Electron Beam Ion Trap Research Articles

Prospect for attosecond laser spectra of highly charged ions

The spectra of highly charged ions (HCIs) are of great significance for astronomical observation, astrophysical model establishment, and test of quantum electrodynamics (QED) theory. However, the transitions of HCI are mostly in the extreme ultraviolet or even X-ray range, the excitation spectra of HCI measured by laser spectroscopy in laboratory are very limited due to lack of the suitable light source. Up to now, only few experiments on the spectra of HCIs performed on synchrotron radiation, free electron laser or heavy-ions storage ring have been reported, which are summarized in this work. With the development of attosecond technology, several attosecond light source facilities have been built, such as extreme light infrastructure attosecond light pulse source (ELI-ALPS) and synergetic extreme condition user facility (SECUF), which have high photon energy and ultra-short pulse duration in the extreme ultraviolet and even soft X-ray range, providing new opportunities for laboratory research on HCI spectra and ultra short energy level lifetimes. Electron beam ion trap (EBIT), electron cyclotron resonance (ECR), and heavy-ion storage ring are usually used to generate ion target. But it is difficult to combine the attosecond laser source with large scale facility of HCI, for none of laboratories has both these two facilities now. Thus, two possible experimental schemes for attosecond spectrum of HCIs are proposed in this work. One scheme is that an EBIT can be designed as a terminal of attosecond laser facility, such as ELI-ALPS and SECUF, which can output different laser beams with high photon energy, ultra-short pulse duration or high flux. Another scheme is that a table-top HHG system pumped by an all-solid-state femtosecond laser or fiber femtosecond laser with high power can be combined with heavy-ion storage ring, such as ESR, CSRe, HIAF, and FAIR. Owing to high energy of ions in storage ring, the measurable energy levels of HCIs can even be extended to keV by the Doppler shift. Three different measurement methods: fluorescence detection, ion detection and attosecond absorption spectroscopy, can be used to obtain the HCI spectrum. Finally, a preliminary experimental setup for attosecond laser spectrum of HCI is proposed. The proposal on combining extreme ultraviolet attosecond light source with HCI target is discussed, and the feasibility of attosecond time-resolved precision spectrum for HCI is analyzed according to the typical parameters of attosecond light source and the known excitation cross-section and detection efficiency, which can provide a new platform for implementing ion level structure calculation, QED theory high-precision test and astronomical spectroscopic observation. It can be used to measure the ultra-short lifetime, low excitation cross-section ionic energy level, and even some transitions with large energy interval. We hope that this work can provide a reference for the experimental measuring of HCI spectrum and ion energy level lifetime in future.

Optical Lines of Ru21+ to Ru24+ Ions

In this work, we report a spectroscopy measurement of Ru21+ to Ru24+ ions in the optical region using a low energy electron beam ion trap. Twelve lines were observed. The multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods were used to calculate the atomic level energies and the transition rates. With the assistance of the theoretical results, eleven magnetic dipole lines were identified. The experimental results provide new reference data for further theoretical investigations of the complex ions.

High-Resolution Laboratory Measurements and Identification of Fe IX Lines near 171 Å

A multitude of weaker Fe IX lines have been predicted in the vicinity of the strong 171 Å line that dominates the spectra of many astrophysical and laboratory sources. Some of these weaker lines have only recently been identified in the laboratory, albeit some only tentatively. Here, we present measurements on the Livermore EBIT-I electron beam ion trap that span the region from 170.0 to 173.6 Å, which surrounds the 171 Å line. The measurements stepped through electron beam energy to determine the charge state of iron associated with each observed feature. Moreover, we have minimized the presence of oxygen in the trap, because oxygen lines obscured possible Fe IX lines in past measurements and prevented their identification. Our measurement confirms formerly tentative identifications and adds several new assignments.

