Highly Charged Ions Research Articles

Enhanced energy deposition of laser-produced proton beams in high-density plasmas due to beam density self-steepening

The energy deposition of laser-accelerated proton beams in solid-density plasmas with different ion charge numbers is studied with detailed one-dimensional particle-in-cell simulations. In the plasma with a high ion charge number, in which the plasma collision frequency approaches electron oscillation frequency, the beam protons are strongly decelerated by the electric field induced by the plasma return current. The energy deposition is further enhanced as the beam travel distance increases due to beam density self-steeping, which is also confirmed by multi-dimensional particle-in-cell simulation. A simple analytical model is proposed to estimate the characteristic travel distance for significant density self-steeping, showing agreement with the simulation results. While in the plasma with a low ion charge number, in which the plasma collision frequency is much smaller than the electron oscillation frequency, the proton beam is modulated significantly by the excited two-stream instability.

The MUSIC Critical Benchmark and Nuclear Data

The Measurement of Uranium Subcritical and Critical (MUSIC) experiment was a series of measurements of critical and subcritical configurations of bare highly enriched uranium. The goal was to compare measurement methods, analysis techniques, and simulation methods across regimes of criticality and to provide high-quality validation of 235U nuclear data. A benchmark evaluation of the two critical configurations of the MUSIC experiments will soon be published in the release of the International Criticality Safety Benchmark Evaluation Project Handbook. The recent execution of the experiment aids in proper quantification of model simplifications and all uncertainties associated with the experiment. Historical benchmark evaluations are heavily relied on for uranium nuclear data validation despite the fact that the same level of documentation and comparable uncertainty analysis may not be present. The MUSIC evaluation is less likely to include “unknown unknowns” that could impede accurately modeling the system. Presented are both highly detailed and very simplified models, which represent the experimental configurations accurately, aiding the users of the benchmark for nuclear data or transport code validation. The sensitivities of k eff to nuclear data and nuclear data–related uncertainties are very similar between this experiment and previous bare uranium sphere experiments. In addition, the nuclear data uncertainties to any nuclides other than 235 U are small. For all these reasons, the recently evaluated MUSIC benchmark critical configurations could prove very useful for 235 U nuclear data validation. Currently, major libraries have good agreement with the experimental results, within 200 pcm for all nuclear data libraries, and within one standard deviation of the experimental result for most. Suggested nuclear data adjustments based on MUSIC and Lady Godiva are also presented, with posterior improvements to both the agreement in k eff and the uncertainty associated with the nuclear data.

A compact electron beam ion source for highly charged ion experiments at large-scale user facilities

Probing and manipulating of 2D materials and their heterostructures using slow highly charged ions (HCIs) is currently a hot topic due to the ultimate surface sensitivity of electronic sputtering with profound implications for fundamental research and technological applications. To study surface modifications without the complications of sample transport from ion irradiation to complex microscopic or spectroscopic analysis tools, the development of compact and thus portable ion sources is essential. In this paper we present the first results of the electron beam ion source-Compact version 1 (EBIS-C1), a novel and highly compact source for highly charged ions manufactured by D.I.S Germany GmbH. The main focus of this paper is to demonstrate the suitability of the EBIS-C1 as an ideal source for ion scattering experiments at surfaces and at gas/liquid jet targets by presenting the first charge state spectra of extracted neon, argon and xenon ions. The results highlight the potential of this portable EBIS to become a versatile platform for the study of HCI-surface interactions, allowing investigations to be carried out at user terminals in different laboratory environments.

Porous isoreticular non-metal organic frameworks

Metal–organic frameworks (MOFs) are useful synthetic materials that are built by the programmed assembly of metal nodes and organic linkers1. The success of MOFs results from the isoreticular principle2, which allows families of structurally analogous frameworks to be built in a predictable way. This relies on directional coordinate covalent bonding to define the framework geometry. However, isoreticular strategies do not translate to other common crystalline solids, such as organic salts3–5, in which the intermolecular ionic bonding is less directional. Here we show that chemical knowledge can be combined with computational crystal-structure prediction6 (CSP) to design porous organic ammonium halide salts that contain no metals. The nodes in these salt frameworks are tightly packed ionic clusters that direct the materials to crystallize in specific ways, as demonstrated by the presence of well-defined spikes of low-energy, low-density isoreticular structures on the predicted lattice energy landscapes7,8. These energy landscapes allow us to select combinations of cations and anions that will form thermodynamically stable, porous salt frameworks with channel sizes, functionalities and geometries that can be predicted a priori. Some of these porous salts adsorb molecular guests such as iodine in quantities that exceed those of most MOFs, and this could be useful for applications such as radio-iodine capture9–12. More generally, the synthesis of these salts is scalable, involving simple acid–base neutralization, and the strategy makes it possible to create a family of non-metal organic frameworks that combine high ionic charge density with permanent porosity.

