Highly Charged Ions Research Articles

Evidence of a new phase in gypsum-anhydrite transformations under microwave heating by in situ dielectric analysis and Raman spectroscopy.

Mineral transformations of the gypsum-anhydrite system under microwave heating have been studied using in situ dielectric thermal analysis (MW-DETA) and Raman spectroscopy simultaneously. The dielectric properties of samples that were measured under microwave heating provided thorough information about the dynamics of the gypsum-anhydrite system transformations and its significance from the mineralogical point of view. In particular, the MW-DETA technique revealed a new intermediate phase with a γ-anhydrite structure. This phase corresponds to the soluble stage of γ-anhydrite, and it is characterized by a high ionic charge inside the crystal channels. The complete sequence is gypsum → 0.625-subhydrate → bassanite → hydro γ-anhydrite → anhydrous γ-anhydrite → β-anhydrite. The transformations were also assessed using DSC, TG, DTA and dielectric measurements at room temperature, as well as other techniques including X-ray powder diffraction (XRPD) and high-temperature XRD (HT-XRD). Correlations between the dielectric properties with temperature and the rest of the techniques elucidated the heating mechanisms of this material under microwave energy during the different stages. The in situ combination of the MW-DETA and the Raman analysis appears to be a powerful technique, providing new insights about the mechanisms which govern the volumetric heating of this and other materials.

Towards background-free studies of capture reactions in a heavy-ion storage ring

SynopsisStored and cooled highly-charged ions offer unprecedented capabilities for precision studies in realm of atomic-, nuclear-structure and astrophysics. In context of the latter, after the successful investigation of the cross section of 96Ru(p,γ) in 2009, in 2016 the first measurement of the 124Xe(p,γ)125Cs reaction was performed at the Experimental Storage Ring (ESR) at GSI.

Novel “Ionology Art for Art Ionology Methods” in 4π plasma focus device space: Bridging art, science and technology

Novel “Ionology Art for Art Ionology (IAAI) Methods” were invented by us and presented for the first time in this paper by successfully bridging art, science and technology for producing “Positive and Negative Art Ionograms” or “Art Ion Shadowgrams” using 4π ion beams of a plasma focus device (PFD). As recently discovered by us, a PFD emits 4π high intensity heavy charged ions isotropically in PFD space which was used for the first time in this study for producing “Art Ionograms” which is a wide-scale wide-angle application. Art patterns to be ionographed were transferred and cut on vinyl decal sheet which was stuck onto a panorama polycarbonate ion image detector, and then bombarded by helium ions in 4π PFD space in order to form “Hidden Art Patterns”. The polycarbonate detectors with “Hidden Art Patterns” have been developed in panorama single-cell mega-size electrochemical ion image processing systems. High resolution “Art Ionograms” such as thin flat art patterns, poems and even portraits were produced, sharply observed by the unaided eyes and framed as beautiful art pieces. This study while introduced novel “IAAI Methods” by using full-scale 4π PFD ion beams, it also demonstrated how scientifically and efficiently ion beams in 4π PFD space can be used for large-scale wide-angle applications with a high prospect for applications in medicine, industry, science and technology. On the other hand, it is hoped that the novel inventions made, the unique framed art pieces produced as presented here and those being further produced for setting up a “Gallery of Particle-bombarded Arts” are remained as a worldwide cultural heritage of bridged art, science and technology.

Production of highly charged ions of rare species by laser-induced desorption inside an electron beam ion trap.

This paper reports on the development and testing of a novel, highly efficient technique for the injection of very rare species into electron beam ion traps (EBITs) for the production of highly charged ions (HCI). It relies on in-trap laser-induced desorption of atoms from a sample brought very close to the electron beam resulting in a very high capture efficiency in the EBIT. We have demonstrated a steady production of HCI of the stable isotope 165Ho from samples of only 1012 atoms (∼300 pg) in charge states up to 45+. HCI of these species can be subsequently extracted for use in other experiments or stored in the trapping volume of the EBIT for spectroscopic measurements. The high efficiency of this technique extends the range of rare isotope HCIs available for high-precision atomic mass and spectroscopic measurements. A first application of this technique is the production of HCI of the synthetic radioisotope 163Ho for a high-precision measurement of the QEC-value of the electron capture in 163Ho within the "Electron Capture in Holmium" experiment [L. Gastaldo et al., J. Low Temp. Phys. 176, 876-884 (2014); L. Gastaldo et al., Eur. Phys. J.: Spec. Top. 226, 1623-1694 (2017)] (ECHo collaboration) ultimately leading to a measurement of the electron neutrino mass with an uncertainty on the sub electronvolt level.

