Ion-neutral Collisions Research Articles

Energy Transport and Heating by Torsional Alfvén Waves Propagating from the Photosphere to the Corona in the Quiet Sun

Abstract In the solar atmosphere, Alfvén waves are believed to play an important role in the transfer of energy from the photosphere to the corona and solar wind, and in the heating of the chromosphere. We perform numerical computations to investigate the energy transport and dissipation associated with torsional Alfvén waves propagating in magnetic flux tubes that expand from the photosphere to the corona in quiet-Sun conditions. We place a broadband driver at the photosphere that injects a wave energy flux of 107 erg cm−2 s−1 and consider Ohm’s magnetic diffusion and ion–neutral collisions as dissipation mechanisms. We find that only a small fraction of the driven flux, ∼105 erg cm−2 s−1, is able to reach coronal heights, but it may be sufficient to partly compensate the total coronal energy loss. The frequency of maximal transmittance is ∼5 mHz for a photospheric field strength of 1 kG and is shifted to smaller/larger frequencies for weaker/stronger fields. Lower frequencies are reflected at the transition region, while higher frequencies are dissipated, producing enough heat to balance chromospheric radiative losses. Heating in the low and middle chromosphere is due to Ohmic dissipation, while ion–neutral friction dominates in the high chromosphere. Ohmic diffusion is enhanced by phase mixing because of the expansion of the magnetic field. This effect has the important consequence of increasing the chromospheric dissipation and, therefore, reducing the energy flux that reaches the corona. We provide empirical fits of the transmission coefficient that could be used as input for coronal models.

Composition and charge state influence on the ion-neutral collision cross sections of protonated N-linked glycopeptides: an experimental and theoretical deconstruction of coulombic repulsion vs. charge solvation effects.

Ion mobility spectrometry (IMS) is of significant interest as a platform for glycoanalysis. While much attention has been focused on the resolution of isomeric carbohydrates and glycoconjugates, another appealing aspect of IMS is the ability to sort different classes of biomolecules into distinct regions of mass vs. mobility space. This capability has potential to greatly simplify glycoproteomic analyses, as glycosylated and non-glycosylated peptides can be rapidly partitioned in the gas phase. Nevertheless, the physical and chemical characteristics of glycopeptides that dictate their mass vs. mobility loci have yet to be systematically investigated. This report presents an IMS study of model protonated glycopeptide ions with systematically varied oligosaccharide topologies, polypeptide sequences, and charge states. In all, over 110 ion-neutral collision cross sections (CCSs) were measured and analyzed in the context of the physicochemical characteristics of the analytes. Glycan size and composition emerged as a decisive factor in dictating the CCS space occupied by the glycopeptides and exerted this influence in a charge state dependent fashion. Furthermore, elongation of the glycan group was found to either increase or decrease glycopeptide CCSs depending on the ion charge state and the size of the glycan. Molecular dynamics (MD) simulations of the gas phase structures and CCSs of selected glycopeptides revealed that the experimental observations were consistent with a glycan size and charge state dependent interplay between destabilizing coulombic repulsion effects (tending to result in more extended structures) and stabilizing charge solvation effects in which the glycan plays a major role (tending to result in more compact structures). Taken together, these IMS and MD findings suggest the possibility of predicting and delineating glycopeptide-enriched regions of mass vs. mobility space for applications in glycoproteomics.

Application of Group I Metal Adduction to the Separation of Steroids by Traveling Wave Ion Mobility Spectrometry.

Steroids represent an interesting class of small biomolecules due to their use as biomarkers and their status as scheduled drugs. Although the analysis of steroids is complicated by the potential for many isomers, ion mobility spectrometry (IMS) has previously shown promise for the rapid separation of steroid isomers. This work is aimed at the further development of IMS separation for the analysis of steroids. Here, traveling wave ion mobility spectrometry (TWIMS) was applied to the study of group I metal adducted steroids and their corresponding multimers for five sets of isomers. Each set of isomers had a minimum of one dimeric metal ion adduct that exhibited a resolution greater than one (i.e., approaching baseline resolution). Additionally, ion-neutral collision cross sections (CCSs) were measured using polyalanine as a calibrant, which may provide an additional metric contributing to analyte identification. Where possible, measured CCSs were compared to previously reported values. When measuring CCSs of steroid isomers using polyalanine as the calibrant, nitrogen CCS values were within 1.0% error for monomeric sodiated adducts and slightly higher for the dimeric sodiated adducts. Overall, TWIMS was found to successfully separate steroids as dimeric adducts of group I metals. Graphical Abstract ᅟ.