Self-Assembly of Ionic Superdiscs in Nanopores.

Discotic ionic liquid crystals (DILCs) consist of self-assembled superdiscs of cations and anions that spontaneously stack in linear columns with high one-dimensional ionic and electronic charge mobility, making them prominent model systems for functional soft matter. Compared to classical nonionic discotic liquid crystals, many liquid crystalline structures with a combination of electronic and ionic conductivity have been reported, which are of interest for separation membranes, artificial ion/proton conducting membranes, and optoelectronics. Unfortunately, a homogeneous alignment of the DILCs on the macroscale is often not achievable, which significantly limits the applicability of DILCs. Infiltration into nanoporous solid scaffolds can, in principle, overcome this drawback. However, due to the experimental challenges to scrutinize liquid crystalline order in extreme spatial confinement, little is known about the structures of DILCs in nanopores. Here, we present temperature-dependent high-resolution optical birefringence measurement and 3D reciprocal space mapping based on synchrotron X-ray scattering to investigate the thermotropic phase behavior of dopamine-based ionic liquid crystals confined in cylindrical channels of 180 nm diameter in macroscopic anodic aluminum oxide membranes. As a function of the membranes' hydrophilicity and thus the molecular anchoring to the pore walls (edge-on or face-on) and the variation of the hydrophilic-hydrophobic balance between the aromatic cores and the alkyl side chain motifs of the superdiscs by tailored chemical synthesis, we find a particularly rich phase behavior, which is not present in the bulk state. It is governed by a complex interplay of liquid crystalline elastic energies (bending and splay deformations), polar interactions, and pure geometric confinement and includes textural transitions between radial and axial alignment of the columns with respect to the long nanochannel axis. Furthermore, confinement-induced continuous order formation is observed in contrast to discontinuous first-order phase transitions, which can be quantitatively described by Landau-de Gennes free energy models for liquid crystalline order transitions in confinement. Our observations suggest that the infiltration of DILCs into nanoporous solids allows tailoring their nanoscale texture and ion channel formation and thus their electrical and optical functionalities over an even wider range than in the bulk state in a homogeneous manner on the centimeter scale as controlled by the monolithic nanoporous scaffolds.

Numerical simulations on loss of ICRF-heated NBI ions in EAST

The loss of ion cyclotron resonance frequencies (ICRF)-heated neutral beam injection ions in experimental advanced superconducting tokamak was numerically investigated by ORBIT code simulations. The effects of collisions and ripples on particle losses were taken into account, and the distributions of fast ions generated by different beams in combination with ICRF heating were calculated using the TRANSP code. Results showed that ICRF waves altered the orbital distributions of beam ions, causing an increase in trapped ions and fast ion losses. Additionally, for co-current injected beams, perpendicular injection resulted in higher fast ion losses in synergistic heating than tangential injection. The study also found that the synergistic effect of collisions and ripples enhanced fast ion losses, which were highly localized and generated a maximum heat load of 0.165 MW m−2 on the first wall. However, conducting synergy heating experiments at high plasma currents and low effective ion charge numbers can significantly reduce the loss of fast ions.