Laboratory Search for Fe IX Solar Diagnostic Lines Using an Electron Beam Ion Trap

The Fe IX spectrum features two lines in the extreme ultraviolet whose ratio has been rated among the best density diagnostics in the solar spectrum. One line is an E1-allowed intercombination transition at 244.909 Å, the other an E1-forbidden M2 transition at 241.739 Å. Employing a medium and a high resolution spectrometer at the Livermore EBIT-I electron beam ion trap, we have observed the line pair in the laboratory for the first time. Using a CHIANTI model computation, the observed line ratio yields a value of the electron density that is compatible with typical densities in our device.

The M1 transitions and visible spectra of W13+ ion

The theoretical visible transitions and spectra of W13+ ion from the Electron Beam Ion Trap are investigated by constructing and solving a collisional-radiative model (CRM) within the Quasi-Steady-State approximation. The necessary atomic data for constructing the CRM have been calculated using the relativistic configuration interaction (RCI) method and distorted wave approximation. The present results are in reasonable agreement with the available experimental observations and theoretical calculations. The relative intensities of the M1 transitions between the ground and low-lying excited fine-structure levels have been found to strongly depend on the electron density from ne=109 cm−3 to ne=1012 cm−3, which might be useful for the future diagnosis of the electron density of the plasma.

Time-dependent Lattice Cross Sections and Line Ratios for Solar Wind Charge Exchange: Bare Ne Incident on Atomic H and He

Charge exchange (CX) between highly charged ions and neutrals within the geocorona and heliosphere introduces a problematic background for every X-ray observation. For H-like ions the ℓ states within each n shell are degenerate. The majority of CX spectral models rely on calculated n-resolved cross sections, and the distribution of ℓ states is assumed to follow one of several analytical expressions. Laboratory data to validate these distributions at solar wind velocities is not available. Explicitly velocity-dependent calculations of n ℓ-resolved CX cross sections using the time-dependent lattice (TDL) method for Ne10+ incident on atomic H and He at 1–5 keV amu−1 are reported. The cross sections are incorporated into a radiative cascade model, and the influence of n- and n ℓ-resolved cross sections on possibly diagnostic emission line ratios is investigated. Comparisons of the ℓ distribution extracted from the TDL cross sections to the predominantly used analytical distributions reveals a consensus among n and n ℓ-resolved data at solar wind velocities, suggesting a statistical distribution is most appropriate for CX collisions involving atomic H. No consensus is found for atomic He targets, and the ℓ distribution extracted from n ℓ-resolved cross sections appears most appropriate. Open questions related to CX are discussed with emphasis on experimental methods to resolve them. Spectral measurements at an electron beam ion trap facility are planned to benchmark the presented cross section data.

First Laboratory Measurement of Magnetic-field-induced Transition Effect in Fe x at Different Magnetic Fields

The magnetic field is extremely important for understanding the properties of the solar corona. However, there are still difficulties in the direct measurement of the coronal magnetic field. The magnetic-field-induced transition (MIT) in Fe x, appearing in coronal spectra, was discovered to have prospective applications in coronal magnetic field measurements. In this work, we obtained the extreme ultraviolet spectra of Fe x in the wavelength range of 174–267 Å in the Shanghai High-temperature Superconducting Electron Beam Ion Trap, and examined the effect of MIT in Fe x by measuring the line ratios between 257.262 Å and the reference line of 226.31 Å (257/226) at different magnetic field strengths for the first time. The electron density that may affect the 257/226 value was also obtained experimentally and verified by comparing the density-sensitive line ratio (175.266 Å/174.534 Å) measurements with the theoretical predictions, and there was good agreement between them. The energy separation between the two levels of 3s23p43d 4 D 5/2 and 3s23p43d 4 D 7/2, one of the most critical parameters for determining the MIT rate, was obtained by analyzing the simulated line ratios of 257/226 with the experimental values at the given electron densities and magnetic fields. Possible reasons that may have led to the difference between the obtained energy splitting and the recommended value in previous works are discussed. Magnetic field response curves for the 257/226 value were calculated and compared to the experimental results, which is necessary for future MIT diagnostics.

