D. Lu

A very low energy compact electron beam ion trap for spectroscopic research in Shanghai.

In this paper, a new compact low energy electron beam ion trap, SH-PermEBIT, is reported. This electron beam ion trap (EBIT) can operate in the electron energy range of 60-5000 eV, with a current density of up to 100 A/cm(2). The low energy limit of this machine sets the record among the reported works so far. The magnetic field in the central drift tube region of this EBIT is around 0.5 T, produced by permanent magnets and soft iron. The design of this EBIT allows adjustment of the electron guns axial position in the fringe field of the central magnetic field. This turned out to be very important for optimizing the magnetic field in the region of the electron gun and particularly important for low electron beam energy operation, since the magnetic field strength is not tunable with permanent magnets. In this work, transmission of the electron beam as well as the upper limit of the electron beam width under several conditions are measured. Spectral results from test operation of this EBIT at the electron energies of 60, 315, 2800, and 4100 eV are also reported.

High resolution flat crystal spectrometer for the Shanghai EBIT

We report on a high resolution flat crystal spectrometer designed for the Shanghai EBIT. Its energy range is from 0.5 to 10 keV. Three crystals can be installed in the vacuum chamber simultaneously, and its effective Bragg angle can be covered from 15 degrees to 75 degrees . A vacuum version charge-coupled device detector is used for detection of photons. An energy resolution under 1 eV was reached in measurements of the 4.5 keV Kalpha(1) line by using an x-ray generator with a titanium anode. The spectrometer was also tested to operate well on the Shanghai EBIT by observing the lines of tungsten at around 3.2 keV.

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.

The relative cross section and kinetic energy distribution of dissociation processes of methane by electron impact

Electron-impact ionization and dissociation of methane (CH4) has been experimentally studied with a cold target recoil-ion momentum spectrometer. We report data for the formation of CHn+ (n = 0 ~ 3) relative to that of CH4+ as a function of incident electron energy from 20 to 200 eV. Good agreements are achieved with previous studies. The kinetic energy distribution of the recoil-ions is presented and the average kinetic energy released (KER) was obtained for formation of CH3+. Taking advantages of the supersonic jet expansion, the thermal motion contribution to the kinetic energy distribution of the recoil-ions was reduced. The results agree better with theoretical data than those from previous experimental studies.

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.

Responsivity calibration of the extreme ultraviolet spectrometer in the range of 175-435 Å

We reported the relative responsivity calibration of the grazing-incidence flat-field EUV spectrometer between 175 and 435 A by means of two methods. The first method is implemented by measuring the diffraction efficiency of the grating with synchrotron radiation light source. Considering the transmission efficiency and quantum efficiency of the other optical components in the spectrometer, the total responsivity was then obtained. The second one was carried out by measuring line emissions from C3+, N4+ and O3+ ions at Shanghai high temperature super conductor electron beam ion trap (SH-HtscEBIT). The EUV spectra were also simulated theoretically via a collisional radiative model. In the calculation, the second-order relativistic many-body perturbation theory approach based on the flexible atomic code was used to calculate the energy levels and transition rates; the close-coupling R-matrix approach and relativistic distorted wave method were utilized to calculate the collision strength of electron impact ...

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.

Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with ...

Plasma diagnostic-related activities at Shanghai EBIT

In this report, plasma diagnostic-related activities at the newly developed Shanghai electron-beam ion trap (EBIT) are reviewed. The density of the electron beam was measured by employing a slit imaging system, and the ion densities of bare and H-like Kr were studied using radiative recombination emissions of n= 1 processes. A first intrashell (KLL) dielectronic recombination resonant spectrum of xenon is also shown and discussed. Finally, ion density oscillations from possibly different mechanisms than those seen earlier at the Berlin EBIT are observed and discussed.