Ion Charge State Research Articles

An alternative justification for the stationary assumption made by many reduced models for nonlocal electron heat flow in plasmas

Nonlocal models are widely used for approximating kinetic effects on electron heat flow in fusion-relevant plasmas. Almost universally, such models have no explicit time dependence and are designed to make heat flow predictions based directly on instantaneous profiles of macroscopic plasma parameters. While this is usually justified by the claim that transient effects fade before temperature profiles evolve appreciably, a more rigorous justification of the stationarity assumption in terms of kinetic theory is desirable. In this Letter, such a justification is provided by demonstrating that nonstationary effects related to the time dependence of the isotropic part of the electron distribution function vanish up to third order in Chapman–Enskog theory (irrespective of ion charge state or presence of magnetic fields). However, it is found that the electron inertia term (whose appearance in Ohm's law stems from the time derivative of the anisotropic part of the electron distribution function) does have a small but finite third order effect that is most prominent for plasmas with low average ion charges. This Letter additionally provides a convenient analytic inverse for the isotropic part of the Landau electron–electron collision operator.

The S-Web Origin of Composition Enhancement in the Slow-to-moderate Speed Solar Wind

Connecting the solar wind observed throughout the heliosphere to its origins in the solar corona is one of the central aims of heliophysics. The variability in the magnetic field, bulk plasma, and heavy ion composition properties of the slow wind are thought to result from magnetic reconnection processes in the solar corona. We identify regions of enhanced variability and composition in the solar wind from 2003 April 15 to May 13 (Carrington Rotation 2002), observed by the Wind and Advanced Composition Explorer spacecraft, and demonstrate their relationship to the separatrix–web (hereafter, S-Web) structures describing the corona’s large-scale magnetic topology. There are four pseudostreamer (PS) wind intervals and two helmet streamer (HS) heliospheric current sheet/plasma sheet crossings (and an interplanetary coronal mass ejection), which all exhibit enhanced alpha-to-proton ratios and/or elevated ionic charge states of carbon, oxygen, and iron. We apply the magnetic helicity–partial variance of increments (H m –PVI) procedure to identify coherent magnetic structures and quantify their properties during each interval. The mean duration of these structures are ∼1 hr in both the HS and PS wind. We find a modest enhancement above the power-law fit to the PVI waiting-time distribution in the HS-associated wind at the 1.5–2 hr timescales that is absent from the PS intervals. We discuss our results in the context of previous observations of the ∼90 minutes periodic density structures in the slow solar wind, further development of the dynamic S-Web model, and future Parker Solar Probe and Solar Orbiter joint observational campaigns.

Sputtering produced by vacuum electrospray droplet ions with different sizes and charges

We have been developing a vacuum electrospray droplet ion (V-EDI) beam technique that uses water droplet ions generated by electrospraying aqueous solutions under vacuum. The V-EDI beam is one of the massive cluster ion beams that have the potential to significantly improve the performance of surface analysis. In order to utilize the V-EDI beams effectively as ionization and sputtering probes in secondary ion mass spectrometry and x-ray photoelectron spectroscopy, it is necessary to optimize the sizes and charge states of the droplet ions included in the V-EDI beams. However, the droplet ions themselves in the V-EDI beams are not well understood. In this study, the V-EDI beams generated from the capillaries with different inner diameters were irradiated on polystyrene film samples under constant electrospray and accelerating voltage conditions, and then their surfaces were analyzed with atomic force microscopy and spectroscopic ellipsometer. The impact trace distributions produced by the droplet ions and the sputtered volumes produced by each droplet ion impact were investigated.

Large Individual Ion FTICR Measurements from the Mid-1990s Using Reactions for Charge Determination Mass Spectrometry.

This article discusses from a personal and present-day perspective the first studies of large highly charged individual molecular ions that were conducted using electrospray ionization with Fourier transform ion cyclotron resonance MS in the mid-1990s. These studies are distinguished from Current Charge Detection Mass Spectrometry (CDMS) primarily by their use of individual ion charge state changes due to reactions for accurate charge determination. This work describes the key differences in technologies and methods with present CDMS and the likely implications of these differences. I comment on surprising individual ion behavior observed in some measurements involving increases in charge state, as well as their possible basis, and also briefly discuss the potential utility of the reaction-based mass measurement approach used in the context of what might more globally be referred to as "Charge Determination Mass Spectrometry".

X-ray induced electron and ion fragmentation dynamics in IBr.

