Yunqing Fu

Precise studies on resonant energies of the first intershell (KLL) dielectronic recombination processes for He- up to O-like xenon

Precise studies of the resonant energies of KLL dielectronic recombination (DR) processes of He-, Li-, Be-, B-, C-, N-, and O-like xenon ions were performed at the Shanghai Electron Beam Ion Trap [X. Zhu et al., Nucl. Instrum. Methods Phys. Res. B 235, 509 (2005)], employing home developed high precision, high stability high voltage dividers. Influences from retardation by the capacitor of experimental setup, contact potential, space charge of the electron beam, and of ion neutralization, as well as fringing field effects were taken into account. The obtained resonant energies were, at an average uncertainty level of 0.03%, compared with calculation results by relativistic configuration interaction (RCI) theory, relativistic many-body perturbation theory (RMBPT), and by multiconfiguration Dirac–Fock (MCDF) theory. All the three predicted DR resonant energies by MCDF agree with our experiments. Among the 15 predictions by RMBPT, 13 are in good agreement with our experimental results. But only five out of 1...

Progress at the Shanghai EBIT

In this report, a brief description of the progress of the Shanghai EBIT project is presented. This is followed by short discussions on the X ray spectra at several electron beam energies and the ion densities in the EBIT at a specific running condition.

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.

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 disassem- bled for some maintenances and further modifications/improvements. The new design contains two major improvements. Furthermore, some experimental results on studies of dielectronic recombi- nation processes for highly charged Xe ions will be discussed.

High precision high voltage divider and its application to electron beam ion traps.

A high precision high voltage divider has been developed for the electron beam ion trap in Shanghai. The uncertainty caused by the temperature coefficient of resistance (TCR) and the voltage coefficient of resistance has been studied in detail and was minimized to the level of ppm (10(-6)) range. Once the TCR was matched between the resistors, the precision of the dividing ratio finally reached the ppm range also. We measured the delay of the divider caused by the capacitor introduced to minimize voltage ripple to be 2.35 ms. Finally we applied the divider to an experiment to measure resonant energies for some dielectronic recombination processes for highly charged xenon ions. The final energies include corrections for both space charge and fringe field effects are mostly under 0.03%.

Progress of the spectroscopy research platform at the Shanghai electron beam ion trap

In this report we will focus on spectrometer development, spectroscopic studies and a few other recent developments at the Shanghai Electron Beam Ion Trap, EBIT laboratory. Currently the Shanghai EBIT has three spectrometers covering totally the wavelength region of 1 to 10000 A. Two of these instruments are home made. A flat crystal spectrometer covers the wavelength range of around 1 - 20 A while a flat field instrument covers the range of around 20 - 400 A. The 3rd instrument is a commercial McPherson 225 normal incidence spectrometer. All spectrometers employ CCD cameras for photon detection. The Shanghai EBIT is also equipped with high purity Germanium detectors for, amongst other things, dielectronic recombination studies and time evolution studies of ion distributions. To back up these experimental studies computer codes have been developed for calculation of charge state balances etc. Parallel to the experimental program we have also developed experience at running a number of atomic structure codes (MCHF, MCDF, FAC) for various systems, e.g. the M3 decay of the 3d94s 3D3 for Ni-like ions.

Modified miniature metal vapor vacuum arc source for the Shanghai electron beam ion trap

A modified miniature metal vapor vacuum arc ion source has been developed for the Shanghai electron beam ion trap. Several kinds of elements have been tested to extract lowly charged ions, such as Fe, Au, Ge, Mo, Ti, Al, and Cu. Besides high enough ion beam current and a short pulse width, we focus on the operation reliability, long term operation, and convenience of use.

Dielectronic recombination studies based on EBIT

Dielectronic recombination (DR) process plays an important role in high temperature plasmas, where DR can affect charge balance and level populations significantly, and can cause radiative energy loss. Resolvable DR sourced satellite lines are often used for plasma temperature diagnostics, while the un-resolvable ones disturb determining spectral line shape, line intensity, and line position. Data of DR resonant strength is vital for accurate modeling of high temperature plasmas. DR studies are also important for testing atomic structure and atomic collision theories, since they carry information on quantum electrodynamics, relativistic effects, electron correlations and so on. Electron beam ion trap (EBIT) is an accelerator type device, which is capable of acting as both ion sources and light sources. EBIT can produce a special sort of plasma, in which electron energy is tunable and has a very narrow distribution. This made it possible for disentanglement studies on electron ion collision processes in plasmas. In this paper, experimental studies of DR processes based on electron beam ion traps (EBIT) will be discussed.

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.

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.