Extraction experiments at the UNIST electron beam ion trap for highly charged ion studies

Highly charged ions (HCIs) are currently utilized in numerous fundamental and applied sciences, including astrophysics, dark matter search, optical clocks, semiconductor lithography, and quantum dot fabrication, to name just a few examples. At Ulsan National Institute of Science and Technology (UNIST), a tabletop electron beam ion trap (EBIT) has been developed for creating and studying HCIs. The UNIST-EBIT compresses the electron beam by 72 permanent magnets (up to 0.84 T) and produces up to He-like Ar ions. The primary objective of the UNIST-EBIT is to obtain X-ray spectrum data essential in astrophysics. Meanwhile, optical clocks based on HCIs are receiving significant attention from the scientific community. The UNIST-EBIT can also provide various HCIs for optical clock applications. For this purpose, designing an extraction beamline along with an initial extraction experiment of Ar ions from the EBIT is underway. To extract Ar ions, we consider constructing an automatic control system with EPICS. In this work, we present the recent progress of the UNIST-EBIT for extraction experiments.

A Long-life Laser Ion Source Using a Reproducible Solidified Gas Target

A novel laser ion source using a reproducible cryogenic target has been developed for next-generation heavy-ion cancer therapy accelerators. A solid thin layer of butane formed on a cylindrical cold head cooled with liquid nitrogen is ablated by a frequency-doubled Nd:YAG laser to generate high-charged carbon ions. The properties and reproducibility of the carbon plasmas produced under various conditions are investigated.

Experimental and theoretical Ritz–Rydberg analysis of the electronic structure of highly charged ions of lead and bismuth by optical spectroscopy

Intra-configuration fine-structure transitions in highly charged ions (HCIs) result in most cases from changes in the coupling of equivalent electrons. They are multipole forbidden to varying degrees and often occur within the optical range. In HCI with semi-filled nd and nf subshells, electrons can in principle couple to states which are energetically close but with very different total angular momenta, e.g. 0⩽J⩽10 . This gives rise to metastable states with very long lifetimes that exhibit particularly interesting clock transitions or, as in the case of orbital level crossings, acquire a considerable sensitivity to a possible variation of the fine-structure constant α. We investigate both experimentally and theoretically connecting the ground state and adjacent states of Pb XXII to Pb XXXIV and Bi X to Bi XV, respectively, covering complex couplings of electrons in the 4f and 5d shells. These and others such as nd and nf , which also contain equivalent electrons, are of interest for frequency metrology using quantum logic spectroscopy, for atomic structure and QED theory tests, and for the search for Dark Matter candidates. We infer their level structure, benchmark calculations from two different electronic structure codes, and lay the groundwork for inferring the wavelengths of forbidden transitions of higher multipolarity in the optical and VUV region.

Piezoionic Elastomers by Phase and Interface Engineering for High-Performance Energy-Harvesting Ionotronics.

Piezoionic materials play a pivotal role in energy-harvesting ionotronics. However, a persistent challenge lies in balancing the structural requirements for voltage generation, current conduction, and mechanical adaptability. The conventional approach of employing crystalline heterostructures for stress concentration and localized charge separation, while effective for voltage generation, often compromises the stretchability and long-range charge transport found in homogeneous quasisolid states. Herein, phase and interface engineering strategy is introduced to address this dilemma and a piezoionic elastomer is presented that seamlessly integrates ionic liquids and ionic plastic crystals, forming a finely tuned microphase-separated structure with an intermediate phase. This approach promotes charge separation via stress concentration among hard phases while leveraging the high ionic charge mobility in soft and intermediate phases. Impressively, the elastomer achieves an extraordinary piezoionic coefficient of about 6.0mV kPa-1, a more than threefold improvement over current hydrogels and ionogels. The resulting power density of 1.3 µW cm-3 sets a new benchmark, exceeding that of state-of-the-art piezoionic gels. Notably, this elastomer combines outstanding stretchability, remarkable toughness, and rapid self-healing capability, underscoring its potential for real-world applications. This work may represent a stride toward mechanically robust energy harvesting systems and provide insights into ionotronic systems for human-machine interaction.