Single-site magnetic anisotropy governed by interlayer cation charge imbalance in triangular-lattice AYbX2

The behavior in magnetic field of a paramagnetic center is characterized by its $g$ tensor. An anisotropic form of the latter implies different kind of response along different crystallographic directions. Here we shed light on the anisotropy of the $g$ tensor of Yb$^{3+}$ 4$f^{13}$ ions in NaYbS$_2$ and NaYbO$_2$, layered triangular-lattice materials suggested to host spin-liquid ground states. Using quantum chemical calculations we show that, even if the ligand-cage trigonal distortions are significant in these compounds, the crucial role in realizing strongly anisotropic, `noncubic' $g$ factors is played by inter-layer cation charge imbalance effects. The latter refer to the asymmetry experienced by a given Yb center due to having higher ionic charges at adjacent metal sites within the magnetic $ab$ layer, i.e., 3+ nearest neighbors within the ab plane versus 1+ species between the magnetic layers. According to our results, this should be a rather general feature of 4$f^{13}$ layered compounds: less inter-layer positive charge is associated with stronger in-plane magnetic response.

Laser ablation plasma with solenoid field confinement.

A Laser Ion Source (LIS) can produce high charge state and high intensity ion beams (∼emA), especially, refractory metallic ion beams, which makes it a promising candidate as an ion source for heavy ion cancer therapy facilities and future accelerator complexes, where pulsed high intensity and high charged heavy ion beams are required. However, it is difficult for the LIS to obtain a long pulse width while ensuring high current intensity, thus limiting the application of the LIS. To solve the conflict, magnetic fields are proposed to confine the expansion of the laser produced plasma. With a solenoid along the normal direction to the target surface, the lateral adiabatic expansion of the laser ablation plasma is suppressed which extends the pulse width of the ion beam effectively. The characteristics of laser ablation plasma with solenoid field confinement will be presented and discussed in this paper.

Charge-Exchange-Driven Low-Energy Electron Splash Induced by Heavy Ion Impact on Condensed Matter.

Low-energy electrons (LEEs) are of great relevance for ion-induced radiation damage in cells and genes. We show that charge exchange of ions leads to LEE emission upon impact on condensed matter. By using a graphene monolayer as a simple model system for condensed organic matter and utilizing slow highly charged ions (HCIs) as projectiles, we highlight the importance of charge exchange alone for LEE emission. We find a large number of ejected electrons resulting from individual ion impacts (up to 80 electrons/ion for Xe40+). More than 90% of emitted electrons have energies well below 15 eV. This "splash" of low-energy electrons is interpreted as the consequence of ion deexcitation via an interatomic Coulombic decay (ICD) process.

Biomimetic Nanocones that Enable High Ion Permselectivity.

Artificial counterparts of conical-shaped transmembrane protein channels are of interest in biomedical sciences for biomolecule detection and selective ion permeation based on ionic size and/or charge differences. However, industrial-scale applications such as seawater desalination, separation of mono- from divalent cations, and treatment of highly-saline industrial waste effluents are still big challenges for such biomimetic channels. A simple monomer seeding experimental approach is used to grow ionically conductive biomimetic charged nanocone pores at the surface of an acid-functionalized membrane. These readily scalable nanocone membranes enable ultra-fast cation permeation (Na+ =8.4× vs. Mg2+ =1.4×) and high ion charge selectivity (Na+ /Mg2+ =6×) compared to the commercial state-of-the-art permselective membrane (CSO, Selemion, Japan) owing to negligible surface resistance and positively charged conical pore walls.

Biomimetic Nanocones that Enable High Ion Permselectivity

AbstractArtificial counterparts of conical‐shaped transmembrane protein channels are of interest in biomedical sciences for biomolecule detection and selective ion permeation based on ionic size and/or charge differences. However, industrial‐scale applications such as seawater desalination, separation of mono‐ from divalent cations, and treatment of highly‐saline industrial waste effluents are still big challenges for such biomimetic channels. A simple monomer seeding experimental approach is used to grow ionically conductive biomimetic charged nanocone pores at the surface of an acid‐functionalized membrane. These readily scalable nanocone membranes enable ultra‐fast cation permeation (Na+=8.4× vs. Mg2+=1.4×) and high ion charge selectivity (Na+/Mg2+=6×) compared to the commercial state‐of‐the‐art permselective membrane (CSO, Selemion, Japan) owing to negligible surface resistance and positively charged conical pore walls.

Development of the HITRAP cooling trap and the EBIT offline ion source

HITRAP is a facility for deceleration of highly charged ions (HCI) produced online by the GSI accelerator. It consists of two linear stages for deceleration down to several keV/charge and an ion trap for ion cooling down to sub-eV energies. We report on two recent developments within the facility: a new design for the HITRAP cooling trap in order to improve its stability and voltage rigidity, as well as the investigation of the so-called MIVOC method in the HITRAP EBIT for production of Sb35+, Fe21+, and B5+.

