Compact Electron Beam Ion Trap Research Articles

The 3d 2 D 5/2−2 D 3/2 magnetic dipole transition in potassium-like ions

Spectral lines of the magnetic-dipole transition between the 3d2D3/2,5/2 levels of K-like Kr17+, Zr21+, Nb22+, Mo23+, and Ru25+ ions were measured in a compact electron beam ion trap. By means of dedicated calibration methods, the transition wavelengths of Kr17+, Zr21+, and Mo23+ ions reduce uncertainties by at least one order of magnitude and the wavelengths of Nb22+ and Ru25+ ions are measured for the first time at a few ppm level. In addition, the fine-structure energy splittings were systematically calculated using the multiconfiguration Dirac–Hartree–Fock method combined with the relativistic configuration interaction approach. The contributions of the core-valence and core-core electron correlations, the Breit interaction and QED effect were discussed in detail. The results show that it is essential to include deep core-valence correlation of L-shell and core-core valence correlation of 3p subshell to obtain an agreement better than 0.15% with existing experimental values. The calculation model can be performed to predict the wavelength within a high accuracy for a wide range of potassium-like ions.

Identification of Visible Lines in Pm-like W13+

To provide spectroscopic data for W13+, the present work is focused on the analysis of spectra observed in the visible range, using a compact electron beam ion trap (CoBIT). Line identification is done by using a collisional radiative model, along with sophisticated structure calculations from FAC and GRASP2018. Most of the identified lines belong to magnetic dipole (M1) transitions between the levels of the 4f125p1 and 4f13 configurations.

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.

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.

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.

Evaluation of Fe XIV Intensity Ratio for Electron Density Diagnostics by Laboratory Measurements

The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.

A compact electron beam ion trap in support of high-temperature plasma diagnostics based on conduction-cooled superconducting coils.

Spectroscopic diagnostics of future fusion reactor plasmas require information on impurity line emissions, especially for relevant high-Z metal elements (e.g., tungsten). These materials will be widely used as plasma facing components for their high heat tolerance and low sputtering yield. Based on an electron beam ion trap, a compact impurity spectra platform is developed to mimic the high-temperature environment of a fusion reactor. The proposed platform can deliver a focused e-beam at energies over 30 keV using a confining magnetic field of ∼1.0T generated by two superconducting coils (NbTi). Cooled by a closed-loop cryocooler, the coils can avoid the usage of a complicated cryogenic system involving the handling of liquid helium. For spectroscopic studies of highly charged ions, a spherically curved crystal spectrometer is proposed to measure a wavelength range around 2-4 Å covering the typical wavelength range expected to be emitted by metal ions in a fusion plasma. This paper reports the design and development progress of the platform.

Visible spectra of W8+ in an electron-beam ion trap

To provide spectroscopic data for lowly charged tungsten ions relevant to fusion research, this work focuses on the ${\mathrm{W}}^{8+}$ ion. Six visible spectra lines from ${\mathrm{W}}^{8+}$ in the range of 420--660 nm are observed with a compact electron-beam ion trap in Shanghai. Furthermore, transition energies are calculated for the 30 lowest levels of the $4{f}^{14}5{s}^{2}5{p}^{4}, 4{f}^{13}5{s}^{2}5{p}^{5}$, and $4{f}^{12}5{s}^{2}5{p}^{6}$ configurations of ${\mathrm{W}}^{8+}$ by using the flexible atomic code (fac) and grasp package. Reasonably good agreement is found between our two independent atomic-structure calculations. The resulting atomic parameters are adopted to simulate the spectra based on the collisional-radiative model implemented in the fac code. This assists us with identification of six strong magnetic-dipole transitions in the $4{f}^{13}5{s}^{2}5{p}^{5}$ and $4{f}^{12}5{s}^{2}5{p}^{6}$ configurations from our experiments.

