Izumi Murakami

EUV spectroscopy of highly charged high Z ions in the Large Helical Device plasmas

We present recent results on the extreme ultraviolet (EUV) spectroscopy of highly charged high Z ions in plasmas produced in the Large Helical Device (LHD) at the National Institute for Fusion Science. Tungsten, bismuth and lanthanide elements have recently been studied in the LHD in terms of their importance in fusion research and EUV light source development. In relatively low temperature plasmas, quasicontinuum emissions from open 4d or 4f subshell ions are predominant in the EUV region, while the spectra tend to be dominated by discrete lines from open 4s or 4p subshell ions in higher temperature plasmas. Comparative analyses using theoretical calculations and charge-separated spectra observed in an electron beam ion trap have been performed to achieve better agreement with the spectra measured in the LHD. As a result, databases on Z dependence of EUV spectra in plasmas have been widely extended.

Temperature dependent EUV spectra of Gd, Tb and Dy ions observed in the Large Helical Device

We have observed a number of different types of extreme ultraviolet (EUV) spectra from highly charged gadolinium (Gd), terbium (Tb) and dysprosium (Dy) ions in optically thin plasmas produced in the Large Helical Device at the National Institute for Fusion Science. Temporal changes in EUV spectra in the 6–9 nm region subsequent to the injections of solid pellets were measured by a grazing incidence spectrometer. The spectra rapidly change from discrete features into unresolved transition arrays (UTAs) following a drop in the electron temperature after the heating power is reduced. In particular, extremely narrowed UTA features, which comprise spectral lines of Ag-like, Pd-like and neighboring ion stages, are observed when the peak electron temperature is less than 0.45 keV due to the formation of hollow plasmas. Some discrete spectral lines of Cu-like and Ag-like ions have been identified in the high and low temperature plasmas, respectively, some of which are experimentally identified for the first time.

Atomic data for dielectronic recombination into C-like oxygen

Energy levels, radiative transition probabilities and autoionization rates for C-like oxygen (O2+) including 1s22s22pnl, 1s22s2p2nl and 1s22p3nl (n = 2–8, l ≤ n − 1) states are calculated by the Hartree–Fock relativistic method (Cowan code). Autoionizing levels above the thresholds 1s22s22p 2P, 1s22s2p2 4P, 2D, 2S, 2P and 1s22p3 4S, 2D are considered. Configuration mixing 2s22pnl + 2p3nl plays an important role for all atomic characteristics. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are presented for the excited 218 odd-parity and 218 even-parity states. The DR rate coefficients are calculated including 1s22s22pnl, 1s22s2p2nl and 1s22p3nl (n = 2–8, l ≤ n −1) states. Contributions from the excited states with n ≥ 8 are estimated by extrapolation of all atomic characteristics to derive the total DR rate coefficient. It is found that the orbital angular momentum quantum number l distribution of the rate coefficients shows a peak at l = 4. The total DR rate coefficient is derived as a function of electron temperature. The state-selective DR rate coefficients to excited states of C-like oxygen, which are useful for modelling O III spectral lines in a recombining plasma, are calculated as well.

Total, Partial, and Differential Ionization Cross Sections in Proton–Hydrogen Atom Collisions in the Energy Region of 0.1–10 keV/u

Single-differential, partial, and total ionization cross sections for the proton–hydrogen atom collision system in the energy region of 0.1–10 keV/u are determined by using the molecular-orbital close-coupling method within a semiclassical formalism. The present cross sections are in an excellent agreement with the recent experiments of Shah et al. [J. Phys. B. 31, L757 (1998)], but decrease more rapidly than the cross sections measured by Pieksma et al. [Phys. Rev. Lett. 73, 46 (1994)] with decreasing energy. The numerical data for all calculated cross sections are included in this paper. A critical evaluation of the existing data for the ionization process in the keV energy range is performed both for the experiment and theory. The recommended data are obtained from a converged close-coupling expansion, which in total includes 362 bound and continuum channels with their wave functions augmented by the electron translation factor in order to insure the correct scattering boundary condition.

