Shanghai Electron Beam Ion Trap Research Articles

Experimental and theoretical investigations of visible spectra of W12+

To provide relevant atomic data for fusion research, a collisional-radiative model (CRM) simulation is conducted using the Flexible Atomic Code (FAC) to identify the 10 visible lines for W12+ measured with a compact electron-beam ion trap (EBIT) [Kobayashi et al., Phys Rev A 2015;92:022510]. To search for one missing strong visible line predicted from the CRM results, additional experiments are performed using EBIT devices at the Shanghai EBIT Laboratory. Also, large-scale calculations are performed using the FAC and GRASP codes to check the line identifications and investigate electron-correlation effects for W12+. The excitation energies for the 50 lowest levels arising from 4f145s2, 4f135s25p and 4f125s25p2 of W12+ are presented for the first time, with an average deviation of ∼800 cm−1. The resulting theoretical wavelengths agree well with the experimental values (with an average deviation of ∼1.5%) except for one 540.5 nm line, which calls for further theoretical studies.

Measurement and identification of visible lines from W10+

We present the first measurements of visible radiation from W10+. The ions are produced and confined in an electron-beam ion trap (EBIT) at Shanghai EBIT Laboratory, and the spectra are recorded with a Czerny-Turner spectrometer in the wavelength range 300–700 nm. The observed five new spectral lines are identified using detailed collisional-radiative (CR) modeling of the EBIT spectra. In addition, we perform large-scale theoretical calculations for the lowest 50 energy levels of W10+ using FAC and GRASP codes. The excitation energies obtained by the two independent calculations fit well with each other, with ~0.5% difference on average, and the resulting values are adopted to check our line identifications, with wavelength deviations from experimental results ~1.5% on average.

Observation of indirect ionization of W7+ in an electron-beam ion-trap plasma

In this work, visible and extreme ultraviolet spectra of W7+ are measured using the high-temperature superconducting electron-beam ion trap (EBIT) at the Shanghai EBIT Laboratory under extremely low-energy conditions (lower than the nominal electron-beam energy of 130 eV). The relevant atomic structure is calculated using the flexible atomic code package based on the relativistic configuration interaction method. The GRASP2K code, in the framework of the multiconfiguration Dirac-Hartree-Fock method, is employed as well for calculating the wavelength of the M1 transition in the ground configuration of W7+. A line from the W7+ ions is observed at a little higher electron-beam energy than the ionization potential for W4+, making this line appear to be from W5+. A hypothesis for the charge-state evolution of W7+ is proposed based on our experimental and theoretical results; that is, the occurrence of W7+ ions results from indirect ionization caused by stepwise excitation between some metastable states of lower-charge-state W ions, at the nominal electron-beam energy of 59 eV.

K-shell excitation dielectronic recombination resonance strengths of highly charged He-like to O-like Xe ions

Dielectronic recombination is an important process in high temperature plasmas. In the present work, the KLn (n = L, M, N and O) DR resonance strengths of He-like to O-like xenon ions are measured at the Shanghai electron beam ion trap using a fast electron beam energy scanning method. The experiment uncertainty reaches about 6% with significant improvement of statistics. A relativistic configuration interaction calculation is also made. Theoretical results agree with the experiment results within 15% in most cases.

Photorecombination studies of highly charged tungsten ions at Shanghai EBIT

In this paper, we report studies on photorecombination (PR) processes for highly charged W ions. The experiment was performed at Shanghai electron beam ion trap by employing a fast electron beam-energy scanning technique. The KLL dielectronic recombination (DR) resonance strengths for He- up to O-like W ions were determined. The strong interference effect between DR and radiative recombination (RR) was observed and the Fano factor, which measures the interference degree, was determined for the main resonances of ground state He-, Be-, B-, C-, N-, and O-like W ions. In addition, we show experimentally that an autoionizing state can have both Fano and Lorentzian behavior naturally, depending on the processes involved. A fully relativistic configuration interaction method implemented in the flexible atomic code was employed to calculate DR, RR processes and also the inference effect.

Characteristics of the Shanghai high-temperature superconducting electron-beam ion trap and studies of the space-charge effect under ultralow-energy operating conditions

A high-temperature superconducting electron-beam ion trap (EBIT) has been set up at the Shanghai EBIT Laboratory for spectroscopic studies of low-charge-state ions. In the study reported here, beam trajectory simulations are implemented in order to provide guidance for the operation of this EBIT under ultralow-energy conditions, which has been successfully achieved with a full-transmission electron-beam current of 1–8.7 mA at a nominal electron energy of 30–120 eV. The space-charge effect is studied through both simulations and experiments. A modified iterative formula is proposed to estimate the space-charge potential of the electrons and shows very good agreement with the simulation results. In addition, space-charge compensation by trapped ions is found in extreme ultraviolet spectroscopic measurements of carbon ions and is studied through simulation of ion behavior in the EBIT. Based on the simulation results, the ion-cloud radius, ion density, and electron–ion overlap are obtained.

