Dielectronic Recombination Of Li-like Ca¹⁷⁺ And F-like Fe¹⁷⁺ Ions At Heavy Ion Storage Ring CSRm

Dielectronic recombination?DR?and Radiative Recombination?RR?are two fundamental electron-ion collision processes in various plasmas.The precision determination of the absolute rate coefficients of electron-ion recombination is demanded to understand the astrophysical and other natural as well as man-made plasmas.Based on the electron-ion recombination spectrometer at the main cooler storage ring?CSRm?at the Institute of Modern Physics in Lanzhou,China,DR experiments of Li-like calcium and F-like iron have been performed,and the RR rates enhancement of several highly charged ions have been investigated.The work in this thesis includes the following two parts.In the first part,DR rate coefficients of Li-like ⁴⁰Ca¹⁷⁺and F-like ⁵⁶Fe¹⁷⁺ions were measured at the storage ring CSRm.For Li-like ⁴⁰Ca¹⁷⁺,the experiment was performed within energy range of 0-42 eV,which covers all the?n=0 DR resonance series of 2s core electron(2s_1/2?2p_1/2 nl and 2s_1/2?2p_3/2 nl).Meanwhile,the transition energy of²S_1/2?²P_1/2/2 and ²S_1/2?²P_3/2 were determined to be 35.95±0.35 eV and 41.05±0.06 eV,respectively.For F-like ⁵⁶Fe¹⁷⁺,the measured energy range was 0-6 eV,several DR resonances associated with the???n=0 transition of 2s² 2p⁵[²P_3/2]nl to 2s² 2p⁵[²P_1/2]nl were observed.For a better understanding of the DR spectra,a theoretical calculation using the FAC code is performed for both ions and compared with experimental results.The calculated data and the experimental results have a good agreement at the high electron-ion collision energies,but have discrepancies in the low energy range,which indicates that theory is unable to calculate precisely the DR rate coefficients in the low energy range.Finally,for both ions,the temperature dependent plasma recombination rate coefficients were derived from the measured and calculated DR rate coefficients by convoluting it with Maxwellian electron energy distribution.The plasma rate coefficients were compared with the theoretical data from the literature.The present results constitute a set of bench-mark data for use in astrophysical plasma modeling.In the second part,the electron-ion recombination spectra for Li-like Ar¹⁵⁺,Be-like Ar¹⁴⁺,Be-like Ca¹⁶⁺and F-like Ni¹⁹⁺have been measured and carefully interpreted in very low energy range.For a better understanding of the spectra,the calculated results with the standard RR and DR theories were compared with the experimental results.In addition to the calculations,we have also fitted the experimental data with flattened Maxwellian function included RR and DR contributions.Large discrepancies have been found at low energy range especially below 10 meV,and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients.For the electron-ion collision energy below 1 meV,it was found that the experimentally observed recombination rates are higher than the theoretically predicted rates and fitted rates by a factor of 1.5 to 3.9.The strong dependence of RR rate coefficients enhancement on the charge states of ions and electron beam temperature has been found,in accordance with the previous enhancement effects found in the low-energy recombination experiments at the heavy ion storage rings.