Buoyancy-driven Magnetohydrodynamic Waves in a Partially Ionized Plasma

Abstract A magnetohydrodynamic (MHD) fluid description is typically employed to study the magnetized plasma comprising the solar atmosphere. This approach has had many successes in modeling and explaining solar phenomena. Most often, the plasma is assumed to be fully ionized. While this approach is justified in the higher atmosphere, i.e., the solar corona; the temperature in the lower solar atmosphere is such that a large proportion of the fluid may be electrically neutral. This begs the question: to what degree are the results derived from a fully ionized MHD description valid? In this article, we investigate the effect of partial ionization on buoyancy-driven MHD waves (the MHD analog of internal gravity waves) by applying a simplified two-fluid description. We show that previously derived results may be applied, when the fluid is weakly ionized, if the ion–neutral collision frequency is high. We derive dispersion relations for buoyancy-driven MHD waves, which include correction factors and damping rates due to ion–neutral collisions.

Simulations of the Ion Current to a Probe in Plasma with Allowance for Ionization and Ion–Neutral Collisions: II. Cylindrical Probe

Simulations of the Ion Current to a Probe in Plasma with Allowance for Ionization and Ion–Neutral Collisions: II. Cylindrical Probe

Modification of plasma flows in edge and SOL regions by influence of neutral gas

Plasma flows and their profiles in edge and scrape-off layer (SOL) regions of a tokamak plasma are important as these can modify the interchange plasma turbulence. These flows have been investigated in the presence of neutral gas numerically using the two-dimensional model equations. A reduction of poloidal flows, radial particle, and energy fluxes has been observed in the edge and SOL regions by the presence of the neutral gas. The reduction of radial flux is due to the reduction in the radial velocity of the plasma blob. We have investigated Reynolds stress in the presence of the gas. It is found that in the presence of ion-neutral collisions, the magnitude of the stress decreases. The gas also reduces the diamagnetic drift frequency in the edge and SOL regions.

Fourier Transform-Ion Mobility-Orbitrap Mass Spectrometer: A Next-Generation Instrument for Native Mass Spectrometry.

A new instrument configuration for native ion mobility-mass spectrometry (IM-MS) is described. Macromolecule ions are generated by using a static ESI source coupled to an RF ion funnel, and these ions are then mobility and mass analyzed using a periodic focusing drift tube IM analyzer and an Orbitrap mass spectrometer. The instrument design retains the capabilities for first-principles determination of rotationally averaged ion-neutral collision cross sections and high-resolution measurements in both mobility and mass analysis modes for intact protein complexes. Operation in the IM mode utilizes FT-IMS modes (originally described by Knorr ( Knorr , F. J. Anal. Chem . 1985 , 57 ( 2 ), 402 - 406 )), which provides a means to overcome the inherent duty cycle mismatch for drift tube (DT)-IM and Orbitrap mass analysis. The performance of the native ESI-FT-DT-IM-Orbitrap MS instrument was evaluated using the protein complexes Gln K (MW 44 kDa) and streptavidin (MW 53 kDa) bound to small molecules (ADP and biotin, respectively) and transthyretin (MW 56 kDa) bound to thyroxine and zinc.

Molecular dynamics simulations of wake structures behind a microparticle in a magnetized ion flow. II. Effects of velocity spread and ion collisions

The influence of velocity spread and ion-neutral collisions on the wake of a microparticle in a collisional magnetized ion flow is explored by means of molecular dynamics simulations. The ion flow is described in the constant-mean-free-path limit. A constant electric field is superimposed that maintains the ion drift at the Bohm speed and approximates conditions in the plasma sheath. The contribution of ion Landau damping to the wake structure is separated by simulations with a collisionless drift distribution. It is found that ion Landau damping and collisions have a counteracting effect on the ion density in the focus region. The dynamic shadows that are a typical feature of collisionless magnetized wakes with cold ion beams are damped by the velocity spread and vanish by a collision-enhanced ion density in the wake. Dynamic shadows reappear only at very high magnetic fields, B ≈ 10 T. In two-particle arrangements, the full collisional model shows that horizontal attractive forces persist up to B = 4 T but become repulsive for higher magnetization.

