In the energy range from 90 to 111 eV, both electron-impact ionization and photoionization of Ar⁵⁺ are dominated by indirect 3s subshell excitation-autoionization. In the energy range from 270 to 285 eV, resonances due to 2p-3d excitation-autoionization are prominent in the photoionization spectrum. In the range from 225 to 335 eV, an enhancement due to 2p-nl (n>2) excitations are evident in the electron-impact ionization cross section. The electron and photon impact data show some features due to excitation of the same intermediate autoionizing states

[en] Relative cross sections for photoionization of W^q+ ions q = 1, ..., 5 were measured at energies up to 90 eV employing the photon-ion merged-beam technique at the Advanced Light Source in Berkeley. While the cross sections for the lower charge states are dominated by broad resonance features in the range of 4f and 5p excitations, the cross section for W⁵⁺ shows much narrower peak features.

[en] Absolute cross sections were measured for photoionization of Ce^q+ (1 ≤ q ≤ 9) ions at photon energies between 110 eV and 150 eV with a spectral resolution of 0.1 eV. The cross sections in this energy range are dominated by 4d - nf and 4d - np autoionizing transitions. Within the experimental uncertainty, total oscillator strengths for the 4d shell determined by integrating the cross-section measurements are consistent with the sum rule value of 10 based on the number of 4d electrons.

[en] Absolute single photoionization cross-section measurements of Se³⁺ and Se⁵⁺ ions were performed using monochromatized synchrotron radiation and the photo-ion merged-beams technique. Se³⁺ measurements were made at a photon energy resolution of 20 ± 3 meV from 41.90 to 54.56 eV, spanning the ²P_1/2 ground state ionization threshold. Numerous autoionizing resonances arising from both the ²P_1/2 ground state and ²P_3/2 metastable state are identified using quantum defect analysis. For Se⁵⁺, measurements were made at a photon energy resolution of 60 ± 10 meV from 81 to 101 eV, spanning the ²S_1/2 ground state ionization threshold, and at a photon energy resolution of 28 ± 3 meV from 100.175 to 106.675 eV in a region rich with autoionizing resonances. The direct ionization threshold of the Se⁵⁺²S_1/2 ground state is experimentally determined to be 81.780 ± 0.010 eV. (paper)

[en] Absolute photoionization cross-section measurements are reported for Se⁺ in the photon energy range 18.0-31.0 eV, which spans the ionization thresholds of the ⁴S_3/2 ground state and the low-lying ²P_3/2,1/2 and ²D_5/2,3/2 metastable states. The measurements were performed using the Advanced Light Source synchrotron radiation facility. Strong photoexcitation-autoionization resonances due to 4p → nd transitions are seen in the cross-section spectrum and identified with a quantum-defect analysis.