R. E. H. Clark

Collision strengths and oscillator strengths for excitation to the n = 3 and 4 levels of neon-like ions

Collision strengths are given for the 88 possible fine-structure transitions between the ground level and the n = 3 and 4 levels in 20 neon-like ions with nuclear charge number Z in the range 18 less than or equal toZless than or equal to74. The results are given for the nine impact-electron energies in threshold units X = 1.0, 1.2, 1.5, 1.9, 2.5, 4.0, 6.0, 10.0, and 15.0. In addition, electric dipole oscillator strengths obtained by various methods are given. copyright 1987 Academic Press, Inc.

X-RAY TRANSMISSION CALCULATIONS FOR AN ALUMINUM PLASMA

Computer programs developed recently at Los Alamos have been used to calculate the transmission of x rays through an aluminum plasma. Theoretical energy levels, oscillator strengths, and photoionization cross sections were combined with the local thermodynamic equilibrium population model to calculate the plasma absorption coefficient as a function of photon energy. The transmission spectrum is simulated by accounting for the plasma depth and spectrometer characteristics. These results are compared to spectra observed during recent experiments; excellent agreement is obtained.

Electron-impact collision strengths for excitation of He-like ions from the levels with n=1 and 2 to all singly excited levels with higher n≤5

Intermediate-coupling collision strengths have been calculated for all transitions of the kind 1s2p2s+1PJ-1sn′l′2s′+1L′J′ with n′=3, 4, and 5 and l′≥1 (p, d, f, g) for 20 He-like ions with nuclear charge number Z in the range 4≤Z≤74. The method used is a Coulomb-Born-Exchange method that is especially well suited for calculating results for many members of an isoelectronic sequence simultaneously. The calculations were made for nine impact-electron energies in threshold units e=1.0, 1.2, 1.5, 1.9, 2.5, 4.0, 6.0, 10.0, and 15.0. The results are given in the form of fits to a simple function of e that is readily integrated over a Maxwellian to obtain collision rates. The parameters required in obtaining collision strengths for the simpler transitions from the 1s2p levels to the 1sn′s levels with 3≤n′≤5 and for the transitions from the ground level and the 1s2s levels to all singly excited levels with higher n values ≤5 are given, as well. Results for transitions between energy terms and their jj coupling analogs are also included. In addition, calculated values for the transition energies and the electric-dipole radiative line strengths are given for all transitions.

Collision strengths and line strengths for fine-structure transitions between the 2la2lb configurations and the 2l′a3l′b configurations in Be-like ions☆

Abstract Collision strengths have been calculated for all fine-structure transitions between the levels of the 2la2lb configurations and those of the 2l′a3l′b configurations in 17 Be-like ions with nuclear charge number Z in the range 10 ⩽ Z ⩽ 74 for nine impact-electron energies ϵ in threshold units in the range 1 ⩽ ϵ ⩽ 15. Fits of all the collision strengths to simple functions of ϵ that are readily integrated over a Maxwellian distribution to obtain collision rates are given. Also given are the results for transitions between energy terms. In addition, the electric-dipole radiative line strengths and the transition energies are listed. The method used is a Coulomb-Born-exchange method that is well suited for handling many members of an isoelectronic sequence simultaneously. The calculations include both configuration mixing and intermediate coupling effects.

Isoelectronic sequence fits to configuration-averaged photoionization cross sections and ionization energies

Abstract Hartree-Fock wave functions have been used to calculate configuration-averaged photonization cross sections and ionization energies for orbitals 1 s ⩽ nl ⩽ 5 g in He-like through Al-like isoelectronic sequences. The photoionization cross sections have been fitted as a function of the nuclear charge, Z , and photon energy, X , in threshold units, with average error of less than 10%. The ionization energies have been fitted as a function of Z with errors of less than 0.5%.

Electron beam effects on the spectroscopy of satellite lines in Aluminum X-pinch experiments

Aluminum wire X-pinch experiments performed at the Cornell University XP pulsed power generator show detailed high resolution spectra for satellite lines of Li-like, Be-like, B-like and C-like ions. These lines, which correspond to transitions originating from autoionizing levels, are observed in the direction of the anode with respect to the hot X-pinch cross point. The intensities of such satellites are much smaller or absent in the direction of the cathode. These transitions are caused by collisions of ions with energetic electrons (5-15 keV) which are created by inductance between the hot spot and the anode. A collisional-radiative model was constructed using a non-Maxwellian electron energy distribution consisting of a thermal Maxwellian part plus a Gaussian part to represent the high energy electron beam. The shapes of the observed satellite structures are consistent with the calculated spectrum for electron temperatures between 30-100 eV, and beam densities of about 10−7 times the plasma electron density.

Kinetics calculations for near Ne-like ions

Abstract The purpose of the present work is to systematically test the sensitivity of steady-state kinetics to variations in the atomic modeling for plasmas in a near Ne-like state. The effect of 2 s vacancies autoionizing states, high lying excited states and electron density is studied. In addition, kinetics calculations using configuration average modeling are compared to similar calculations using detailed fine structure levels. Results are presented mainly for the charge state distribution of selenium. However, relative gain coefficients are calculated for both selenium and silver. These calculations predict somewhat larger gains for the J = 2 → 1 lasing transitions than for the 0 → 1 transitions, which agrees with experimental trends.

Electron-impact collision strengths for inner-shell excitation of doubly excited levels from singly excited levels in He-like ions

Abstract A simple Coulomb-Born-Exchange method has been used to calculate electron-impact colision strengths for inner-shell excitation of the doubly excited levels with n = 2 in He-like ions from the singly excited levels. The results are of particular interest for plasma diagnostic purposes. The calculations were made for nine impact electron energies in threshold units ϵ = 1.0, 1.2, 1.5, 1.9, 2.5, 4.0, 6.0, 10.0 and 15.0 for 19 He-like ions with nuclear charge number Z in the range 6 ≤ Z ≤ 74. Fits are given of the scaled collision strength Z 2 Ω to simple functions of ϵ that are readily integrated over a Maxwellian distribution to obtain collision rates. Configuration-interaction and intermediate-coupling effects have been included in the calculations. Calculated values for transition energies and radiative line strengths are also given.

X-ray spectra of multiply-charged hollow ions in the emission from a femtosecond laser plasma

A new type of quasicontinuous emission spectrum from a femtosecond laser plasma near the Lyα line of H-like ions is obtained and interpreted. It is shown that these spectra are emitted by multiply charged hollow ions, which are present in the plasma on account of its ultrahigh density, which, in turn, is due to the use of high-contrast laser pulses for producing the plasma. A new spectroscopic approach based on analysis of the composition of spectral complexes of hollow ions is discussed.

Collision strengths for innershell excitation of Li-like ions from the 1s22s and 1s22p levels to the 1s2l3l′ levels

Abstract Collision strengths, collision rates, transition energies, and electric-dipole radiative line strengths have been calculated for innershell excitation from the 1s22s and 1s22p levels to all levels of the 1s2l3l′ configurations in Li-like ions with nuclear charge number Z in the range 6 ⩽ Z ⩽ 74. The collision strengths, which are obtained using a Coulomb-Born-exchange method, are expressed in a convenient form in terms of the scaled hydrogenic ion collision strengths Z 2 Ω H and Z 2 Ω H e . Results for innershell excitation to the levels of the 1s2l2l′ configurations considered in earlier work are also expressed in this form. The calculations include configuration mixing, parentage mixing, and intermediate coupling effects.