This thesis contains results of electron-ion recombination processes in atomic ions relevant for plasma applications. The measurements were performed at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) and at the CRYRING heavy-ion storage ring. Dielectronic recombination (DR) cross sections, resonant strengths, rate coefficients and energy peak positions in H-like and He-like S are obtained for the first time from the EBIT measurements. Furthermore, the experimentally obtained DR resonant strengths are used to check the behaviour of a scaling formula for low Z, H-and He-like iso-electronic sequences and to update the fitting parameters. KLL DR peak positions for initially He- to B-like Ar ions are obtained experimentally from the EBIT measurements. Both the results from highly charged sulfur and argon are compared with the calculations performed with a distorted wave approximation.

Absolute recombination rate coefficients of B-like C, B-like Ne and Be-like F ions are obtained for the first time with high energy resolution from storage ring measurements. The experimental results are compared with the intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients of each of these ions are obtained by convoluting the energy dependent recombination spectra with a Maxwell-Boltzmann energy distribution in the temperature range of 10³-10⁶ K. The resulting plasma rate coefficients are presented and compared with the calculated data available in literature.

This thesis concentrates on electron-ion interaction studies, in particular focusing on dielectronic recombination (DR) of highly charged ions relevant to astrophysics and plasma physics. The measurements were performed at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) and at the CRYRING heavy-ion storage ring. For the R-EBIT measurements a newly developed time-of-flight (TOF) technique for separation of ions and detecting the charge state distribution was utilized. By using ion intensities derived from the TOF spectra as input parameters in the rate equations, energy dependent DR rate coefficients for S¹⁵⁺ and S¹⁴⁺ ions were obtained for the first time. Resonance energies and cross sections calculated within the relativistic many-body perturbation theory for S¹⁵⁺ agree well with the experimental data. In addition to the TOF spectra, the x-ray spectra have been also collected. The combination of these two measurements allows us to separate the photo-recombination and the excitation spectra, from which the excitation rate coefficients for S¹⁵⁺ and S¹⁴⁺ ions were extracted.

From the storage ring measurements absolute recombination rate coefficients for C¹⁺, F⁵⁺, and Ne⁵⁺ions as a function of electron-ion collision energy were obtained. These were reported for the first time with high energy resolution. The experimental results were compared with results obtained from AUTOSTRUCTURE calculations. Temperature dependent rate coefficients have been also derived for the studied ions and compared with calculations available in the literature.