Spectral evolution of soft x-ray emission from optically thin, high electron temperature platinum plasmas

The soft x-ray spectra of heavy element plasmas are frequently dominated by unresolved transition array (UTA) emission. We describe the spectral evolution of an intense UTA under optically thin conditions in platinum plasmas. The UTA was observed to have a peak wavelength around 4.6 nm at line-of-sight averaged electron temperatures less than 1.4 keV at electron densities of (2.5–7.5) × 1013 cm−3. The UTA spectral structure was due to emission from 4d–4f transitions in highly charged ions with average charge states of q = 20–40. A numerical simulation successfully reproduced the observed spectral behavior.

Theoretical spectral analysis of extreme ultraviolet emissions from lanthanide atomic ions in plasmas

The extreme ultraviolet emission spectra have been studied theoretically for gadolinium (Gd) and neodymium (Nd) atomic ions in the large helical device at National Institute for Fusion Science, Japan. The spectra have been analyzed and compared with the presently carried out atomic structure calculations using a group of computer codes GRASP92 and RATIP. The complex spectra from the unresolved transition array are generated theoretically. The theory has simulated well the experimental spectra.

Database and Related Activities in Japan

We have constructed and made available atomic and molecular (AM) numerical databases on collision processes such as electron‐impact excitation and ionization, recombination and charge transfer of atoms and molecules relevant for plasma physics, fusion research, astrophysics, applied‐science plasma, and other related areas. The retrievable data is freely accessible via the internet. We also work on atomic data evaluation and constructing collisional‐radiative models for spectroscopic plasma diagnostics. Recently we have worked on Fe ions and W ions theoretically and experimentally. The atomic data and collisional‐radiative models for these ions are examined and applied to laboratory plasmas. A visible M1 transition of W26+ ion is identified at 389.41 nm by EBIT experiments and theoretical calculations. We have small non‐retrievable databases in addition to our main database. Recently we evaluated photo‐absorption cross sections for 9 atoms and 23 molecules and we present them as a new database. We establis...

Extreme ultraviolet spectra of multiply charged tungsten ions

We present extreme ultraviolet spectra of multiply charged tungsten ions observed with an electron beam ion trap. The observed spectra are compared with previous experimental results and theoretical spectra obtained with a collisional radiative model.

Theoretical study on the soft X-ray spectra of E1 transition of W LV ion

Jiaoxia Yang∗, Xiaobin Ding∗1, Rui Sun∗, Fumihiro Koike†, Izumi Murakami‡, Daiji Kato‡, Hiroyuki A Sakaue‡, Nobuyuki Nakamura §, Chenzhong Dong∗ ∗ Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China † Department of physics, Sophia University, Tokyo 102-8554, Japan ‡ National Institute for Fusion Science, Toki, Gifu 509-5292, Japan § Institute for Laser Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan Synopsis A collisional-radiative model was constructed to investigate the spectra of W LV ion from EBIT. A good agreement with previous experiment was obtained and some new transition lines were predicted. The research on the energy level structure and radiation properties of various Tungsten(W) ions was largely spurred by the decision of chosen tungsten as the armor material of ITER divertor due to its favourable properties. In order to monitor and control the tungsten ion impurities produced when the plasma interact with the divertor, the throughout knowledge of the tungsten ions especially the radiation properties are necessary.

Spectra of highly charged Fe ions excited by electron collisions: Dependence on electron energy and density

We present the extreme ultraviolet to soft X-ray spectra of highly charged iron ions observed with an electron beam ion trap (EBIT). An EBIT represents a simple plasma which consists of a quasi-monoenergetic electron beam and trapped ions; it is thus useful for testing the atomic models used in the spectroscopic diagnostics of astrophysical plasmas. The dependence on electron energy and density is compared with model calculations.