Probing multiple electric-dipole-forbidden optical transitions in highly charged nickel ions

Highly charged ions (HCIs) are promising candidates for the next generation of atomic clocks, owing to their tightly bound electron cloud, which significantly suppresses the common environmental disturbances to the quantum oscillator. Here we propose and pursue an experimental strategy that, while focusing on various HCIs of a single atomic element, keeps the number of candidate clock transitions as large as possible. Following this strategy, we identify four adjacent charge states of nickel HCIs that offer as many as six optical transitions. Experimentally, we demonstrated the essential capability of producing these ions in the low-energy compact Shanghai-Wuhan Electron Beam Ion Trap. We measured the wavelengths of four magnetic-dipole ($M$1) and one electric-quadrupole ($E$2) clock transitions with an accuracy of several ppm with a novel calibration method; two of these lines were observed and characterized for the first time in controlled laboratory settings. Compared to the earlier determinations, our measurements improved wavelength accuracy by an order of magnitude. Such measurements are crucial for constraining the range of laser wavelengths for finding the "needle in a haystack" narrow lines. In addition, we calculated frequencies and quality factors, evaluated sensitivity of these six transitions to the hypothetical variation of the electromagnetic fine structure constant $\alpha$ needed for fundamental physics applications. We argue that all the six transitions in nickel HCIs offer intrinsic immunity to all common perturbations of quantum oscillators, and one of them has the projected fractional frequency uncertainty down to the remarkable level of 10$^{-19}$.

Resonant electron impact excitation of highly charged Fe ions studied with a compact electron beam ion trap

AbstractWe present extreme ultraviolet spectra of 3s3p–3s3d transitions in Fe14+ observed with a compact electron beam ion trap. The contributions of indirect excitation via a metastable state and resonant excitation are studied by observing the electron energy dependence of the spectra for the energy range of 60–210 eV. The results indicate that the 3s3d 1D2 level is directly excited from the 3s2 ground state whereas the 3s3d 3D3 level has a large contribution of the indirect excitation via the 3s3p 3P2 metastable state. Comparisons with the theoretical excitation cross sections including MNn resonant excitations show good qualitative agreement with the experimental results for the electron energy dependent features.

Direct determination of the energy of the first excited fine-structure level in Ba6+

We present an experimental observation of the visible magnetic dipole transition between the fine structure levels in the ground term of ${\mathrm{Ba}}^{6+}$ ($5s{\phantom{\rule{0.16em}{0ex}}}^{2}5{p}^{2}$: $^{3}P_{0}\ensuremath{-}^{3}P_{1}$) with a compact electron beam ion trap. The wave number in vacuum of the transition is determined to be 15505.506(37) ${\mathrm{cm}}^{\ensuremath{-}1}$ by simultaneously observing the reference lines of neutral Ne. The present measurement reduces the uncertainty in the previously reported value obtained from observation of the electric dipole transitions to the ground terms in the extreme ultraviolet range [Phys. Scr. 46, 403 (1992)].

A low-energy compact Shanghai-Wuhan electron beam ion trap for extraction of highly charged ions.

A low-energy, compact, and superconducting electron beam ion trap (the Shanghai-Wuhan EBIT or SW-EBIT) for extraction of highly charged ions is presented. The magnetic field in the central drift tube of the SW-EBIT is approximately 0.21 T produced by a pair of high-temperature superconducting coils. The electron-beam energy of the SW-EBIT is in the range of 30-4000 eV, and the maximum electron-beam current is up to 9 mA. Acting as a source of highly charged ions, the ion-beam optics for extraction is integrated, including an ion extractor and an einzel lens. A Wien filter is then used to measure the charge-state distribution of the extracted ions. In this work, the tungsten ions below the charge state of 15 have been produced, extracted, and analyzed. The charge-state distributions and spectra in the range of 530-580 nm of tungsten ions have been measured simultaneously with the electron-beam energy of 279 eV and 300 eV, which preliminarily indicates that the 549.9 nm line comes from W14+.

Visible spectra of heavy ions with an open 4f shell

We present visible to near‐infrared spectra of highly charged Yb (the atomic number 70) and W (74) obtained with a compact electron beam ion trap. By observing the dependence on the electron beam energy, the charge state that should be assigned to the observed lines is determined. For In‐like Yb21+ and W25+ and Sn‐like W24+, the experimental spectra are compared with theoretical calculations done by the CI+all‐order method. In each spectrum, the most prominent line is identified as the magnetic dipole transition from the first excited fine structure level to the ground level in the ground electronic configuration, 4f3 for In‐like ions and 4f4 for Sn‐like ions.

