Dielectronic recombination experiment of Na-like Kr<sup>25+</sup> at the heavy ion storage ring CSRe

The experimental study of precision spectroscopy of dielectronic recombination (DR) of highly charged ions is not only important for astronomical plasmas and fusion plasmas, but also can be used as a new precision spectroscopy method to test the strong-field quantum electrodynamic effect, measure isotope shift and extract the radius of atomic nuclei. An specially designed electron beam energy detuning system for electron-ion recombination precision spectroscopy experiments has been installed at the heavy ion storage ring CSRe in Lanzhou, where the electron-ion collision energy under the center-of-mass system can be detuned to 1 keV, and an independently-developed plastic scintillator detector and multiwire proportional chamber detector have been installed downstream of the electron cooler of the CSRe for the detection of recombined ions. The multiwire proportional chamber detector has the ability to non-destructively monitor the profile of the ion beam in real-time while acquiring the recombined ion counts, providing guidance for optimization of the ion beam. On this basis, the first test experiment of dielectronic recombination of Kr²⁵⁺ ions has been carried out at the CSRe, and the dielectronic recombination rate coefficients in the range of 0-70 eV at the frame of center-of-mass were measured. In order to fully understand the experimental results, we calculated the dielectronic recombination rate coefficients of the Kr²⁵⁺ ion using the Flexible Atomic Code (FAC) and made a detailed comparison with the experiment, which is in good agreement, and only the resonance energies of the two resonance peaks at 1.695 eV and 2.573 eV are significantly different. In addition, the DR resonance energies and intensities were obtained by fitting the experimental results in the range 0-35 eV, and we found that the transition 3s→4l (∆n=1) contributes significantly to the experimental spectral lines. Furthermore, we compare the plasma rate coefficients derived from the DR rate coefficients with those derived from the AUTOSTRUCTURE and FAC theories, which differ by 20 percent in the temperature range less than 10⁶ K. The experimental results show that the DR experimental platform of the CSRe has very good stability and reproducibility, and can provide support for the future DR experiments of highly charged ion, i.e. for testing strong-field quantum electrodynamics effect and measuring the properties of atomic nuclei.