Tokyo Electron Beam Ion Trap Research Articles

An application of a Si/CdTe Compton camera for the polarization measurement of hard x rays from highly charged heavy ions.

Methods to measure the polarization of x rays from highly charged heavy ions with a significantly higher accuracy than that of the existing technology are needed to explore relativistic and quantum electrodynamics effects, including the Breit interaction. We developed an Electron Beam Ion Trap Compton Camera (EBIT-CC), a new Compton polarimeter with pixelated multi-layer silicon, and cadmium telluride counters. The EBIT-CC detects the three-dimensional position of Compton scattering and photoelectric absorption, and thus, the degree of polarization of incoming x rays can be evaluated. We attached the EBIT-CC on the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) in the University of Electro-Communications. An experiment was performed to evaluate its polarimetric capability through an observation of radiative recombination x rays emitted from highly charged krypton ions, which were generated by the Tokyo-EBIT. The CC of the EBIT-CC was calibrated for the ∼75keV x rays. We developed event reconstruction and selection procedures and applied them to every registered event. As a result, we successfully obtained the polarization degree with an absolute uncertainty of 0.02. This uncertainty is small enough to probe the difference between the zero-frequency approximation and full-frequency-dependent calculation for the Breit interaction, which is expected for dielectronic recombination x rays of highly charged heavy ions.

Visible transitions of highly charged tungsten ions observed with a compact electron beam ion trap

We present visible spectra of highly charged tungsten ions observed with a compact electron beam ion trap (EBIT). Several transition lines previously observed with the Tokyo EBIT (Watanabe et al 2012 Can. J. Phys. 90 497) have been reproducibly observed. By observing the electron energy dependence in detail, the charge state of the ion responsible for those lines is identified.

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.

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.

High resolution extreme ultraviolet spectrometer for an electron beam ion trap

An extreme ultraviolet spectrometer has been developed for spectroscopic studies of highly charged ions with an electron beam ion trap. It has a slit-less configuration with a spherical varied-line-spacing grating that provides a flat focal plane for grazing incidence light. Alternative use of two different gratings enables us to cover the wavelength range 1-25 nm. Test observations with the Tokyo electron beam ion trap demonstrate the high performance of the present spectrometer such as a resolving power of above 1000.

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.

Structure and dynamics of highly charged heavy ions studied with the electron beam ion trap in Tokyo

In this paper, we present the structure and the dynamics of highly charged heavy ions studied through dielectronic recombination (DR) observations performed with the Tokyo electron beam ion trap. By measuring the energy dependence of the ion abundance ratio in the trap at equilibrium, we have observed DR processes for open shell systems very clearly. Remarkable relativistic effects due to the generalized Breit interaction have been clearly shown in DR for highly charged heavy ions. We also present the first result for the coincidence measurement of two photons emitted from a single DR event.

Electron density dependence of intensity ratio for FeXXII extreme ultraviolet emission lines arising from different ground levels in electron beam ion trap and large helical device

Extreme ultraviolet (EUV) spectra of highly charged iron ions in a wavelength range of 100–300 Å have been observed from two different plasma sources of the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) with a monoenergetic electron beam and a Large Helical Device (LHD) with Maxwellian electron energy. The excitation process of the spectral lines is compared between the two plasmas, and it is found that the excitation process for Fe XIX - Fe XXII ions is clearly different. Namely, the EUV emission lines from the EBIT plasma are only dominated by electron impact excitation connected to the ground state, but the excitation mechanism is not so simple in the LHD plasma. The difference in the excitation process is studied by measuring the intensity ratio of EUV emission lines (114.412 Å [1s22s2p2 2P3/2 → 1s22s22p 2P3/2]/117.144 Å [1s22s2p2 2P1/2 → 1s22s22p 2P1/2]) arising from different ground levels in the Fe XXII ions. The line intensity ratio has an extremely small value of 0.2 in the EBIT plasma with a low beam current of 30 mA and a beam energy of 2 keV, while the ratio varies with the electron density ne in the LHD plasmas, i.e., 0.35 for ne = 1 × 1013 cm−3 and 0.65 for ne = 4 × 1013 cm−3. Here, the electron density of the EBIT plasma is estimated to be smaller than 1012 cm−3 and the electron temperature of the LHD plasmas is 2 keV. The dependence of the line intensity ratio on the observed electron density is analyzed for both the EBIT and the LHD plasmas using several collisional-radiative (CR) models. The present experimental data can easily be reproduced by the analysis when the thermal proton impact excitation is taken into account. The importance of the proton impact excitation is also experimentally verified by injecting an iron pellet into the LHD plasmas and changing the ratio of the proton density to the electron density.

Characterization and parametrization in terms of atomic number of x-ray emission fromK-shell filling during ion-surface interactions

When highly charged ions are incident on a surface, part of their potential energy is emitted as characteristic radiation. The energies and yields of these characteristic x rays have been measured for a series of elements at the Tokyo electron-beam ion trap. These data have been used to develop a simple model of the relaxation of the hollow atoms which are formed as the ion approaches the surface, as well as a set of semiempirical scaling laws, which allow for the ready calculation of the K-shell x-ray spectrum which would be produced by an arbitrary slow bare or hydrogenlike ion on a surface. These semiempirical scaling laws can be used to assess the merit of highly charged ion fluorescence x-ray generation in a wide range of applications.