Visible transitions in Ag-like and Cd-like lanthanide ions

We present visible spectra of Ag-like ($4d^{10}4f$) and Cd-like ($4d^{10}4f^2$) ions of Ho (atomic number $Z=67$), Er (68), and Tm (69) observed with a compact electron beam ion trap. For Ag-like ions, prominent emission corresponding to the M1 transitions between the ground state fine structure splitting $4f_{5/2}$--$4f_{7/2}$ is identified. For Cd-like ions, several M1 transitions in the ground state configuration are identified. The transition wavelength and the transition probability are calculated with the relativistic many-body perturbation theory and the relativistic CI + all-order approach. Comparisons between the experiments and the calculations show good agreement.

Emission line spectra of the 2s-2p transitions of S VIII-S XIII in the extreme ultraviolet region 160-300 Å

SynopsisThe extreme ultraviolet spectra of S VIII-S XIII have been measured using compact electron beam ion trap in the wavelength range of 160-300 Å. We have identified several lines by observing electron energy dependence between 365 and 680 eV and with the support of collisional radiative modeling data obtained with the FAC code. The measured wavelengths are found in good agreement with the calculated and previous reported results.

Extreme ultraviolet spectra of S IX and S X relevant to solar coronal plasmas

We present extreme ultraviolet laboratory spectra of highly charged S IX and S X measured using a compact electron beam ion trap. The data were recorded using a flat-field grazing incidence spectrometer in the wavelength range between 210 and 290Å. The beam energy was tuned for three different values at 365, 410 and 465eV while keeping electron beam current constant at 10mA. By measuring the beam energy dependence, we identified several lines originating from S IX and S X ions with the support of collisional-radiative modeling. We compared them with the present calculations and transitions listed in the NIST data base and found in good agreement.

Population trapping: The mechanism for the lost resonance lines in Pm-like ions

We report a population kinetics study on line emissions of the Pm-like Bi22+ performed by using a collisional-radiative (CR) model. Population rates of excited levels are analyzed to explain the population trapping in the 4f135s2 state which causes the loss of the 5s−5p resonance lines in emission spectra. Based on the present analysis, we elucidate why the population trapping is not facilitated for a meta-stable excited level of the Sm-like Bi21+. The emission line spectra are calculated for the Pm-like isoelectronic sequence from Au18+ through W13+ and compared with experimental measurements by electron-beam-ion-traps (EBITs). Structures of the spectra are similar for all of the cases except for calculated W13+ spectra. The calculated spectra are hardly reconciled with the measured W13+ spectrum using the compact electron-beam-ion-trap (CoBIT) [Phys. Rev. A 92 (2015) 022510].

Measurements of density dependent intensity ratios of extreme ultraviolet line emission from Fe X, XI, and XII

We report high-resolution density dependent intensity ratio measurements for middle charge states of iron in the extreme ultraviolet (EUV) spectral wavelength range of 160−200 A. The measurements were performed at the Tokyo EBIT laboratory by employing a flat-field grazing incidence spectrometer installed on a low energy compact electron beam ion trap. The intensity ratios for several line pairs stemming from Fe X, Fe XI and Fe XII were extracted from spectra collected at the electron beam energies of 340 and 400 eV by varying the beam current between 7.5 and 12 mA at each energy. In addition, the effective electron densities were obtained experimentally by imaging the electron beam profile and ion cloud size with a pinhole camera and visible spectrometer, respectively. In this paper, the experimental results are compared with previous data from the literature and with the present calculations performed using a collisional-radiative model. Our experimental results show a rather good agreement with the calculations and previous reported results.

High resolution EUV spectroscopy of xenon ions with a compact electron beam ion trap

We performed high resolution extreme ultraviolet (EUV) spectroscopy measurements of highly charged xenon ions with a compact electron beam ion trap. The spectra were recorded with a flat-field grazing incidence spectrometer while varying the electron beam energy between 200 and 890eV. We measured the wavelengths for several lines of Rh-like Xe9+ - Cd-like Xe6+ and Cu-like Xe25+- Se-like Xe20+ in the range of 150–200Å with an uncertainty of 0.05Å. Previously, most of these lines have been reported from EBITs with a wavelength uncertainty of 0.2Å. Additionally, based on the electron beam energy dependence of the observed spectra we tentatively identified three new lines, which were reported as unidentified lines in the previous studies.