Direct wavelength measurement of the [formula omitted][formula omitted] highly charged ion clock transition in Rh[formula omitted

Magnetic dipole transitions between fine- or hyperfine-structure splitting in the np23P ground term have been proposed to develop ultraprecise atomic clocks (https://link.aps.org/doi/10.1103/PhysRevLett.113.233003 Yudin etal., Phys. Rev. Lett. 113 (2014) 233003). In the present work, a spectroscopic investigation of fine-structure splitting of 4p23P1−3P0 in Rh13+ is performed in a compact electron beam ion trap. By means of a dedicated internal calibration method, the transition wavelength of 321.2150(14) nm (in air) is precisely determined at a few ppm level which agrees with the previous results and improves its uncertainty by more than 350 times.

Fast silicon carbide MOSFET based high-voltage push-pull switch for charge state separation of highly charged ions with a Bradbury-Nielsen gate.

In this paper, we report on the development of a fast high-voltage switch, which is based on two enhancement mode N-channel silicon carbide metal-oxide-semiconductor field-effect transistors in push-pull configuration. The switch is capable of switching high voltages up to 600V on capacitive loads with rise and fall times on the order of 10ns and pulse widths ≥20ns. Using this switch, it was demonstrated that, from the charge state distribution of bunches of highly charged ions ejected from an electron beam ion trap with a specific kinetic energy, single charge states can be separated by fast switching of the high voltage applied to a Bradbury-Nielsen Gate with a resolving power of about 100.

Magnetic-dipole lines in Fe-like and Mn-like molybdenum ions

Optical spectra of Fe-like Mo16+ and Mn-like Mo17+ ions were measured using the newly developed low-energy electron-beam ion trap at Fudan University. The observed emission spectra incorporated six lines from Mo16+ ions and five lines from Mo17+ ions. These eleven lines included ten lines that were measured for the first time. Spectra modeling was carried out based on the collisional-radiative (CR) modeling implemented in the flexible atomic code. Overall, a reasonable agreement of wavelengths and intensities was found between the experimental results and the CR modeling. It is demonstrated that ten of the eleven observed lines arised from the magnetic-dipole transitions within the ground configurations of Mo16+ and Mo17+ ions. Furthermore, the electron-density dependence of the line intensity ratios was investigated in the range of 109−1013 cm−3 using CR modeling. The theoretical ratios were consistent with the experimental line intensity ratios for two electron densities of 3.27×1011 cm−3 and 2.56×1011 cm−3. Moreover, several line intensity ratios were found to be sensitive to the electron density. The potential applications of these electron-density sensitive lines were demonstrated for plasma diagnostics.

Simulations of a new electron gun for the TITAN EBIT

Penning trap mass spectrometry is the tool of choice for mass measurements to test the Standard Model or lay the nuclear-physics foundation of neutrino physics due to the high precisions achievable. This precision can be further boosted by higher charge states (Ettenauer et al 2011). For this purpose, an electron beam ion trap (EBIT) provides radioactive HCIs at the TITAN facility at TRIUMF. To improve the electron beam properties and its control, a new electron gun is under development. The electron gun within its TITAN EBIT environment was simulated using Field Precision’s TRAK software. A new electrode geometry was chosen and optimized to extract up to 5A, 66 keV electron beams. Due to the strong fringe field of the unshielded 6T magnet, options for the passive and active shielding of the gun were explored to compress the electron beam. During the design process, careful attention was paid to safety and mechanical considerations. Simulations and the status of the new electron gun will be presented.