Characterization of the inner-shell decay processes in molecules containing heavy elements is key to understanding x-ray damage of molecules and materials and for medical applications with Auger-electron-emitting radionuclides. The 1s hole states of heavy atoms can be produced by absorption of tunable x rays and the resulting vacancy decays characterized by recording emitted photons, electrons, and ions. The 1s hole states in heavy elements have large x-ray fluorescence yields that transfer the hole to intermediate electron shells that then decay by sequential Auger-electron transitions that increase the ion's charge state until the final state is reached. In molecules, the charge is spread across the atomic sites, resulting in dissociation to energetic atomic ions. We have used x-ray/ion coincidence spectroscopy to measure charge states and energies of Iq+ and Brq'+ atomic ions following 1s ionization at the I and Br K-edges of IBr. We present the charge states and kinetic energies of the two correlated fragment ions associated with core-excited states produced during the various steps of the cascades. To understand the dynamics leading to the ion data, we develop a computational model that combines Monte-Carlo/Molecular-Dynamics (MC/MD) simulations with a classical over-the-barrier model to track inner-shell cascades and redistribution of electrons in valence orbitals and nuclear motion of fragments.

Study of Mn ion charge state in Zn2TiO4 and its impact on the photoluminescence and optical absorption spectra

Study of Mn ion charge state in Zn2TiO4 and its impact on the photoluminescence and optical absorption spectra

Experiment and simulation of generation of highly charged ions in a pulsed vacuum arc

A comparison is made of experimental results on the generation of multiply-charged bismuth ions in a vacuum arc plasma with a current pulse of half maximum width 2.5 μs and maximum amplitude 3 kA, and numerical simulation of the generation of multiply-charged bismuth ions in this plasma. Images of the luminous arc plasma were obtained experimentally with nanosecond exposure times at different times throughout the arc current pulse, and simultaneously the ion mass-to-charge composition of the plasma was measured at these times. It is shown that the generation of bismuth ions with charge states of 10+ and higher is associated with compression of the plasma column by its own azimuthal magnetic field, which occurs when the arc pulse current reaches its maximum value. Based on a hybrid hydrodynamic model, the spatial distributions of the arc plasma density, electron temperature, and charge state composition of plasma ions were calculated, which makes it possible to obtain a calculated image of the plasma glow. A comparison of the experimental ion charge-state distributions and photographs of the plasma glow with data obtained from the calculation shows good agreement, which theoretically confirms the generation of high charge state ions during pinching of the arc column.

Separation and Simultaneous Trapping of Multiply Charged and Singly Charged Ions for Mass Spectrometry: Application to Lipid Mixtures.

Conventional electrospray ionization (ESI) of mixtures can give rise to singly and multiply charged analyte species that overlap in mass-to-charge (m/z) ratios, which can complicate the analysis of individual components. The overlap in m/z for ions of different mass and charge is particularly problematic when ions of low relative abundance are of interest. For example, cardiolipins (CLs) are structurally complex phospholipids present in low relative abundance in the lipidome but play crucial roles in mitochondrial metabolism and various regulatory processes. ESI of CLs in negative ion mode shows abundant doubly deprotonated ions and minor singly deprotonated ions. In the ESI of lipid extracts, highly abundant singly charged phospholipids extensively overlap in m/z space with CL dianions of much lesser abundance, thereby complicating the study of the CLs. To address this challenge, we employed a gas-phase approach to separate singly charged ions from a population of ions of mixed charge states while allowing for the storage of one or both of the separated ion populations. Herein, we describe the considerations for applying enhanced singly charged (ESC) and enhanced multiply charged (EMC) scans to perform a gas-phase separation of singly charged lipids from doubly charged lipids in an Escherichia coli extract. This method allows for improved signal-to-noise (S/N) ratio of low abundance ions with minimal overall signal loss, removal of "chemical noise" arising from singly charged ions, and allows for retention of spatially separated ions within a mass spectrometer.

Effect of solution acidity on cytochrome c conformations of alternating current electrospray ionization mass spectrometry

AbstractThis paper reports notable observations regarding the ion charge states of thermally stable cytochrome c, generated using an alternating current (AC) electrospray ionization (ESI) device. An AC ESI sprayer entrains low‐mobility ions to accumulate at the meniscus cone tip prior to the ejection of detached aerosols to produce analyte ions. Therefore, as the solvent acidity varies, protein ions entrained in the AC cone tip are found to change conformation less significantly compared with those in the direct current (DC) cone. We acquired the AC ESI mass spectra of cytochrome c at pH range from 2 to 4. Unlike the DC ESI mass spectra showing clear conformation changes due to denaturing, the AC spectra indicated that only partial denaturing occurs even at extremely acidic pH 2. More native cytochrome c in lower charge states therefore remained. Moreover, with a solvent mixture of aqueous buffer and acetonitrile (70:30), partially denatured cytochrome c was still preserved at pH 2 by using AC ESI. Completely denatured proteins are observed at pH 2 by using DC ESI.

