A compact electron beam ion trap (EBIT) has been constructed for spectroscopic studies of moderate charge state ions. The electron beam energy range of the present EBIT is 100–1000eV, for which it is rather difficult to operate an ordinary EBIT which used to be designed for operation with higher electron energy (∼10keV or more). To cut down the running costs, a superconducting wire with a high critical temperature is used for the central magnet so that it can be operated without liquid helium. The performance of the compact EBIT has been investigated through visible spectroscopy of highly charged krypton and iron ions.

Interaction of highly charged heavy ions with electrons is one of the most important atomic processes in high temperature plasmas, including astrophysical plasmas such as solar corona and artificial plasmas such as fusion reactor plasmas. Therefore it has been well studied to date, both theoretically and experimentally, to accumulate the atomic data required for understanding or controlling such plasmas. However, there still remains interesting subjects that receive remarkable attention from the atomic physics point of view. One of them, which is the subject of this review, is substantially large Breit interaction effects on the resonance recombination process called dielectronic recombination. The Breit interaction is a relativistic effect in the electron–electron interaction potential; it is thus generally important for highly charged heavy ions. However, in the calculation of the energy levels for heavy ions, the Breit interaction is still a small perturbation compared with the main Coulomb term. On the other hand for the dielectronic recombination, it was found that the Breit interaction can enhance the cross sections significantly. It was also found that the Breit interaction can play not only an important, but even a dominant role in determining the angular distribution of x-rays emitted in the recombination processes. This topical review introduces the recent experimental and theoretical activities to clarify the essential origin of the strong effects.

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Plasma diagnostics in magnetic confinement fusion plasmas by using visible spectrum strongly depends on the knowledge of fundamental atomic properties. A detailed collisional-radiative model of W$^{26+}$ ions has been constructed by considering radiative and electron excitation processes, in which the necessary atomic data had been calculated by relativistic configuration interaction method with the implementation of Flexible Atomic Code. The visible spectrum observed at an electron beam ion trap (EBIT) in Shanghai in the range of 332 nm to 392 nm was reproduced by present calculations. Some transition pairs of which the intensity ratio are sensitive to the electron density were selected as potential candidate of plasma diagnostics. Their electron density dependence are theoretically evaluated for the cases of EBIT plasmas and magnetic confinement fusion plasmas