Progress of the High-Current EBIS Charge Breeder for the FRIB

The ReA post-accelerator of the National Superconducting Cyclotron Laboratory employs an Electron-Beam Ion Trap (EBIT) as a charge breeder to reaccelerate rare-isotope beams to several MeV/u. The Facility for Rare-Isotope Beams (FRIB) is near completion and will provide RIB rates expected to exceed in some cases 1010 particles/s. The ReA EBIT operates with an electron current of 300 – 600 mA, corresponding to an electron current density of 170 – 340 A/cm2 and a maximum trap capacity of 1010 elementary charges, which can be insufficient to handle high FRIB rates. A High-Current Electron-Beam Ion Source (HCEBIS) has been constructed based on the backbones of the TEST EBIS from the Brookhaven National Laboratory. By using a 4-A electron beam, a current density of 298 A/cm2 and a maximum trap capacity of 2.4×10n elementary charges can be achieved. This paper presents the status of the HCEBIS. It also includes results of electron- and ion-beam simulations and discusses electron-beam commissioning plans.

Charge-state evolution from W5+ to W7+ at energies below the ionization potentials

Experiments on an electron-beam ion trap (EBIT) and calculations using flexible atomic code (FAC) are carried out to study the charge-state evolution from ${\mathrm{W}}^{5+}$ to ${\mathrm{W}}^{7+}$. The ${\mathrm{W}}^{7+}$ line at 574.47 nm is observed with an electron-beam energy of about 48 eV, which is far below the ionization potentials of ${\mathrm{W}}^{5+}$ (65 eV) and ${\mathrm{W}}^{6+}$ (122 eV). Multicharge-state collisional-radiative (CR) calculations for ${\mathrm{W}}^{5+}, {\mathrm{W}}^{6+}$, and ${\mathrm{W}}^{7+}$ are performed with level-to-level processes with configuration interaction (CI), including direct ionization, collision excitation, radiative recombination, charge exchange, radiative transition, and autoionization. The CI strongly influences the calculated ionization cross sections for metastable levels. The CR-simulated spectra agree well with the experiments, and the calculated effective ionization cross section for ${\mathrm{W}}^{6+}$ has the same trend as the available experimental data [M. Stenke et al., J. Phys. B: At. Mol. Opt. Phys. 28, 2711 (1995)]. The metastable levels (\ensuremath{\sim}40 eV for ${\mathrm{W}}^{5+}$; \ensuremath{\sim}40 and \ensuremath{\sim}85 eV for ${\mathrm{W}}^{6+}$) significantly contribute to the ionization through excitation-autoionization at rather low energies (50 eV) in the EBIT plasma. These metastable levels could have a considerable influence on the charge-state evolution of tungsten ions in edge fusion plasma.

Z -dependent crossing of excited-state energy levels in highly charged galliumlike lanthanide atomic ions

Extreme ultraviolet (EUV) optical transitions of lanthanide highly charged ions have been studied. The $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4{s}^{2}4d$ and $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4s4{p}^{2}$ transition lines of galliumlike lanthanide elements have been spectroscopically measured in large helical device (LHD) plasma and electron-beam ion trap (EBIT) plasma. The wavelengths for Eu ions agreed within $0.03%$ between the LHD and EBIT measurements. Due to the enhancement of spin-orbit interactions along with the increase of atomic number $Z$ in $4p$ atomic orbitals, energy splitting between $4{p}_{1/2}$ and $4{p}_{3/2}$ orbitals increases significantly from lanthanum to lutetium, causing the crossing of $Z$-dependent wavelength curves. The spectral line positions and strengths are theoretically calculated by means of the multiconfiguration Dirac-Fock method. The mixing of the $[\mathrm{Ni}]4{s}^{2}4d$ and $[\mathrm{Ni}]4s4{p}^{2}$ configurations leads to an avoided crossing in the apparent wavelength curves. The configuration mixing makes both the $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4{s}^{2}4d$ and $[\mathrm{Ni}]4{s}^{2}4p--[\mathrm{Ni}]4s4{p}^{2}$ lines well visible in the EUV spectra near the level crossing point. The levels are found to cross between $Z=62$ and 63.

