Table of contents

We use the coherent state path integral and a fermion model for the spin to solve a non-linear bosonic generalization of the Jaynes-Cummings model. The propagators are given explicitly as perturbation series. These are summed up exactly for special cases and the corresponding atomic population inversion as well as energy spectrum and wave functions are deduced.

The signal to noise ratio in hyperfine spectra split by nuclear quadrupole interactions can be improved significantly by cross correlating experimental with theoretical spectra, especially for higher spins. In part I of the paper we present all technical details of this new approach and give examples for half integer and integer spins. In part II we elucidate the difficulties which arise in the attempt to reconstruct distribution functions of the largest component of the electric field gradient tensor V_zz and the asymmetry parameter η from experimental line positions and profiles.

We present a detailed analysis of the spectrum of satellite transitions to the n = 23 and n = 2–4 Ne-like yttrium resonance lines. Satellite lines from the double excited 2s²2p⁵3l3l', 2s²2p⁵3l4l', 2s2p⁶3l3l' and 2s2p⁶3l4l' levels of Na-like Y as well as from 2s²2p⁵3l3l'3l" and 2s2p⁶3l3l'3l" levels of Mg-like Y were observed in spectra from a laser-produced plasma. The x-ray spectra were recorded with high spectral resolution λ/Δλ ≈ 3500–5000 in the wavelength region of the n = 2–3 Ne-like resonance lines and with λ/Δλ > 1000 in the region of the n = 2–4 Ne-like resonance lines. A total of more than 50 spectral features were identified, and their wavelengths were measured. A simple intensity model was developed, which agreed well with the measured spectra and assisted the line identification. The consistency of the model for different spectral regions demonstrates the potential of the Na-like and Mg-like satellite lines for diagnosing plasma conditions.

A multichannel theory, based upon the R-matrix method for electron-atom collisions, is employed in the present work to evaluate the continuous free-free absorption coefficient for the negative ion of lithium. The calculation is performed over a wide range of radiation wavelengths λ = 9113–151 890 Å and temperatures T = 1400–10 080 (K). Significant differences are found to occur when the present results are compared with a previous theoretical evaluation.

Absolute energies of the autoionization states 1s2s²2pⁿ [LSJ] with n = 0–2, 1s2s2pⁿ [LSJ] with n = 1–3 and 1s2pⁿ [LSJ] with n = 2–4 and non-autoionizing states 1s²2s²2pⁿ [LSJ] with n = 0–1, 1s²2s2pⁿ [LSJ] with n = 0–2 and 1s²2pⁿ [LSJ] with n = 1–3 were calculated for ions with nuclear charge Z = 6–54 by using the 1/Z perturbation theory method. Relativistic corrections were taken into account in the frame of the Breit operators. The autoionization rates for the above-mentioned autoionization states for ions with Z = 6–54 were computed as well. These data are very important for modelling the satellite spectra produced by high-temperature plasma with thermal and non-thermal electrons.

Absolute electron-scattering total cross sections for noble gas atoms (He, Ne, Ar, Kr, and Xe) and H₂, N₂, CO, NO, and O₂ molecules have been measured at impact energies between 0.5 and 250 eV by the linear transmission method with the same experimental set-up for all the investigated targets. Generally, our total cross sections have been found to be in good agreement with other data with respect to shape. Some systematic discrepancies in magnitude still exist between results of different groups, especially at the lowest applied energies and in the energy range where the cross sections peak. At these energies, new measurements should be carried out before establishing a reference set of data.

The electric quadrupole (E2) and magnetic dipole (M1) transitions between the levels of the 1s²2s²2p², 1s²2s2p³ and 1s²2p⁴ configurations have been investigated in the carbon isoelectronic sequence. The stationary second-order many-body perturbation theory (MBPT) was used to account for electron correlations. Relativistic corrections were included within the Breit-Pauli approximation. The E2 and M1 transition energies, line strengths and transition probabilities obtained in various approximations are compared with experimental values as well as with results of other theoretical calculations.

The problem of heat flux at the critical surfaces and the surfaces of a pellet of deuterium and tritium (conduction zone) heated by laser have been considered. Ion-electron collisions are only allowed for: i.e. the linear transport equation is used to describe the problem with boundary conditions. The maximum-entropy approach is used to calculate the electron density and temperature across the conduction zone as well as the heat flux. Numerical results are given and compared with those of Rouse and Williams and El-Wakil et al.

The theoretical description of the propagation of an ultrashort pulse in a dispersive and dissipative medium, e.g. a plasma, in the presence of a magnetic field is performed in the space-time domain using a Green's function approach. For the purpose a model equation is constructed in which the source term is represented by a δ-function in space and time. The model equation, which is of the Klein-Gordon type can be given an explicit solution directly in the form of a δ-function part and a wake-field part, for which the argument of a Bessel function contains all the parameters of the problem. The results thus reveal the influence of the Green's function of the plasma frequency, the gyro-magnetic frequency and the damping rate. The resulting Green's function can then be used to derive the plasma response of an ultrashort pulse of arbitrary shape and structure by direct integration of the product of the Green's function and the initial pulse over the spatial source domain. The results should be of interest for diagnostics of plasmas and other media with dispersive and dissipative properties.

An interpolation formula between the energies of a quantum dot in high-and low-magnetic field limits is proposed. The formula is implemented to produce the energy spectra of the parabolic quantum dot in the presence of a magnetic field of arbitrary strength. The transitions in the angular momenta of the ground state energy of interacting electrons confined in the quantum dot as a function of magnetic field strength is studied. A good agreement is obtained when our results are tested against exact numerical work.

We re-examine the theory of collective scattering, bremsstrahlung and the transport of radiation in the solar interior, including the effects of transition-bremsstrahlung, stimulated scattering, relativistic corrections and frequency diffusion during radiative transport, which transforms the transport equation into a differential equation (in frequency) for the radiative flux. When this is taken into account the transport equation can no longer be converted into the equation of "radiative transfer" where the total flux of radiation integrated over all frequencies is related to the temperature gradient via the Rosseland mean opacity. The concept of radiative opacity can only be introduced if the frequency diffusion is ignored or treated as a perturbation. In this case the change in the radiative opacity due to these effects is discussed in view of its importance for the neutrino production rate in the solar interior and compared with previous calculations.