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Interference between radiative and dielectronic recombination in electron and highly charged Bi ion collisions has been studied by observing emitted x-rays with the Tokyo electron beam ion trap. The so-called Fano line shapes were fitted to the KLL DR resonant profiles observed as the enhancement of the x-ray counts. The shape parameters q have been determined similarly to the previous experiments for highly charged U [D A Knapp et al 1995 Phys. Rev. Lett. 74 54] and Hg ions [A J Gonzalez Martinez et al 2005 Phys. Rev. Lett. 94 20320]. The present results were compared to the previous results.

Recent activities at the Tokyo electron beam ion trap related to observations of resonant processes in the collisions of electrons with open-shell highly charged ions are reported. Extracted ion observations and high resolution x-ray spectroscopic observations have been applied to resolve the contribution from different charge states. In particular, dielectronic recombination (DR) of a H-like ion have been observed by high resolution x-ray spectroscopy for the first time. The DR satellite spectra obtained in the present experiment are compared with theoretical spectra.

This paper reports a systematic study of the dependence on atomic number of the dielectronic recombination resonance strengths for He-like, Li-like and Be-like ions. Recent measurements of dielectronic recombination resonance strengths for the KLL and KLM manifolds for iron, yttrium, iodine, holmium, and bismuth are also described. The resonance strengths were normalized to calculated electron impact ionization cross sections. The measured resonance strengths generally agree well with theoretical calculations using the distorted wave approximation. However, KLM resonance strength measurements on high atomic number open-shell ions gave higher values than those suggested by calculations. Using recently measured data, along with existing results, scaling laws have been generated as a function of atomic number for He-like, Li-like, and Be-like ions in the KLL and KLM manifolds.

$KLL$ dielectronic recombination resonances, where a free electron is captured into the $L$ shell and at the same time a $K$ shell electron is excited into the $L$ shell, have been measured for open shell iodine ions by measuring the detected yield of escaping ions of various charge states and modeling the charge balance in an electron beam ion trap. In the modeling, the escape from the trap and multiple charge exchange were considered. Extracted ions were used to measure the charge balance in the trap. The different charge states were clearly separated, which along with the correction for artifacts connected with ion escape and multiple charge exchange made the open shell highly charged ion measurements of this type possible for the first time. From the measured spectra resonant strengths were obtained. The results were $4.27(39)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$, $2.91(26)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$, $2.39(22)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$, $1.49(14)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$ and $7.64(76)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$ for the iodine ions from He-like to C-like, respectively.

We present a clear observation of a resonant contribution to electron impact ionization of Li-like highly charged ions (I{sup 50+}). Li-like ions are the simplest in which resonant-excitation double autoionization (REDA) can occur. REDA was observed by measuring the ratio of the numbers of trapped ions of two neighbring charge states as a function of electron energy under equilibrium conditions using an electron beam ion trap. The resonant strength was determined by normalizing the experimental data to theoretical ionization cross sections at the nonresonant interaction energies. Good agreement was found between the observed and calculated resonant strengths for this observation of REDA in Li-like highly charged ions.