A solvable model for the basic properties of a simple magnetized plasma torus

A simple magnetized plasma torus is modeled by using a ‘top-hat’ density variation. The benefit of this simplification is an exactly solvable model, allowing for a few additions, such as an externally maintained parabolic steady state potential variation imposed on the plasma. The combined effects of the resulting plasma rotation and the plasma polarization due to magnetic field gradient particle drifts can be described. The stabilizing and confining effects of plasma rotation are explicitly demonstrated. In a special high plasma density limit the results are confirmed by a more general model, indicating that the results of the top-hat model can be used with confidence in more general cases. A small vertical magnetic field component can be included for a plasma with neutral collisions and its influence on the electron dynamics studied. The effects of ion–neutral collisions are also included. The rotation and polarization of the plasma has different effects on the time variations of the plasma density and potential. As a reference we use data from the Blaamann device at the University of Tromsø obtained by a movable multi-probe, measuring variations in density, floating potential and an electric field component. The fluctuations in the plasma are characterized by auto-correlations and by cross-correlations between the signal from a fixed reference probe and data. The model accounts adequately for the phase variations of the signals for varying spatial multi-probe positions.

Simulation study on the vapour shielding at solid walls under transient heat loads using weighted particle model

Vapour shielding at solid walls is expected for a future fusion reactor in case of large heat load due to transient events. In order to estimate the dissipation of the incoming heat flux by the vapour shielding, a simulation code called PIXY, using a weighted particle model, is developed. First, a validation study is undertaken. Vapour shielding of an aluminium‐coated tungsten specimen was experimentally observed in a plasma gun device. Results are reproduced by the PIXY simulation. Then, the code is applied to the transient edge‐localized mode (ELM) heat flux for the reactor condition. It was found that the ion–neutral collision, as well as radiative cooling, is a dominant phenomenon for the heat flux dissipation in both cases. As the maximum heat flux increases, oscillating phenomena appear remarkably, which have been observed in other experimental studies on vapour shielding.

Evolution of ion–ion acoustic instability in multi-ion plasma sheaths

The generation of ion-acoustic solitary waves is investigated in a nonuniform multicomponent collisional plasma sheath containing cold ions and Boltzmann electrons to probe the formation and physics of modulation of nonlinear ion-acoustic waves. The new model for the plasma is adapted to include the effects of ion production-loss and momentum loss terms due to ion-neutral collisions, and implementation related to space and laboratory plasma applications are discussed. The discrete modes, the instability conditions and the growth rate of the streaming instability with the effect of the present plasma parameters are calculated based on the approximate but yet precise complex dispersion relation. The marginal stability curve, characterized by mode bifurcation, cutoff, and complex fold point, indicates a growth rate of a few percents of effective plasma frequency. The damping of ion-acoustic is affected by heavy neutrals, and its maximum rate found near the ion-neutral collision frequency. The variable-coefficient Korteweg-de Vries equation is derived via reductive perturbation method to govern the dynamics of small- as well as large-amplitude solitons. It is found that the propagating nonlinear coherent structures through the created ion phase-space vortices lead to ion trapping and acceleration, and the modulation of ion-acoustic instabilities in the turbulent region. The effect of ion streaming motion on the driven solitons and modulation instability for the variable-coefficient Korteweg-de Vries equation is numerically investigated in detail. The theoretical results can be applied to the observation of electrostatic waves in space plasmas, in industrial pair-ion plasmas as well as in laboratory dusty plasmas.