DNA break clustering as a predictor of cell death across various radiation qualities: influence of cell size, cell asymmetry, and beam orientation

Abstract Cosmic radiation, composed of high charge and energy (HZE) particles, causes cellular DNA damage that can result in cell death or mutation that can evolve into cancer. In this work, a cell death model is applied to several cell lines exposed to HZE ions spanning a broad range of linear energy transfer (LET) values. We hypothesize that chromatin movement leads to the clustering of multiple double strand breaks (DSB) within one radiation-induced foci (RIF). The survival probability of a cell population is determined by averaging the survival probabilities of individual cells, which is function of the number of pairwise DSB interactions within RIF. The simulation code RITCARD was used to compute DSB. Two clustering approaches were applied to determine the number of RIF per cell. RITCARD outputs were combined with experimental data from four normal human cell lines to derive the model parameters and expand its predictions in response to ions with LET ranging from ~0.2 keV/μm to ~3000 keV/μm. Spherical and ellipsoidal nuclear shapes and two ion beam orientations were modeled to assess the impact of geometrical properties on cell death. The calculated average number of RIF per cell reproduces the saturation trend for high doses and high-LET values that is usually experimentally observed. The cell survival model generates the recognizable bell shape of LET dependence for the relative biological effectiveness (RBE). At low LET, smaller nuclei have lower survival due to increased DNA density and DSB clustering. At high LET, nuclei with a smaller irradiation area—either because of a smaller size or a change in beam orientation—have a higher survival rate due to a change in the distribution of DSB/RIF per cell. If confirmed experimentally, the geometric characteristics of cells would become a significant factor in predicting radiation-induced biological effects. Insight Box: High-charge and energy (HZE) ions are characterized by dense linear energy transfer (LET) that induce unique spatial distributions of DNA damage in cell nuclei that result in a greater biological effect than sparsely ionizing radiation like X-rays. HZE ions are a prominent component of galactic cosmic ray exposure during human spaceflight and specific ions are being used for radiotherapy. Here, we model DNA damage clustering at sub-micrometer scale to predict cell survival. The model is in good agreement with experimental data for a broad range of LET. Notably, the model indicates that nuclear geometry and ion beam orientation affect DNA damage clustering, which reveals their possible role in mediating cell radiosensitivity.

Precision measurement of M1 optical clock transition in Ni12+

Highly charged ions (HCIs) have drawn significant interest in quantum metrology and in the search for new physics. Among these, Ni12+ is considered as one of the most promising candidates for the next generation of HCI optical clocks, due to its two E1-forbidden transitions M1 and E2, which occur in the visible spectral range. In this work, we used the Shanghai-Wuhan electron beam ion trap to perform a high-precision measurement of the M1 transition wavelength. Our approach involved an improved calibration scheme for the spectra, utilizing auxiliary Ar+ lines for calibration and correction. Our final measured result of the M1 transition wavelength demonstrates a fivefold improvement in accuracy compared to our previous findings, reaching the subpicometer level accuracy. In combination with our rigorous atomic-structure calculations to capture the electron correlations and relativistic effects, the quantum electrodynamic corrections were extracted. Published by the American Physical Society 2024

Two-body fragmentation of methane induced by extreme ultraviolet and high charge ions