Measurement of the energy of the (2s1/22p1/222p3/22)5/2–(2s22p1/222p3/2)3/2 x-ray transition in the N-like 208Pb75+

The (2s1/22p1/222p3/22)5/2–(2s22p1/222p3/2)3/2 x-ray transition in the N-like 208Pb75+was observed using the Tokyo electron beam ion trap at the University of Electro-Communications. The Pb spectral line energies were measured relative to the Lyman-α lines of the H-like S and the 1s4p 1P1–1s2 1S0 transition in the He-like P. In the present work, the line from the N-like lead ions is analysed and the transition energy is determined to be 2662.98 ± 0.12 eV. We also calculate the transition energies of the (2s1/22p1/222p3/22)5/2–(2s22p1/222p3/2)3/2 lines in N-like ions from Sn (Z = 50) through U (Z = 92) with the general relativistic atomic structure package Vanderbilt University (GRASPVU) package which is based on the multiconfiguration Dirac–Fock (MCDF) method. The calculations are compared with the available experimental results.

Measurement of the QED energy shift in the1s22p3∕2–1s22s1∕2x-ray transition in Li-likePb79+208

The $1{s}^{2}2{p}_{3∕2}--1{s}^{2}2{s}_{1∕2}$ x-ray transition in the Li-like ${\mathrm{Pb}}^{79+}$ has been observed using the Tokyo electron beam ion trap at the University of Electro-Communications. The contribution of QED $(\ensuremath{-}24.99\ifmmode\pm\else\textpm\fi{}0.10\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ to the $1{s}^{2}2{p}_{3∕2}--1{s}^{2}2{s}_{1∕2}$ transition in $^{208}\mathrm{Pb}^{79+}$ is determined and compared with different calculations. The measurement was made by calibrating the Pb line using the Lyman-$\ensuremath{\alpha}$ lines of the H-like $S$ and the $1s4p\phantom{\rule{0.2em}{0ex}}^{1}P_{1}--1{s}^{2}\phantom{\rule{0.2em}{0ex}}^{1}S_{0}$ transition in the He-like $P$.

Branching ratios of x-ray photons from dielectronic recombination processes in H-like titanium ions

In dielectronic recombination of hydrogenlike ions an intermediate doubly excited heliumlike ion is formed. Since the $K$ shell is empty, both excited electrons can decay sequentially to the ground state. In this paper we analyze the x-ray radiation emitted from doubly and singly excited heliumlike titanium ions produced inside the Tokyo electron beam ion trap. Theoretical population densities of the singly excited states after the first transition and the transition probabilities of these states into the ground state were also calculated. This allowed theoretical branching ratios to be determined for each manifold. These branching ratios are compared to the experimentally obtained x-ray distribution by fitting across the relevant peak using a convolution of the theoretically obtained resonance strengths and energies. By taking into account $2E1$ transitions which are not observed in the experiment, the measured and calculated ratios agree well. This method provides a valuable insight into the transition dynamics of excited highly charged ions.

Recent activities at the Tokyo EBIT 2006

The electron beam ion trap (EBIT) in Tokyo was constructed about 10 years after the first EBIT at Lawrence Livermore National Laboratory was built, and has been being stably operated since then. In this paper, we present recent experimental activities at the Tokyo EBIT. In particular, experiments utilizing slow, very highly charged ion beams extracted from the EBIT are reported. PACS Nos.: 39.10.+j, 32.30.Rj, 34.50.Dy, 34.80.Kw

Interference between dielectronic and radiative recombination in electron - highly charged Bi collisions

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.

Resonant electron processes with open-shell highly charged ion targets

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.

Production and Extraction of Highly Charged Ions from the Tokyo EBIT

In the course of an experimental study on collisional processes of highly charged ions (HCIs), we developed a procedure to produce and extract HCIs with a very high charge-state for various kinds of heavy elements at the Tokyo EBIT (Electron Beam Ion Trap). The charge-state spectra of the extracted HCIs for some elements were measured using dierent EBIT operation conditions.

The 1sLamb Shift in Hydrogenlike Rhodium Measured with an Electron Beam Ion Trap

The 1 s Lamb shift in hydrogenlike rhodium has been measured by observing radiative recombination into the 1 s vacancy of bare rhodium produced and trapped in the Tokyo electron beam ion trap. The ...

X-ray spectroscopy of high-Z highly charged ions with the Tokyo EBIT

We have been using the Tokyo electron beam ion trap to investigate the relativistic and the quantum electrodynamical effects on the atomic structure of few electron heavy ions. In this paper, we present 1s binding energy measurement for hydrogen-like rhodium which was performed as one of such systematic studies. It has been obtained by measuring the X-ray transition energy for radiative recombination into the 1s vacancy of bare rhodium and subtracting the electron beam energy from it. For further investigation, a bent crystal spectrometer for hard X-rays is being developed. The design of the new spectrometer and the preliminary result with it are also presented.

Dielectronic recombination in highly charged He-like ions

We have determined resonant strengths of the KLn (2⩽n⩽5) resonances for helium-like Ti ions and (3⩽n⩽5) resonances for helium-like Fe ions. The results were obtained using the Tokyo electron beam ion trap. Characteristic X-rays from both dielectronic recombination and radiative recombination were detected as the electron beam energy was scanned through the resonances.

Thomson scattering system at the Tokyo electron beam ion trap

A Thomson scattering system has been installed at the Tokyo electron beam ion trap for probing characteristics of the electron beam. A YVO4 green laser beam was injected antiparallel to the electron beam. The image of the Thomson scattering light from the electron beam has been observed using a charged-coupled device camera. By using a combination of interference filters, the spectral distribution of the Thomson scattering light has been measured. The Doppler shift observed for the scattered light is consistent with the beam energy. The beam radius dependence was investigated as a function of the beam energy, the beam current, and the magnetic field at the trap region. The variation of the measured beam radius against the beam current and the magnetic field were similar to those in Herrmann’s prediction. The beam radius as a function of the beam energy was also similar to Herrmann’s prediction but seemed to become larger at low energy.