Classical-trajectory Monte Carlo calculations of differential electron-emission cross sections in fast heavy-ion collisions with water molecules

A classical description of electron emission differential ionization cross sections for highly-charged high-velocity ions ($\sim$ 10 a.u.) impinging on water molecules is presented. We investigate the validity of the classical statistical mechanics description of ionization ($\hbar=0$ limit of quantum mechanics) in different ranges of electron emission energy and solid angle, where mechanisms such as soft and binary collisions are expected to contribute. The classical-trajectory Monte Carlo method is employed to calculate doubly and singly differential cross sections for C$^{6+}$, O$^{8+}$ and Si$^{13+}$ projectiles, and comparisons with Continuum Distorted Wave Eikonal Initial State theoretical results and with experimental data are presented. We implement a time-dependent screening effect in our model, in the spirit of mean-field theory to investigate its effect for highly charged projectiles. We also focus on the role of an accurate description of the molecular target by means of a three-center potential to show its effect on differential cross sections. Very good agreement with experiments is found at medium to high electron emission energies.

Interaction of highly charged ions with carbon‐based materials using Kobe EBIS

Interaction of highly charged ions (HCIs) with surfaces produce various specific phenomena as a consequence of the potential energy that HCI possesses. In the present study, we have observed photon emission, structural, magnetic, and electronic modification on various carbon‐based materials such as carbon nanotube by the impact of HCIs using an electron beam ion source named Kobe EBIS installed at the Kobe University. In order to study the potential effect, HCIs of Arq+ (q = 6–16) with the intensity of 0.1–1 nA are projected on the surface with a constant kinetic energy (16 keV). For photon emission measurements, we observed spatial and spectral distribution of visible light emission from the surface during irradiation with HCIs. On the other hand, the structural modification of multi‐walled carbon nanotubes (MWCNTs) irradiated with HCIs has been analyzed using a transmission electron microscopy and Raman spectroscopy. Irradiation effects on the resistivity of single MWCNT supported on micrometer scale bridge pattern were also measured. We have also measured magnetic structure of highly oriented pyrolytic graphite irradiated with HCIs using electron spin resonance at low temperature. At the present paper, we will review our recent experimental results on the interaction of HCI with various carbon‐based materials.

Characteristics of highly charged ions produced at Kobe EBIS under modulated operation

The electron beam ion source (Kobe EBIS) has been developed to perform modification of surfaces using highly charged ions (HCIs) at the Kobe University, Japan. Recent study revealed that periodic intermission of electron beam improves charge state distribution of extracted ions. The period of intermission is in the order of 100 ms, and the width of beam‐off time is 1 ms or less. This operational mode (pulse mode) makes it possible to produce Ar15+ to Ar17+ effectively, whereas the charge is limited less than 14+ under the ordinary operational mode with direct current (DC) electron beam. A spike of HCIs with a peak current in the order of nA is also observed at each moment of electron beam off. The measurement of the time evolution of Ar16+ intensity around the timing of mode change revealed that the intensity of extracted Ar16+ changes slowly after mode change with a time constant of few seconds.

Dissociative ionization of the H2O molecule bombarded by swift singly charged and slow highly charged ions

Fragment ion energy spectra of the water molecule have been measured in conventional crossed‐beam experiments by the impact of 46 keV/u energy, singly charged ions (SCIs) and 4.3 keV/u energy, highly charged ions (HCIs). Double differential cross sections have been determined and a comparative analysis has been performed. We found that the fragmentation spectra for SCIs and HCIs are very similar, indicating that both collisions lead to the same fragmentation channels. This suggests that the Coulomb explosion of the water molecule is dominantly determined by the charge state of the transient molecular ions, and it is almost independent from the primary ionization mechanism. Differences were observed not only between the SCI and HCI impact‐induced fragmentation cross sections, but between those obtained by the 60 keV N6+ and 70 keV O7+ projectiles. The differences were attributed to the selectivity of the electron capture process for HCIs. Multiple target ionization cross sections have been deduced from the fragment ion spectra. We found contributions of up to fivefold ionization for SCIs and up to sixfold ionization for HCIs.

Off-axis electron injection into a cooler Penning trap

The TITAN facility at TRIUMF is a series of ion traps designed for precision mass spectrometry on rare isotopes. The combination of an on-line electron beam ion trap charge breeder with a Penning trap enables measurements with radioactive ions in high charge states. The use of highly charged ions (HCI) can yield a significant gain in mass precision and mass resolving power. However, the benefits of high charge states are mitigated since the charge breeding deteriorates the beam quality. To achieve suitable beam properties and access the full potential of Penning trap mass spectrometry with HCI a cooler Penning trap (CPET) for electron cooling of highly charged radioisotopes is being developed. In this device short-lived HCI will be sympathetically cooled by a co-trapped electron plasma prior to mass measurement. For electron plasma generation electrons are injected from an off-axis electron gun placed in the fringe field of CPET’s solenoid magnet. We report on the development of an electron gun design that is adapted to the operation in lateral magnetic fields and has enabled efficient and robust electron plasma formation in CPET.