CH<sub>4</sub> is abundant in planetary atmosphere, and the study of CH<sub>4</sub> dissociation dynamics is of great importance and can help to understand the atmospheric evolution process in the universe. At present, the <inline-formula><tex-math id="M6">\begin{document}$ {\text{CH}}_4^{2 + } \to {\text{CH}}_3^ + + {{\text{H}}^ + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M6.png"/></alternatives></inline-formula> channel has been extensively studied, but the explanation of the dissociation mechanism for this channel is controversial. In this work, the double-photoionization experiment of CH<sub>4</sub> by extreme ultraviolet photon (XUV) in an energy range of 25－44 eV and the collision experiment between 1 MeV Ne<sup>8+</sup> and CH<sub>4</sub> are carried out by using the reaction microscope. The three-dimensional (3D) momenta of <inline-formula><tex-math id="M7">\begin{document}$ {\text{CH}}_3^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M7.png"/></alternatives></inline-formula> and H<sup>+</sup> ions are measured in coincidence, and the corresponding kinetic energy release (KER) is reconstructed, and fragmentation dynamics from the parent ion <inline-formula><tex-math id="M8">\begin{document}$ {\text{CH}}_4^{2 + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M8.png"/></alternatives></inline-formula> to the <inline-formula><tex-math id="M9">\begin{document}$ {\text{CH}}_3^ + + {{\text{H}}^ + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M9.png"/></alternatives></inline-formula> ion pair are investigated. In the photoionization experiment, two peaks in the KER spectrum are observed: one is located around 4.75 eV, and the other lies at 6.09 eV. Following the conclusions of previous experiments and the theoretical calculations of Williams et al. (Williams J B, Trevisan C S, Schöffler M S, Jahnke T, Bocharova I, Kim H, Ulrich B, Wallauer R, Sturm F, Rescigno T N, Belkacem A, Dörner R, Weber T, McCurdy C W, Landers A L 2012 <i>J. Phys. B At. Mol. Opt. Phys.</i> <b>45</b> 194003), we discuss the corresponding mechanism of each KER peak. For the 6.09 eV peak, we attribute it to the <inline-formula><tex-math id="M10">\begin{document}$ {\text{CH}}_4^{2 + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M10.png"/></alternatives></inline-formula> dissociation caused by the Jahn-Teller effect, because this value is consistent with the energy difference in energy between the <inline-formula><tex-math id="M11">\begin{document}$ {\text{CH}}_4^{2 + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M11.png"/></alternatives></inline-formula> <sup>1</sup>E initial state and the <inline-formula><tex-math id="M12">\begin{document}$ {\text{CH}}_3^ + /{{\text{H}}^ + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M12.png"/></alternatives></inline-formula> final state involving the Jahn-Teller effect. For the 4.75 eV peak, we believe that it may come from the direct dissociation of <inline-formula><tex-math id="M13">\begin{document}$ {\text{CH}}_4^{2 + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M13.png"/></alternatives></inline-formula> without contribution from the Jahn-Teller effect. More specifically, Williams et al. presented the potential energy curve for one C-H bond stretching to 8 a.u., while other C—H bonds are fixed at the initial geometry of the CH<sub>4</sub> molecule. In the reflection approximation, we infer that the extra energy is released from the internuclear distance of 8 a.u. to infinity. It is found that the KER is 4.7 eV, which is consistent with the experimental observation, suggesting that the KER peak at 4.75 eV may arise from the direct dissociation of <inline-formula><tex-math id="M14">\begin{document}$ {\text{CH}}_4^{2 + } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231377_M14.png"/></alternatives></inline-formula> without contribution from the Jahn-Teller effect. In addition, in the 1 MeV Ne<sup>8+</sup> ion collision experiment, it is observed that the released energy values corresponding to the three KER peaks are about 4.65, 5.75, and 7.94 eV. By comparing the branching ratio of each peak with the previous experimental result, it is suggested that the velocity effect is not significant in KER spectra.

Two-body fragmentation of methane induced by extreme ultraviolet and high charge ions

CH<sub>4</sub> is abundant in planetary atmospheres, and the study of CH<sub>4</sub> dissociation dynamics is of great importance and can help to understand the atmospheric evolution process in the universe. At present, the CH<sub>4</sub><sup>2+</sup>→ CH<sub>3</sub><sup>+</sup>+H<sup>+</sup> channel has been extensively studied, but the explanation of the dissociation mechanism for this channel is controversial. In this work, the double-photoionization experiment of CH<sub>4</sub> by extreme ultraviolet photon (XUV) in the energy range of 25-44 eV and the collision experiment between 1 MeV Ne<sup>8+</sup> and CH<sub>4</sub> were carried out on the reaction microscope. The 3D momenta of CH<sub>3</sub><sup>+</sup> and H<sup>+</sup> ions were measured in coincidence, the corresponding kinetic energy release (KER) was reconstructed, and fragmentation dynamics from the parent ion CH<sub>4</sub><sup>2+</sup> to the CH<sub>3</sub><sup>+</sup>+H<sup>+</sup> ion pair were investigated. In the photoionization experiment, we observed two peaks in the KER spectrum, one locates around 4.75 eV, and the other one lies at 6.09 eV. Benefiting from the conclusions of previous experiments and the theoretical calculations of Williams [19] et al, we discussed the corresponding mechanism of each KER peak. For the 6.09 eV peak, we attributed it to the CH<sub>4</sub><sup>2+</sup> dissociation mediated by the Jahn-Teller effect, as this value is consistent with the energy difference between the CH<sub>4</sub><sup>2+</sup> <sup>1</sup>E initial state and the CH<sub>3</sub><sup>+</sup> /H+ final state involving the Jahn-Teller effect. For the 4.75 eV peak, we proposed that it may come from the direct dissociation of CH<sub>4</sub><sup>2+</sup> without the Jahn-Teller effect. In more detail, Williams<sup>[19]</sup> et al presented the potential energy curve for one C-H bond stretching to 8 a.u., while other C-H bonds are fixed at the initial geometry of the CH<sub>4</sub> molecule. Based on the reflection approximation, we deduced the additional energy release from the internuclear distance of 8 a.u. to infinity. We found the sum KER is 4.7 eV, this is consistent with the experimental observation and suggests that the KER peak at 4.75 eV may arise from the direct dissociation of CH<sub>4</sub><sup>2+</sup> without the Jahn-Teller effect. In addition, in the 1 MeV Ne<sup>8+</sup> ion collision experiment, we observed three KER peaks with the mean kinetic energy release values of around 4.65, 5.75, and 7.94 eV. By comparing the branching ratio of each peak with the previous experimental results, it is suggested that the velocity effect is not significant in KER spectra.

