Interaction of atomic ions with electrons : Recombination rate coefficients for C1+, F5+, Ne5+, S14+,S15+

Abstract: 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.