Electron-impact excitation cross sections from the ground state to the individual magnetic sublevels of the excited state $1s2s^{2}2p_{1/2}J=1$ for highly charged berylliumlike ions have been calculated by using a fully relativistic distorted-wave (RDW) method. The degrees of linear polarization of the corresponding radiations are obtained. It is found that the Breit interaction makes the linear polarization of radiations decrease, and this character becomes more evident with increasing of incident electron energy. For a given energy in threshold units, the linear polarization without the Breit interaction included increases very slowly as the atomic number increases, however, the linear polarization with the Breit interaction included decreases rapidly. These characteristics are very different from the conclusions for the linear polarization of the same radiations but formed by the dielectronic recombination process [ Phys. Rev. Lett. 103, 113001 (2009)], in which the Breit interaction makes the linear polarization increase, and the linear polarization with the Breit interaction included increases with increasing of the atomic number.

Cross sections for electron-impact excitation and capture to individual magnetic sublevels of Cu-like to Se-like gold ions have been calculated by using a fully relativistic distorted-wave (RDW) method. These magnetic cross sections have further been used to obtain the degrees of linear polarization for the first two strongest 5f$\rightarrow${}3d radiative lines. A detailed comparison has been made between polarizations of these lines from the electron-impact excitation process and those of the same lines but from the dielectronic recombination process. It is found that for a Cu-like gold ion the polarization in the electron-impact excitation process increases sharply before starting to decrease at higher incident electron energies, and it reaches the maximum at around twice the threshold energy. The situations for other gold ions are very similar. However, as for the dielectronic recombination process, the polarization changes among a very large range with different gold ions. Therefore, the obvious differences between the polarizations from different formation processes can be employed in diagnosing the formation mechanism of the corresponding lines.

The angular distribution of the $K{\alpha }_1$ ($1s2p_{3/2}{}^{1,3}{P}_{1,2}\to 1s^2{}^1{S}_0$) x-ray emission following the radiative electron capture into initially hydrogenlike ions with nonzero nuclear spin has been studied within the density matrix theory and the multiconfiguration Dirac-Fock method. Emphasis is placed especially upon the hyperfine interaction and how this interaction of the magnetic moment of the nucleus with those of the electrons affects the angular properties of the $K{\alpha }_1$ radiation. Calculations were performed for selected isotopes of heliumlike Sn${}^{48+}$, Xe${}^{52+}$, and Tl${}^{79+}$ ions. A quite sizable contribution of the hyperfine interaction upon the $K{\alpha }_1$ angular emission is found for isotopes with nuclear spin $I=1/2$, while its effect is suppressed for (most) isotopes with nuclear spin $I>1/2$. We therefore suggest that accurate measurements of the $K{\alpha }_1$ angular distribution at ion storage rings can be utilized as a tool for determining the nuclear parameters of rare stable and radioactive isotopes with $I\ge 1/2$.

The linear polarization of the characteristic lines $L{\alpha }_1$ $\left(3d_{5/2}\to 2p_{3/2}\right)$ and $L{\alpha }_2$ $(3d_{3/2}\to 2p_{3/2})$, following inner-shell photoionization of neutral tungsten, is analyzed both experimentally and theoretically. In the experiment, a tungsten target is photoionized by the primary emission of an x-ray tube with incident photon energies in the range of 10.2–30 keV. The $\sigma$ and $\pi$ components of the emitted fluorescence are measured by using a spectropolarimeter, based on x-ray diffraction at Bragg angles close to ${45}^{\circ }$. The degree of linear polarization of the $L{\alpha }_1$ and $L{\alpha }_2$ lines is determined to be $+(1.6\pm 0.5)\%$ and $-(7\pm 2)\%$, respectively. In addition, this degree of polarization is calculated within the framework of the density-matrix theory as a function of the incident photon energy. These calculations are in good agreement with the experimental results and show only a weak dependence of the degree of polarization on the energy of the incident photoionizing photon.

Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.

The angular distribution and the photon-photon angular correlation have been investigated for the x-ray emission from two-step radiative cascades that proceed via overlapping intermediate resonances. In particular, density matrix theory is applied in order to explore how the splitting of these intermediate levels affects the subsequent x-ray emission and whether measurements of photon angular distributions may help reveal level crossings in highly charged ions, if analyzed along isoelectronic sequences. Detailed computations within the multiconfiguration Dirac-Fock method were performed especially for the two-step $1s2p^2{J}_i=1/2,3/2\to 1s2s2pJ=1/2,3/2+{\gamma }_1\to 1s^{2}2s{J}_f=1/2+{\gamma }_1+{\gamma }_2$ cascade of lithiumlike ions, for which a level crossing of the two $1s2s2pJ=1/2,3/2$ intermediate resonances occurs in the range $74\le Z\le 79$. For this cascade, a remarkably strong depolarization effect, associated with the finite lifetime of these intermediate levels, is found for the angular distribution and the photon-photon correlation function for all level splittings $\Delta \omega \lesssim 0.2\text{a.u.}\approx 5.4$ eV. We therefore suggest that accurate angle-resolved measurements of the x-ray emission may serve also as a tool for determining small level splittings in excited highly charged ions.