Experimental and theoretical research progress of <sup>2</sup>P<sub>1/2 </sub> – <sup>2</sup>P<sub>3/2</sub> transitions of highly charged boron-like ions

The precise measurement of the fine structure and radiative transition properties of highly charged ions (HCI) is essential for testing fundamental physical models, including strong-field quantum electrodynamics (QED) effects, electron correlation effects, relativistic effects, and nuclear effects. These measurements also provide critical atomic physics parameters for astrophysics and fusion plasma physics. Compared with the extensively studied hydrogen-like and lithium-like ion systems, boron-like ions exhibit significant contributions in terms of relativistic and QED effects in their fine structure forbidden transitions. High-precision experimental measurements and theoretical calculations of these systems provide important avenues for further testing fundamental physical models in multi-electron systems. Additionally, boron-like ions are considered promising candidates for HCI optical clocks. This paper presents the latest advancements in experimental and theoretical research on the ground state <sup>2</sup>P<sub>3/2</sub>—<sup>2</sup>P<sub>1/2</sub> transition in boron-like ions, and summarizes the current understanding of their fine and hyperfine structures. It also discusses a proposed experimental setup for measuring the hyperfine splitting of boron-like ions by using an electron beam ion trap combined with high-resolution spectroscopy. This proposal aims to provide a reference for future experimental research on the hyperfine splitting of boron-like ions, to test the QED effects with higher precision, extract the radius of nuclear magnetization distribution, and validate relevant nuclear structure models.

Precise measurements of electron <i>g</i> factors in bound states of few-electron ions

<sec>The electron <i>g</i> factor is an important fundamental structural parameter in atomic physics, as it reveals various mechanisms of interactions between electrons and external fields. Precise measurements of <i>g</i> factors of bound electrons in simple atomic and molecular systems provide an effective method for investigating the bound-state quantum electrodynamics (QED) theory. Especially in highly-charged heavy ions (HCIs), the strong electromagnetic interactions between the nuclei and inner-shell electrons provide unique opportunities to test QED under extremely strong fields. Accurate measurements of the <i>g</i> factors of the bound-state electrons are also important for determining nuclear effects, nuclear parameters and fundamental constants. The research on <i>g</i> factors of the bound-state electrons has become a frontier topic in fundamental physics. A Penning trap, which uses steady-state electromagnetic fields to confine charged particles, is utilized to precisely measure the <i>g</i> factor. This paper presents a comprehensive review of the experiments on <i>g</i> factors for few-electron simple systems in Penning traps, including experimental principles, experimental setups, measurement methods, and a summary of important research findings. The physical concept of the electron <i>g</i> factor and its historical research background are introduced. The electron <i>g</i> factor is considered as an effective probe to study higher-order QED effects. Through high-precision measurements of the free electron g factor, discrepancies between the fine-structure constants and other experimental results in atomic physics are identified. Notably, the <i>g</i> factor of the 1s electron in HCIs deviates significantly from the value for free electrons as the atomic number increases. Experimental principles, including the principle of the Penning trap and the principle of measuring the bound-state electron <i>g</i> factors are discussed. A double-trap experiment setup and related precision measurement techniques are also introduced.</sec><sec>This paper reviews several milestone experiments including (1) the stringent test of bound-state QED by precise measurement of bound-state electron <i>g</i> factor of a <sup>118</sup>Sn<sup>49+</sup> ion, (2) measurement of the <i>g</i> factors of lithium-like and boron-like ions and their applications, and (3) measurement of the <i>g</i>-factor isotope shift by using an advanced two-ion balance technique in the Penning trap, providing an insight into the QED effects in nuclear recoil. Finally, this paper summarizes the challenges currently faced in measuring the <i>g</i> factors of bound-state electrons in few-electron ion systems and provides the prospects for the future developments of this field.</sec>