Mass Spectrometric study of graphene-oxide irradiated in vacuum by Nd:YAG laser

During the laser ablation of a graphene oxide target in the vacuum with a 1064 nm ns laser at about 60 J/cm2 fluence, the ablation dynamics and molecular emission have been investigated using a quadrupole mass spectrometer (QMS), time-of-flight measures of the emitted ions and dedicated spectroscopies. The plasma characterization has been obtained giving providing the involved ion species and charge states, and the average temperature and density. Increasing the laser fluence the ablation yield, the plasma density and temperature, the velocity of the emitted particles and the emitted mass yields increase. Due to the laser heating a graphene oxide reduction is also observed. The oxygen is emitted as elemental and as part of different functional groups. A strong dehydration and dehydrogenation occur due to the laser pulse energy deposition, testifying the high content of water and hydrogen possessed by graphene oxide.

Comparison of the Composition of ICMEs from Active Regions and Quiet-Sun Regions

The composition of interplanetary coronal mass ejections (ICMEs), including the ionic charge states and elemental abundances of heavy elements, is tightly correlated with their source regions and eruption processes. This can help in analyzing the eruption mechanisms and plasma origins of CMEs, and deepen our understanding of energetic solar activities. The active regions and quiet-Sun regions have different physical properties; thus, from a statistical point of view, ICMEs originating from the two types of regions should exhibit different compositional characteristics. To demonstrate the differences comprehensively, we conduct survey studies on the ionic charge states of five elements (Mg, Fe, Si, C, and O) and the relative abundances of six elements (Mg/O, Fe/O, Si/O, C/O, Ne/O, and He/O) within ICMEs from 1998 February to 2011 August using data from the Advanced Composition Explorer. The results show that ICMEs from active regions have higher ionic charge states and relative abundances than those from quiet-Sun regions. For the active-region ICMEs, we further analyze the relations between their composition and flare class, and find a positive relationship between them, i.e., the higher the classes of the associated flares, the larger the means of the ionic charge states and relative abundances (except the C/O) within ICMEs. As more (less) fractions of ICMEs originate from active regions around the solar maximum (minimum), and active-region ICMEs usually are associated with higher-class flares, our studies might answer why the composition of ICMEs measured near 1 au exhibits a solar cycle dependence.

On the Seed Population of Solar Energetic Particles in the Inner Heliosphere

AbstractParticles measured in large gradual solar energetic particle events are believed to be predominantly accelerated at shocks driven by coronal mass ejections (CMEs). Ion charge state and composition analyses suggest that the origin of the seed particle population for the mechanisms of particle acceleration at CME‐driven shocks is not the bulk solar wind thermal material, but rather a suprathermal population present in the solar wind. This suprathermal population could result from remnant material accelerated in prior solar flares and/or preceding CME‐driven shocks. In this work, we examine the distribution of this suprathermal particle population in the inner heliosphere by combining a magnetohydrodynamic simulation of the solar wind and a Monte Carlo simulation of particle acceleration and transport. Assuming that the seed particles are uniformly distributed near the Sun by solar flares of various magnitudes, we study the longitudinal distribution of the seed population at multiple heliocentric distances. We consider a nonuniform background solar wind, consisting of fast and slow streams that lead to compression and rarefaction regions within the solar wind. Our simulations show that the seed population at a particular location (e.g., 1 au) is strongly modulated by the underlying solar wind configuration. Corotating interaction regions and merged interactions regions can strongly alter the energy spectra of the seed particle populations. In addition, cross‐field diffusion plays an important role in mitigating strong variations of the seed population in both space and energy.

Charge Evolution for N2 + Ion Passing Through Ag Target

Charge state is a key factor for the ion stopping and energy deposition. It is helpful to understand the physics mechanics for interaction between ion and target by studying the charge state. In this paper, nitrogen molecular ion charge evolution in Ag target is studied. It is shown that the charge state of the trailing ion is oscillating, while the leading ion doesn’t show the similar behavior due to the wake effects aroused by the electronic exciting of the target electron.