Polarization measurement of L -shell radiative recombination x rays from highly charged bismuth ions

We report a polarization measurement of $L$-shell radiative recombination (RR) x rays emitted from He- to F-like bismuth ions. The polarization feature was obtained from the azimuthal angular distribution of the Compton-scattered RR x rays detected with a recently developed state-of-the-art Compton polarimeter installed on an electron beam ion trap. This is one of a very few polarization measurements of RR x rays ever conducted and the first one with bismuth ions. We derived the degree of linear polarization averaged over the charge states to be $0.666\ifmmode\pm\else\textpm\fi{}0.014$. By contrast, a theoretical estimation of the degree of polarization with the Flexible Atomic Code (fac) yields $0.716\ifmmode\pm\else\textpm\fi{}0.023$. The discrepancy between the observed and theoretical values is likely to be due to the electron correlation effects.

Re-investigation and line identifications for W11+ in the visible range

We present a new investigation of unidentified emission lines in 350–660 nm from W11+ at a compact electron-beam ion trap in Shanghai. To help the line identification, transition energies of the lowest 48 levels are calculated by the large-scale relativistic configuration interaction and multiconfiguration Dirac–Hartree–Fock calculation. The results from the two calculations are in good agreement with each other and the deviation is 0.66% on average. By using the collisional-radiative model implemented in the flexible atomic code, six observed lines for the visible spectrum of W11+ are identified as magnetic-dipole transitions from 4f 125s 25p 3 and 4f 135s 25p 2 configurations.

Re-investigation and line identifications for W11+ in the visible range

Abstract We present a new investigation of unidentified emission lines in 350–660 nm from W11+ at a compact electron-beam ion trap in Shanghai. To help the line identification, transition energies of the lowest 48 levels are calculated by the large-scale relativistic configuration interaction and multiconfiguration Dirac-Hartree-Fock calculation. The results from the two calculations are in good agreement with each other and the deviation is 0.66% on average. By using the collisional-radiative model implemented in the flexible atomic code, six observed lines for the visible spectrum of W11+ are identified as magnetic-dipole transitions from 4f125s25p3 and 4f135s25p2 configurations.

Modeling the wavelength of unresolved transition arrays in the extreme ultraviolet region from Sn to Hf ions by combining theoretical and experimental spectral data

This paper proposes a method to determine the wavelength of unresolved transition arrays (UTAs) in the extreme ultraviolet (EUV) wavelength region from Sn to Hf plasma by combining calculated and experimental data. Based on a computational analysis of the atomic structure, we show that the wavelength of UTAs can be explained using the screening theory by a simple quadratic formula using the effective core charge and the screening constant for 4d electrons as parameters. The results from the model were compared with experiments to reproduce the trend of the spectrum, which has a minimum wavelength with respect to the ion charge. The wavelength is shown to agree with experiment over Pd- to Sr-like ions by applying a small shift that was determined using the spectrum observed in the electron beam ion trap. The present model would allow us to calculate the opacity of Sn plasmas with much smaller computational time than using present large-scale collisional radiative models, with fewer energy levels and parameterized rate coefficients, which will be also useful to investigate the efficiency of the EUV light source.

Ion energy distribution in an electron beam ion trap inferred from simulations of the trapped ion cloud.

We have inferred the energy distribution of trapped ions in an electron beam ion trap (EBIT) from simulations of the spatial distribution of Fe^{13+} ions and a comparison with measured visible light images of the ion cloud. We simulated the cloud of Fe^{13+} ions by computing ion trajectories in the EBIT for different ion energy distributions used to initialize the trajectories. We then performed a least-squares fit to infer the ion energy distribution that best reproduced the measured ion cloud. These best-fit distributions were typically non-Maxwellian. For electron beam energies of 395-475eV and electron beam currents of 1-9 mA, we find that the average ion energy is in the range of 10-300eV. We also find that the average ion energy increases with increasing beam current approximately as 〈E〉≈25I_{e}eV, where I_{e} is the electron beam current in mA. We have also compared our results to Maxwell-Boltzmann-distribution ion clouds. We find that our best-fit non-thermal distributions have an 〈E〉 that is less than half that of the T from the best-fit Maxwell-Boltzmann distributions (〈E〉/q)/T=0.41±0.05.

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.