State-selective charge exchange cross sections in collisions of highly-charged sulfur ions with helium and molecular hydrogen

The state-selective cross section data are useful for understanding and modeling the x-ray emission in celestial observations. In the present work, using the cold target recoil ion momentum spectroscopy, for the first time we investigated the state-selective single electron capture processes for S q+–He and H2 (q = 11–15) collision systems at an impact energy of q × 20 keV and obtained the relative state-selective cross sections. The results indicate that only a few principal quantum states of the projectile energy level are populated in a single electron capture process. In particular, the increase of the projectile charge state leads to the population of the states with higher principal quantum numbers. It is also shown that the experimental averaged n-shell populations are reproduced well by the over-barrier model. The database is openly available in Science Data Bank at 10.57760/sciencedb.j00113.00091.

Hybrid nanoarchitectonics of ordered mesoporous C60–BCN with high surface area for supercapacitors and lithium-ion batteries

Mesoporous materials have shown immense potential for their use in energy storage applications due to their unique pore structural features and high surface areas. There is an immense interest in developing high performance electrode materials for the next generation energy storage devices. In this work, ordered mesoporous hybrids of fullerene and borocarbonitride with a high surface area are synthesized using KIT-6 as a hard template. The high surface area and uniform pore size distribution of the hybrids decorated with C60 nanostructures accounted for a high ion charge transfer which led to increased electrochemical stability. The optimized material exhibits exceptional supercapacitance stability of ∼100 % after 6000 cycles at 5 A g−1, with a capacitance of 171.2 F g−1 at 0.5 A g−1. The material is also used as anodes in lithium-ion batteries wherein it displays exceptional capacitance retention, storage capacity, coulombic efficiency, and rate capability. The storage capacity of the anode material is found to be 1268.3/1164.9/443.8 mA h g−1 at 0.05/0.1/1 A g−1. The ordered mesoporosity, high surface area, and functionalized surface along with the intermolecular electron transfer enabled due to C60 offers exciting prospects for the material to be used as novel electrode materials.

Simultaneous observation of noble gases and highly charged ions in an electron beam ion trap for accurate wavelength calibration of optical transitions

Spectral lines of buffer noble gases injected into an electron beam ion trap (EBIT) have recently been used as a reference to aid accurate determination of the wavelengths of optical transitions of highly charged ions (HCIs). Simultaneous observation of emission lines of HCIs along with those of neutral atoms or singly charged ions represents a reliable method for wavelength calibration that suppresses systematic uncertainties. Here, we present visible and infrared emission spectra of buffer Ne and Ar gases in an EBIT and briefly review the buffer gas calibration method. The experimental conditions required for implementing the calibration method are discussed by investigating the dependence of the emission spectra of mixtures of HCIs and noble gases on electron beam’s parameters and gas pressure.

Sympathetically cooled highly charged ions in a radio-frequency trap with superconducting magnetic shielding

We sympathetically cool highly charged ions (HCI) in Coulomb crystals of Doppler-cooled Be+ ions confined in a cryogenic linear Paul trap that is integrated into a fully enclosing radio-frequency resonator manufactured from superconducting niobium. By preparing a single Be+ cooling ion and a single HCI, quantum logic spectroscopy toward frequency metrology and qubit operations with a great variety of species are enabled. While cooling down the assembly through its transition temperature into the superconducting state, an applied quantization magnetic field becomes persistent, and the trap becomes shielded from subsequent external electromagnetic fluctuations. Using a magnetically sensitive hyperfine transition of Be+ as a qubit, we measure the fractional decay rate of the stored magnetic field to be at the 10−10 s−1 level. Ramsey interferometry and spin-echo measurements yield coherence times of >400 ms, demonstrating excellent passive magnetic shielding at frequencies down to DC.