Detailed composition of iron ions in interplanetary coronal mass ejections based on a multipopulation approach

Context. Coronal mass ejections (CMEs) are extremely dynamical, large-scale events in which plasma – but not only the coronal plasma – is ejected into interplanetary space. If a CME is detected in situ by a spacecraft located in the interplanetary medium, it is then called an interplanetary coronal mass ejection (ICME). This solar activity has been studied widely since coronagraphs were first flown into space in the early 1970s. Aims. Charge states of heavy ions reflect important information about the coronal temperature profile due to the freeze-in effect and it is estimated that iron ions freeze in at heights of ∼5 solar radii. However, the measured charge-state distribution of iron ions cannot be composed of only one single group of plasma. To identify the different populations of iron charge-state composition of ICMEs and determine their sources, we developed a model that independently uses two, three, and four populations of iron ions to fit the measured charge-state distribution in ICMEs detected by the Advanced Composition Explorer (ACE) at 1 AU. Methods. Three parameters are used to identify a certain population, namely freeze-in temperature, relative abundance, and kappa value (κ), which together describe the potential non-Maxwellian kappa distributions of coronal electrons. Our method chooses the reduced chi-squared to describe the goodness of fit of the model to the observations. The parameters of our model are optimized with the covariance-matrix-adaptation evolution strategy (CMA-ES). Results. Two major types of ICMEs are identified according to the existence of hot material, and both, that is, the cool type and the hot type, have two main subtypes. Different populations in those types have their own features related to freeze-in temperature and κ. The electron velocity distribution function usually contains a significant hot tail in typical coronal material and hot material, while the Maxwellian distribution appears more frequently in mid-temperature material. Our model is also suitable for all types of solar wind and the existence of hot populations as well as the change of temperatures of individual populations may indicate boundaries between ICMEs and individual solar wind streams.

Evidence of production of keV Sn+ ions in the H2 buffer gas surrounding an Sn-plasma EUV source

Charge-state-resolved kinetic energy spectra of Sn ions ejected from a laser-produced plasma (LPP) of Sn have been measured at different densities of the H2 buffer gas surrounding a micro-droplet LPP. In the absence of H2, energetic keV Sn ions with charge states ranging from 4+ to 8+ are measured. For the H2 densities used in the experiments no appreciable stopping or energy loss of the ions is observed. However, electron capture by Sn ions from H2 results in a rapid shift toward lower charge states. At the highest H2 pressure of mbar, only Sn2+ and Sn+ ions are measured. The occurrence of Sn+ ions is remarkable due to the endothermic nature of electron capture by Sn2+ ions from H2. To explain the production of keV Sn+ ions, it is proposed that their generation is due to electron capture by metastable Sn ions. The gateway role of metastable Sn is underpinned by model simulations using atomic collision cross sections to track the charge states of Sn ions while traversing the H2 buffer gas.

A multiparameter optimization in middle-down analysis of monoclonal antibodies by LC-MS/MS.

In antibody-based drug research, a complete characterization of antibody proteoforms covering both the amino acid sequence and all posttranslational modifications remains a major concern. The usual mass spectrometry-based approach to achieve this goal is bottom-up proteomics, which relies on the digestion of antibodies but does not allow the diversity of proteoforms to be assessed. Middle-down and top-down approaches have recently emerged as attractive alternatives but are not yet mastered and thus used in routine by many analytical chemistry laboratories. The work described here aims at providing guidelines to achieve the best sequence coverage for the fragmentation of intact light and heavy chains generated from a simple reduction of intact antibodies using Orbitrap mass spectrometry. Three parameters were found crucial to this aim: the use of an electron-based activation technique, the multiplex selection of precursor ions of different charge states, and the combination of replicates.

Bombardment of CO Ice by Cosmic Rays. I. Experimental Insights into the Microphysics of Molecule Destruction and Sputtering

We present a dedicated experimental study of microscopic mechanisms controlling radiolysis and sputtering of astrophysical ices upon bombardment by cosmic-ray ions. Such ions are slowed down owing to inelastic collisions with bound electrons, resulting in ionization and excitation of ice molecules. In experiments on CO ice irradiation, we show that the relative contribution of these two mechanisms of energy loss to molecule destruction and sputtering can be probed by selecting ion energies near the peak of the electronic stopping power. We have observed a significant asymmetry, in both the destruction cross section and the sputtering yield, for pairs of ion energies corresponding to the same values of the stopping power on either side of the peak. This implies that the stopping power does not solely control these processes, as usually assumed in the literature. Our results suggest that electronic excitations represent a significantly more efficient channel for radiolysis and, likely, for sputtering of CO ice. We also show that the charge state of incident ions and the rate for CO+ production in the ice have a negligible effect on these processes.