Potential effect in Balmer light emission near surface irradiated with highly charged ions

The interaction between highly charged ions (HCIs) and the solid surface causes various phenomena due to high potential energy of HCIs. Luminescence is also included in them. In order to investigate the origin of the light emission from the surface irradiated with HCIs, we conducted spectroscopic measurements and then we investigated characteristics of Balmer light emission because potential effect of HCI was remarkable in Balmer light emitted from hydrogen atoms desorbed from the surface. In the present study, the Balmer light intensity was revealed to increase rapidly with the charge state of HCIs.

Possible Cool Prominence Materials Detected within Interplanetary Small Magnetic Flux Ropes

Abstract Previous studies indicate that interplanetary small magnetic flux ropes (SMFRs) are manifestations of microflare-associated small coronal mass ejections (CMEs), and the hot material with high-charge states heated by related microflares are found in SMFRs. Ordinary CMEs are frequently associated with prominence eruptions, and cool prominence materials are found within some magnetic clouds (MCs). Therefore, the predicted small CMEs may also be frequently associated with small prominence eruptions. In this work, we aim to search for cool prominence materials within SMFRs. We examined all the O5+ and Fe6+ fraction data obtained by the Advanced Composition Explorer (ACE) spacecraft during 1998–2008 and found that 13 SMFRs might exhibit low-charge-state signatures of unusual O5+ and/or Fe6+ abundances. One of the 13 SMFRs also exhibited signatures of high ionic charge states. We also reported a SMFR with high Fe6+ fraction, but the values of Fe6+ is a little lower than the threshold defining unusual Fe6+. However, the Solar Dynamics Observatory/ Atmospheric Imaging Assembly observations confirmed that the progenitor CME of this SMFR is associated with a small eruptive prominence, and the observations also supported the prominence materials were embedded in the CME. These observations are at the edge of the capabilities of ACE/Solar Wind Ion Composition Spectrometer and it cannot be ruled out that they are solely caused by instrumental effects. If these observations are real, they provide new evidence for the conjecture that SMFRs are small-scale MCs but also imply that the connected small CMEs could be associated with flares and prominence eruptions.

Ab initio dielectronic recombination rate coefficients for highly-charged Ar-like ions

Employing the independent-processes isolated-resonance distorted-wave approximation, we have made a comprehensive study on dielectronic recombination (DR) for 19 highly-charged Ar-like ions with nuclear charge number Z=23–30, 36, 42, 50, 54, 60, 64, 70, 74, 79, 85 and 92. For the convenience of usage, the ab initio level-by-level total rate coefficients for DR initially from both the ground state 3s23p6 1S0 and the metastable state 3s23p53d 3P0 are presented in a simple compact fitting form. We include the 3 → 3 (Δn=0), 2 → 3 and 3 → 4 (Δn=1), and 3 → 5 (Δn=2) core-excitations resonances as well as the decays from the resonances toward low-lying autoionizing levels followed possibly by radiative cascade effects in our ab initio DR results. The detailed configuration interaction analysis and comparisons with both theoretical and experimental results show that present total DR rate coefficients are reliable at both low (with a typical uncertainty of a factor of 2 in the photoionized plasma zone) and high (with an uncertainty of about 20% in the collisional plasma zone) temperature. To our knowledge, these are the first ab initio DR results for most of ions with Z > 30.

Atomic kinetics calculations of complex highly-charged ions in plasmas in non-local thermodynamic equilibrium by using a Monte-Carlo approach

A new calculation of atomic kinetics of multiple-charged tungsten ions in a high temperature plasma in the non-local thermodynamic equilibrium (nLTE) based on the Markov chain Monte-Carlo (MCMC) method is presented. It is shown that the fractional ion abundance and the resulting mean charge of the plasma can be calculated with much lower computational time compared to conventional methods. The present method can be easily parallelized and is applicable to larger problems, such as modeling coupled atomic processes and radiation hydrodynamics.

Vacuum requirements for Penning trap mass spectrometry with highly charged ions

Experimental investigations employing highly charged ions (HCI) typically require very strict vacuum quality. In Penning trap mass spectrometry (PTMS), HCI can significantly improve the precision and resolution of mass measurements, but they are also subject to charge-exchange reactions with neutral gas particles, which may hamper the quality of the measurement. In this study, we employed a simple method to determine that the maximum pressure levels required for an undisturbed PTMS measurement of HCI is on the order of 10-11 mbar. We also evaluate the residual gas pressure in the Penning trap mass spectrometer at TITAN facility by measuring the rate of charge-exchange reactions with HCI, revealing that the trap’s vacuum must be improved in about two orders of magnitude to reach the desired level.