Showing papers by "Hiroyuki A. Sakaue published in 2020"

Collisional-radiative modeling of the 5 p − 5 s spectrum of W xiv –W xvi ions

Abstract: The wavelength and rate of the $5p\ensuremath{-}5s$ transition of W xiv--W xvi ions have been calculated by the relativistic configuration interaction method with the implementation of the flexible atomic code. A reasonable collisional-radiative model has been constructed to simulate the $5p\ensuremath{-}5s$ transition spectrum of W xiv--W xvi ions, which had been observed in the electron beam ion trap device. The results are in reasonable agreement with the available experimental and theoretical data, which might be applied to identify the controversial spectra. The confusion on the assignment of the ionization stage is solved in the present work.

Identification of visible lines from multiply charged W 8 + and W 9 + ions

Abstract: We present an investigation of previously unidentified visible lines for ${\mathrm{W}}^{8+}$ and ${\mathrm{W}}^{9+}$ from the spectra observed using an electron-beam ion trap. The analysis is based on collisional-radiative (CR) modeling with fine-structure sublevel population kinetics. To ensure the identification of lines done by the CR model, we have also performed an accurate calculation of transition energies and transition probabilities within the multiconfigurational Dirac-Fock approach using grasp2018. In the spectrum, most of the observed lines are assigned as magnetic dipole transitions belonging to the first two lower-lying configurations of these ions.

Observation of light and secondary ion emissions from surfaces irradiated with highly charged ions

Abstract: Visible light and secondary ions emitted from various sample surfaces (Si, HOPG, Cu, and Teflon) were observed after irradiation with highly charged ions (HCIs). HCIs were produced using an electron beam ion source (Kobe EBIS) at Kobe University. Visible emissions were detected using a liquid nitrogen cooled CCD detector. The mass spectrum of secondary ions was obtained using a quadrupole mass analyzer. The major constituent in both light and secondary ion emissions was hydrogen. Balmer lines were the dominant form of light emission as observed from spectra, and proton signals were the most intense peaks in SIMS spectra. The emission intensity of Balmer light and the proton signal intensity (as observed from the SIMS spectrum) both increased as the charge state of the incident HCI increased. Both intensities were roughly proportional to the third to fourth power of the charge state. Spatial distribution of Balmer light was measured and the kinetic energy of hydrogen sputtered from the surface was estimated to be ∼20 eV. The SIMS measurement results for the Teflon sample demonstrate the advantage of using SIMS with an HCI probe for detecting electronegative elements.

NIFS Atomic and Molecular Numerical Database for Collision Processes

Abstract: The National Institute for Fusion Science (NIFS) has compiled and developed atomic and molecular numerical databases for various collision processes and makes it accessible from the internet to the public. The database contains numerical data of cross sections and rate coefficients for electron collision or ion collisions with atoms and molecules, attached with bibliographic information on their data sources. The database system provides query forms to search data, and numerical data are retrievable. The graphical output is helpful to understand energy dependence of cross sections and temperature dependence of rate coefficients obtained by various studies. All data are compiled mainly from published literature, and data sources can be tracked by the bibliographic information. We also have data of sputtering yields and back-scattering coefficients for solid surfaces collided by ions in the database. All data in the database are applicable to understand atomic and molecular processes in various plasmas, such as fusion plasma, astrophysical plasma and applied plasma, as well as for understanding plasma–surface interaction in plasmas.