Energy deposition and formation of nanostructures in the interaction of highly charged xenon ions with gold nanolayers

The effect of the deposition of kinetic energy and neutralization energy of slow highly charged xenon ions on the process of the nanostructures creation at the surface of gold nanolayers is investigated. The nanolayers of thickness of 100 nm were prepared by e-beam evaporation of gold on crystalline silicon Si(100) substrate. The samples were irradiated at the Kielce EBIS facility of the Jan Kochanowski University (Kielce, Poland), under high vacuum conditions. The irradiations were performed for constant kinetic energy 280 keV and different ions charge states (Xeq+, q = 25, 30, 35, 36 and 40) and for constant charge state Xe35+ and different kinetic energies: 280 keV, 360 keV, 420 keV and 480 keV. The fluence of the ions was on the level of 1010 ions/cm2. Before and after irradiation the nanolayer surfaces were investigated using the atomic force microscope.As the result, well pronounced modifications of the nanolayer surfaces in the form of craters have been observed. A systematic analysis of the crater sizes (diameter on the surface and depth) allowed us to determine the influence of the deposited kinetic and the neutralization energy on the size of the obtained nanostructures. The results are theoretically interpreted within the micro-staircase model based on the quantum two-state vector model of the ionic Rydberg states population. The charge dependent ion–atom interaction potential inside the solid is used for the calculation of the nuclear stopping power. According to the model the formation of the nanostructures is governed by the processes of the ionic neutralization in front of the surface and the kinetic energy loss inside the solid. The interplay of these two types of processes in the surface structure creation is described by the critical velocity. Using the proposed theoretical model, the neutralization energy, deposited kinetic energy and critical velocities were calculated and compared qualitatively with the experimental results. The results are consistent (after normalization) with previous experimental data and molecular dynamics simulations for single ionized Xe and crystalline gold surface.

Analysis of Ti nanolayers irradiated with Xeq＋ ions using synchrotron radiation based X-ray reflectometry

To characterize morphology and physicochemical properties of nanolayers the surface-sensitive X-ray spectroscopy techniques are often successfully applied. These techniques are still being developed in order to achieve better depth resolution and detection limits. In this article, we present measurements of morphology of Ti nanolayers (deposited on Si substrate) with thickness of 25 nm, 50 nm and 75 nm, unmodified and irradiated with Xeq＋ ions (where q is the charge state of the ion), which were carried out using synchrotron radiation (SR) based XRR technique. The nanolayers were irradiated with low-energy (of the order of hundreds of keV) highly charged Xeq＋ (q = 25, 30, 35) ions, at the Kielce EBIS facility (Jan Kochanowski University, Kielce, Poland). The SR-XRR measurements were performed at Elettra Synchrotron X-ray fluorescence beamline, using X-ray beam with energy of 6.0 keV. The obtained reflectivity curves were modelled by creating a structure consisting (from the bottom to the top) of silicon substrate (Si), main Ti layer, TiO2 layer, and TiO2(a) amorphous layer, with contamination of hydrocarbons, carboxylates or alkoxides. The experimental results obtained with the SR-XRR technique for the nanolayers, unmodified and irradiated with the Xeq＋, show the dependence of the TiO2 layers morphology on the Xe ions charge state. In the article the sample preparation, measurement using SR-XRR and the data analysis procedures are described in details and the advantages and disadvantages of the SR-XRR technique in the context of nanolayer studies are discussed.

The constraint of plasma power balance on runaway avoidance

In a post-thermal-quench plasma, mitigated or unmitigated, the plasma power balance is mostly between collisional or Ohmic heating and plasma radiative cooling. In a plasma of atomic mixture with α labeling the atomic species, the power balance sets the plasma temperature, ion charge state distribution with i the charge number, and through the electron temperature and ion charge state distribution the parallel electric field Since the threshold electric field for runaway avalanche growth is also set by the atomic mixture, ion charge state distribution and its derived quantity, the electron density the plasma power balance between Ohmic heating and radiative cooling imposes a stringent constraint on the plasma regime for avoiding and minimizing runaways when a fusion-grade tokamak plasma is rapidly terminated.