KLL dielectronic recombination resonant strengths of He-like up to O-like tungsten ions

Dielectronic recombination (DR) is an important process in hot plasma physics as well as in atomic structure and collision theory. This work reports the studies of the KLL DR resonance strengths of He-, Li-, Be-, B-, C-, N-, and O-like tungsten ions, through both experiment and calculation. The experimental resonance strengths were determined within uncertainty below 11% at the Shanghai electron beam ion trap by employing a fast electron beam-energy scanning technique. A fully relativistic configuration interaction method implemented in the flexible atomic code was employed to calculate DR process and also radiative recombination (RR). The consideration of the interference effect between DR and RR was revealed to be necessary to determine the resonance strength.

Quantum interference between resonant and nonresonant photorecombination

In this paper, we present experimental and theoretical studies on the interference between resonant and nonresonant photorecombinations for the main resonances of ground-state He-, Be-, B-, C-, N-, and O-like W ions. Experiments were done using a fast electron energy scanning technique at the upgraded Shanghai electron-beam ion trap. Asymmetric resonances were observed, and their Fano factors, which measure the interference degree, were determined. The calculations were done under the framework of Fano's theory by using the flexible atomic code, in which the relativistic configuration interaction method was employed. Among the nine resonances studied in this work, eight experimental results agree with the calculation within experimental uncertainties. But the experimental result for the resonance of Be-like W ions, through the intermediate state of ${[{(1s2{s}^{2}2{p}_{1/2})}_{1}2{p}_{3/2}]}_{5/2}$, deviates from its corresponding theoretical result by 1.3 times experimental uncertainty.

Upgrade of the electron beam ion trap in Shanghai.

Over the last few years the Shanghai electron beam ion trap (EBIT) has been successfully redesigned and rebuilt. The original machine, developed under collaboration with the Shanghai Institute of Applied Physics, first produced an electron beam in 2005. It could be tuned with electron energies between 1 and 130 keV and beam current up to 160 mA. After several years of operation, it was found that several modifications for improvements were necessary to reach the goals of better electron optics, higher photon detection, and ion injection efficiencies, and more economical running costs. The upgraded Shanghai-EBIT is made almost entirely from Ti instead of stainless steel and achieves a vacuum of less than 10(-10) Torr, which helps to minimize the loss of highly changed ions through charge exchange. Meanwhile, a more compact structure and efficient cryogenic system, and excellent optical alignment have been of satisfactory. The magnetic field in the central trap region can reach up till 4.8 T with a uniformity of 2.77 × 10(-4). So far the upgraded Shanghai-EBIT has been operated up to an electron energy of 151 keV and a beam current of up to 218 mA, although promotion to even higher energy is still in progress. Radiation from ions as highly charged as Xe(53+, 54+) has been produced and the characterization of current density is estimated from the measured electron beam width.

A portable high-resolution soft x-ray and extreme ultraviolet spectrometer designed for the Shanghai EBIT and the Shanghai low energy EBITs.

A portable high resolution soft x-ray and extreme ultraviolet (EUV) spectrometer has been developed for spectroscopic research at the Shanghai Electron Beam Ion Trap (EBIT) laboratory. A unique way of aligning the grazing incidence spectrometer using the zero order of the grating is introduced. This method is realized by extending the range of the movement of the CCD detector to cover the zero order. The alignment can be done in a few minutes, thus leading to a portable spectrometer. The high vacuum needed to be compatible with the EBITs is reached by mounting most of the translation and rotation stages outside the chamber. Only one high vacuum compatible linear guide is mounted inside the chamber. This is to ensure the convenient interchange of the gratings needed to enable wavelength coverage of the whole range of 10 to 500 Å. Spectra recorded with one of our low energy EBITs shows that a resolving power of above 800 can be achieved. In the slitless configuration used in this work, we found the resolving power to be limited by the width of the EBIT plasma. When mounted on the Shanghai EBIT which is a high energy EBIT and has a narrower EBIT plasma width, the estimated resolving power will be around 1400 at 221.15 Å.

Studies of space charge effects on operating electron beam ion trap at low electron beam energy

An electron beam ion trap (EBIT) is a powerful machine for disentangling studies of atomic processes in plasmas. To assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. Large amounts of simulation works were done to study the factors which hinder the EBIT from operation at very low electron beam energies. Under the guide line of the simulation results, we finally managed to successfully reach 60eV for the lower end of the electron beam energy with a beam transmission above 57%. In this presentation, simulation studies of the space charge effect, which is one of the most important causes of beam loss, was made based on Tricomp (Field precision).

