Zhimin Hu

Different approaches to precise wavelength calibration of a flat-field grating spectrometer for laser-produced plasmas

Accurate mathematical models called one-line calibration and parameter fitting are presented for wavelength calibration of a flat-field grating spectrometer. The models precisely establish the relationship between wavelength and pixel position of the detector, since geometry parameters and the grating equation of the spectrometer are taken into account. Compared with the commonly used polynomial fitting, the models presented here provide more reliable calibration results, especially in the extended region away from the calibration points. In addition to the high precision of calibration, the parameter fitting procedure provides a helpful way to obtain the actual parameters of the spectrometer.

Mechanism of dominance of the Breit interaction in dielectronic recombination

The recent theoretical and experimental studies show that the Breit interaction plays a dominant role in the dielectronic recombination for some particular transitions. The detailed mechanism of why the Breit interaction is dominant for such a process is still unknown. In this work, we performed a simulation and decomposed each individual term in the transition matrix level and found that the Breit interaction is dominant when the leading term ( with the larger of r1 and r2) contribution of the two-electron Coulomb interaction is vanished. Based on this mechanism, we explained why the dielectronic capture strength to state is much stronger than the one to as well as why the Breit interaction plays a dominant role in the anisotropic parameters. Furthermore, the present finding may guide us to search some physical processes in which the Breit interaction is dominant by simply analyzing the coupling coefficients for a given isoelectronic sequence.

Two-photon observations of dielectronic recombination processes

We present here coincidence measurements for two K x-rays emitted in the dielectronic recombination process of hydrogen-like krypton. We report the first observation of clear coincidence signals obtained from two Ge detectors placed in such a way that the Tokyo electron beam ion trap was between them. The doubly differential cross section is obtained by normalizing the coincidence counts to the radiative recombination x-ray counts.

Indirect processes in x-ray line emissions of 5f → 3d transitions of highly charged gold ions

We present an experiment for the 5f → 3d transitions of highly charged gold ions with an electron beam ion trap. The indirect process contributions for these transitions were investigated experimentally.

KLL dielectronic recombination resonance strengths in He- to O-like gold ions

We present experimental observation of the dielectronic recombination (DR) in He- to O-like gold ions performed with the Tokyo electron beam ion trap (EBIT). In the experiment, the abundance ratios between adjacent ions in the EBIT have been obtained as a function of electron energy by measuring the number of extracted ions from the EBIT. The DR cross sections are deduced from the degree of the abundance ratio change at the resonance energy. The experimental DR resonance strengths are compared with fully relativistic calculations.

Dielectronic recombination of hydrogen-like krypton

The KLL dielectronic recombination (DR) of hydrogen-like krypton has been studied with the Tokyo electron beam ion trap. The resonant strengths have been determined by normalizing the DR X-ray intensity to the n = 1 radiative recombination X-ray intensity. The experimental result is compared with multi-configuration Dirac-Fock calculations.

Activities at the Tokyo EBIT 2010

In this paper, we present recent activities at the Tokyo EBIT after giving an overview of the present status of the devices. We have been studying dielectronic recombination processes by means of several techniques. In addition to X-ray observations and charge abundance observations, 2-photon observations have been recently used to study DR processes which emit two photons successively (but practically simultaneously). Recent efforts on spectroscopic work are mainly concentrated on Fe and W ions, which are relevant to astrophysical and fusion plasmas. Several spectrometers that can cover a wide range of wavelength, such as visible, EUV, and X-rays, were used for accumulating useful data for plasma diagnostics applications. HCI-surface collision processes were studied using ions extracted through the beam line, that has recently been modified. Very highly charged ions up to Bi81+ were used for studying the effect of huge potential energy.