Shinobu Nakazaki

Electron-impact cross sections and rate coefficients for excitations of carbon and oxygen ions

Abstract Cross sections have been compiled for electron-impact excitation of carbon and oxygen ions (C II–VI and O II–VIII). A selection has been made to recommend “best” values for use. The resulting recommended values are fitted to an analytical formula and the fitting coefficients are given in a table. The cross sections (in the form of collision strengths) and the rate coefficients calculated therefrom are shown graphically. The reliability of the recommended data is roughly estimated.

Recommended data for excitation rate coefficients of helium atoms and helium-like ions by electron impact

Abstract Cross sections or effective collision strengths are compiled for electron-impact excitation of helium atoms and He-like ions. An evaluation is made to identify the “best” determined values for use for the transitions 1 1 S −2 1,3 S and 1 1 S −2 1,3 P of target ions of Z = 2, 3, 6, 8, 12, 20, 22, 26, 28, 34, and 42. The resulting evaluated data are fitted to an analytical formula to generate a set of recommended values. The fitting coefficients are given in a table; the rate coefficients calculated therefrom are shown graphically. The reliability of the recommended data is estimated roughly.

Rate coefficients for electron impact excitation of helium-like ions within the Dirac R-matrix approach

The Dirac R-matrix theory is used to calculate the collision strengths for electron impact excitation of He-like ions (S14+, Ca18+ and Fe24+) using the Dirac atomic R-matrix code, which has been developed mainly by Norrington and Grant (Norrington P H and Grant I P 1987 J. Phys. B: At. Mol. Phys. 20 4869). The lowest 31 target levels are included in the calculation. Rate coefficients are obtained for transitions from the ground 1s2 1S0 state to the fine-structure levels of all excited states of 1s2l (l = 0,1) and 1s3l (l = 0,1,2) configurations. We compare our results for rate coefficients with the results of previous calculations, and indicate where significant differences arise because of our more accurate representation of resonance and relativistic effects.

Study of fast electron transport in hot dense matter using x-ray spectroscopy

Experimental study on energy transport in ultra-high intensity laser plasma was made. X-ray emission from a triple-layer target irradiated at 10 19 W cm -2 was observed with x-ray spectrographs, monochromatic imagers and an x-ray polarimeter to provide a temperature profile in the depth of the target, lateral extension of the heated region and the velocity distribution function of hot electrons. For PW plasma, a very shallow region (∼0.5 μm from the target surface) was heated up to 650eV but the temperature of deeper region (up to 5 μm) was around 100eV. These depths are much shorter than those expected from the classical penetration of the hot electrons. The localized energy deposition is also found for the plasma generated at 10 17 W cm -2 , and the degree of polarization of the helium-like Cl-Heα line (1s 2 1 S 0 -1s2p 1 P 1 ) from the surface region is polarized parallel to the surface direction whereas that from a deeper region is in perpendicular to it. The experimental result is analysed using a two-dimensional Maxwellian distribution function for hot electrons. Beam-like distribution was found in the depth of plasma.

Electron-Exchange Effect in Electron-Impact Excitation of the n=2 Fine-Structure Levels of Hydrogenic Ions

The electron-impact transitions between the n =2 fine-structure levels of hydrogenic ions are calculated by an improved close coupling scheme that accounts for the electron-exchange effect. It is f...

Energy Distribution of Secondary Electrons in Electron-Impact Ionization of Hydrogen-Like Ions

The energy distribution of secondary electrons in electron-impact ionization of ions is important in computer simulation of high temperature plasmas. Surprisingly enough, no one has published the required data. In this paper, the Coulomb-Born type calculations with and without electron-exchange effect are reported. The 1/ Z 4 scaling law holds fairly well down to smaller Z values, Z being the nuclear charge of the hydrogen-like target ion. The dependence on the incident electron energy is represented fairly accurately by an empirical factor in the approximation without electron exchange.

Energy levels and radiative rates for transitions in Ar XIII, Ar XIV and Ar XV

Energies for 524 levels of Ar XIII, 460 levels of Ar XIV and 156 levels of Ar XV have been calculated using the  code of Dyall et al. (1989). Additionally, radiative rates, oscillator strengths, and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Comparisons are made with the limited results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 1%, whereas results for other parameters are probably accurate to better than 20%. Additionally, the level lifetimes derived from our radiative rates are in excellent agreement with measured values.

Excitation of xenon by electron impact

Electron impact excitation of the lowest nine excited levels ( and ) of Xe is studied theoretically. The cross sections, both integral and differential, are calculated up to 35 eV using the Breit - Pauli R-matrix method. At collision energies below 15 eV, all the integral cross sections show resonance structure. At 15 and 20 eV, the resulting differential cross sections are compared with experimental results. The overall agreement is satisfactory.

Ionization cross sections of helium and hydrogenic ions by antiproton impact

The antiproton-impact cross sections are calculated for hydrogenic ions, hydrogen negative ion, and helium at lower collision energies than reported before. The electronic wave function is expanded in terms of the atomic orbitals centered on the target nucleus in a semiclassical common trajectory method, which includes the trajectory bending effect. The absorption potential is used to circumvent an unphysical reflection of electronic continuum wave function during the collision. At low energies, the absorption potential is effective for the neutral target and the trajectory bending effect is important for the ionized target.

Electron-impact excitations between the n = 2 fine-structure levels of hydrogenic ions

The electron-impact transitions of n =2 fine-structure levels in hydrogenic ions are treated employing two kinds of close coupling methods and the Coulomb–Born approximation. By using these methods together, a reduction of calculation labor is attempted. The obtained results considerably differ from those of a previous close coupling calculation by Zygelman and Dalgarno [Phys. Rev. A 35 (1987) 4085] at low energies.