KLL dielectronic recombination process of He-like to O-like xenon ions

In this work, the KLL dielectronic recombination (DR) processes of highly charged He-like to O-like xenon ions are studied systematically by using a DR program, which is based on the multi-configuration Dirac—Fock (MCDF) method. The KLL DR resonant energies and the corresponding resonant strengths are calculated, emphasizing especially the effect of the Breit interaction on the DR strengths. The theoretical KLL DR spectra are obtained and compared with the latest experimental results obtained in the Shanghai Electron Beam Ion Trap.

Electron beam density study using a portable slit imaging system at the Shanghai Electron Beam Ion Trap

In this work, a portable slit imaging system is developed to study both the electron beam diameter and the profile of the newly developed Shanghai Electron Beam Ion Trap (Shanghai EBIT). Images are detected by a charge coupled device (CCD) sensitive to both X rays and longer wavelength photons (up to visible). Large scale ray tracings were conducted for correcting the image broadening effects caused by the finite slit width and the finite width of the CCD pixels. A numerical de-convolution method was developed to analyse and reconstruct the electron beam density distribution in the EBIT. As an example of the measured beam diameter and current density, the FWHM (full width at half maximum) diameter of the electron beam at 81 keV and 120 mA is found to be 76.2 μm and the density 2.00 × 103 A·cm−2, under a magnetic field of 3 T, including all corrections.

A high-precision high-voltage divider applied to electron beam energy measurements

A high-precision high-voltage divider with a range of 85 kV was designed for electron beam energy measurements, particularly in the Shanghai electron beam ion trap (Zhu et al 2005 Nucl. Instrum. Methods Phys. Res. B 235 509). After minimizing the uncertainties caused by temperature fluctuations, including the effect of temperature on the resistance of the resistors, the divider was calibrated from 0 to 63 kV with a precision of less than 10 parts per million (ppm). During the calibration a parallel connection method was used to simplify the measurement.

A ray-tracing program and two cases of its application at the Shanghai EBIT laboratory

Based on ray-tracing procedures/techniques, we have carried out simulations on the operation of (i) a toroidal mirror used along with a vacuum ultraviolet scanning monochromator and (ii) variable line spacing gratings such as those used in flat-field spectrometers. In case (i), a toroidal mirror was installed in the optical beam line for normal incidence spectroscopy at the Shanghai electron beam ion trap (EBIT) (Zou Y and Hutton R 2005 Phys. Scr.T120 47) based on simulation results. Case (2) yielded results that can be used in aligning flat-field spectrometers; the results of the simulations were tested by experiment and were found to be in good agreement.

The status of the micro-calorimeter at the Shanghai EBIT

This paper contains a brief introduction to the main parameters of a micro-calorimeter designed to operate at the Shanghai electron beam ion trap. This is followed by short descriptions of some aspects of the calorimeter.

Overview of the Shanghai EBIT

EBIT (Electron Beam Ion Trap) is an excellent instrument both as light source and ion source, and is widely used in atomic physics research. In principle EBITs can produce ions of any charge state and of any element. In this report, a general introduction to the Shangai EBIT and short discussions of the spectroscopy platform are presented. Due to the repetitious running of the Shanghai EBIT over the past 5 years, it became necessary for the Shanghai EBIT to be disassembled for some maintenances and further modifications/improvements. The new design contains two major improvements. Furthermore, some experimental results on studies of dielectronic recombination processes for highly charged Xe ions will be discussed.

KLLdielectronic recombination resonant strengths of He-like up to O-like xenon ions

In this work, the $\mathrm{KLL}$ dielectronic recombination (DR) resonant strengths of He- through to O-like Xe ions were studied, both through experiment and calculation. The experiments were done using a fast electron beam-energy scanning technique at the Shanghai electron beam ion trap. The calculations were done by using the flexible atomic code (FAC), in which the relativistic configuration interaction (RCI) method was employed. For the total resonant strengths, the present experimental and theoretical results for He-, Be-, B-, C-, N-, and O-like Xe ions agree within experimental uncertainties (about 9%). But the experimental result for Li-like Xe is 14% higher than the calculation. The present FAC calculations of the total DR strengths were compared with the available previous calculations, using RCI or multiconfiguration Dirac-Fock (MCDF) methods, and the agreement was very good. In this work, some intermediate-state resolved $\mathrm{KLL}$ DR strengths were also obtained and compared with theoretical results, and more discrepancies were revealed.

Studies on resonant energies and strengths of the KLL dielectronic recombination processes for He- up to O-like xenon

KLL dielectronic recombination resonant energies and resonant strengths of He-like to O-like xenon were studied on Shanghai electron beam ion trap. Detailed relativistic calculations were also performed. Comparison between experimental and theoretical results showed reasonable agreement, while discrepancies were also found.

Precise experimental and theoretical studies on resonant energies of the KLL dielectronic recombination processes for He- up to O-like xenon

Dielectronic resonance energies were measured for high charge states of Xe using the Shanghai Electron Beam Ion Trap equipped with a high precision voltage divider. Fifteen experimental resonant energies were obtained at an average uncertainty level of 0.03%.