Ion-Flow-Induced Excitation of Electrostatic Cyclotron Mode in Magnetized Dusty Plasma

The stability of electrostatic cyclotron mode is investigated in a flowing magnetized dusty plasma in the presence of strong ion–neutral collisions. In the high magnetic field limit, when the dust magnetization becomes important, it is expected that the collective behavior of magnetized dust grains suspended in the near-sheath region substantially influences the dispersion properties of electrostatic modes. The growth/damping of the collective excitation is significantly controlled by such parameters as the ion–neutral collision frequency, Mach number, and magnetic field strength. In our case, the explicit dependence of the Mach number on the magnetic field and collision frequency has been taken into account and possible implications on the stability of the mode is analyzed. Streaming instability of cyclotron modes may be important to understand issues related to the interaction mechanism between dust grains and other associated phenomena like Coulomb crystallization, phase behavior, transport properties, etc., in the relatively strong magnetic field limit, which is currently accessible in the DPD (Kiel University) and MDPX (PSL, Auburn University) experiments.

Electrostatic wave modulation in collisional pair-ion plasmas

The effects of ion-neutral collision on the electrostatic wave packets in the absence of the magnetic field in a pair-ion plasma have been investigated. Considering a two-fluid plasma model with the help of the standard perturbation technique, two distinct electrostatic modes have been observed, namely, a low-frequency ion acoustic mode and a high-frequency ion plasma mode. The dynamics of the modulated wave is governed by a damped nonlinear Schrödinger equation. Damping of the soliton occurs due to the ion-neutral collision. The analytical and numerical investigation reveals that the ion acoustic mode is both stable and unstable, which propagates in the form of dark solitons and bright solitons, respectively, whereas the ion plasma mode is unstable, propagating in the form of a bright soliton. Results are discussed in the context of the fullerene pair-ion plasma experiments.

The effect of DC voltage polarity on ionic wind in ambient air for cooling purposes

Gas flows can be induced by gas discharges like DC coronas because neutral molecules gain momentum by ion-neutral collisions. This can be used for active cooling and has advantages over mechanical fans. We investigate ionic wind by a DC corona discharge under different conditions with an emphasis on the effects of voltage polarity and the transition between different discharge regimes. We also consider the gas temperature of a DC corona which is important when it is to be used for cooling purposes. Although DC coronas are usually characterized as low temperature plasmas, gas heating can have a significant impact on flow generation, especially at higher operating voltages. In this paper, a 5–20 kV DC voltage of positive and negative polarity is applied to a needle–cylinder electrode. The ionic wind velocity at the exit of the cylinder electrode is measured by hot wire anemometry and the emission spectrum is used to study the gas temperature. It is found that the flow velocity induced by positive coronas is higher than that by negative coronas for voltages above 10–15 kV, which is also demonstrated by a phenomenological EHD force model. Furthermore, a heated column is observed by Schlieren technique for both voltage polarities. An improved self-consistent ionic wind model considering heat transfer is built to study the temperature distribution. The simulation results indicate that the gas flow velocity is lower on the symmetry axis when the temperature gradient is taken into account, something which is usually ignored in ionic wind simulations.

Anomalous transport of charged dust grains in a magnetized collisional plasma: A molecular dynamics study

Anomalous diffusion of charged dust grains immersed in a plasma in the presence of strong ion-neutral collision, flowing ions, and a magnetic field has been observed. Molecular Dynamics simulation confirms the deviation from normal diffusion in an ensemble of dust grains probed in laboratory plasma chambers. Collisional effects are significant in governing the nature of diffusion. In order to have a clear idea on the transport of particles in a real experimental situation, the contribution of streaming ions and the magnetic field along with collision is considered through the relevant interaction potential. The nonlinear evolution of Mean Square Displacement is an indication of the modification in particle trajectories due to several effects as mentioned above. It is found that strong collision and ion flow significantly affect the interparticle interaction potential in the presence of the magnetic field and lead to the appearance of the asymmetric type of Debye Hückel (D H) potential. Due to the combined effect of the magnetic field, ion flow, and collision, dusty plasma exhibits a completely novel behavior. The coupling parameter Γ enhances the asymmetric D H type potential arising due to ion flow, and this may drive the system to a disordered state.

Collision cross section (CCS) measurement by ion cyclotron resonance mass spectrometry with short-time Fourier transform.

The collision cross section (CCS) is an important shape parameter which is often used in molecular structure investigation. In Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), the CCS affects the ion signal damping shape due to the effect of ion-neutral collisions. It is potential to obtain ion CCS values from FTICR-MS with the help of a proper ion-collision model. We have developed a rapid method to obtain the ion damping profile and CCS for mixtures by only one FTICR-MS measurement. The method utilizes short-time Fourier transform (STFT) to process FTICR-MS time domain signals. The STFT-processed result is a three-dimensional (3D) spectrum which has an additional time axis in addition to the conventional mass-to-charge ratio and intensity domains. The damping profile of each ion can be recognized from the 3D spectrum. After extracting the decay profile of a specified ion, all the three ion-neutral collision models were tested in curve fitting. The hard-sphere model was proven to be suitable for our experimental setup. A linear relationship was observed between the CCS value and hard-sphere model parameters. Therefore, the CCS values of all the peaks were obtained through the addition of internal model compounds and linear calibration. The proposed method was successfully applied to determine the CCSs of fatty acids and polyalanines in a petroleum gas oil matrix. This technique can be used for simultaneous measurement of cross sections for many ions in congested spectra.

Determination of Collision Cross-Sections of Protein Ions in an Orbitrap Mass Analyzer.

We demonstrate a method for determining the collision cross-sections (CCSs) of protein ions based on the decay rate of the time-domain transient signal from an Orbitrap mass analyzer. Multiply charged ions of ubiquitin, cytochrome c, and myoglobin were generated by electrospray ionization of both denaturing solutions and ones with high salt content to preserve native-like structures. A linear relationship between the pressure in the Orbitrap analyzer and the transient decay rate was established and used to demonstrate that the signal decay is primarily due to ion-neutral collisions for protein ions across the entire working pressure range of the instrument. The CCSs measured in this study were compared with previously published CCS values measured by ion mobility mass spectrometry (IMS), and results from the two methods were found to differ by less than 7% for all charge states known to adopt single gas-phase conformations.

Existence regimes for shocks in inhomogeneous magneto-plasmas having entropy

The finding of connection of plasma density and temperature with entropy gives an incitement to study different plasma models with respect to entropy. Nonlinear dissipative one- and two-dimensional structures (shocks) are investigated in nonuniform magnetized plasma with respect to entropy. The dissipation comes in the medium through ion-neutral collisions. The linear dispersion relation is derived. The Korteweg–deVries-Burgers and Kadomtsev-Petviashvili-Burgers equations are derived for nonlinear drift waves in 1-D and 2-D by employing the drift approximation. It is found that vd/u (vd is the diamagnetic drift velocity and u is the velocity of nonlinear structure) plays a significant role in the shock formation. It is also found that entropy has a significant effect on the strength of shocks. It is noticed that vd/u determines the rarefactive and compressive nature of the shocks. It is observed that upper and lower bounds exist for the shock velocity. It is also observed that the existing regimes for both one- and two-dimensional shocks for kappa distributed electrons are different from shocks with Cairns distributed electrons. Both rarefactive and compressive shocks are found for the 1-D drift waves with kappa distributed electrons. Interestingly, it is noticed that entropy enhances the strength of one- and two-dimensional shocks.

Ion acoustic solitons in magnetized collisional non-thermal dusty plasmas

The oblique propagation of ion-acoustic solitary waves (IASWs) is considered, in a magnetized non-thermal collisional dusty plasma, composed of non-Maxwelian κ-distributed electrons, inertial ions, and stationary dust. The reductive perturbation approach is adopted to derive the damped Korteweg de-Vries (dKdV) equation, and the dissipative oblique ion-acoustic wave properties are investigated in terms of different key plasma parameters via the numerical solution of the dKdV equation. The collisional effect, describing the ion-neutral collision in the plasma, is taken into account, and seen to influence the dynamics of IASWs significantly. The basic features of IASWs are observed to modify, and the polarity of the wave is seen to change due to the variation of dust to that of ion number density and also due to the variation of the supethermality index κ in the considered plasma system.

Behavior of collisional sheath in electronegative plasma with q-nonextensive electron distribution

Electronegative plasma sheath is addressed in a collisional unmagnetized plasma consisting of q-nonextensive electrons, Boltzmann distributed negative ions and cold fluid positive ions. Considering the positive ion-neutral collisions and ignoring the effects of ionization and collisions between negative species and positive ions (neutrals), a modified Bohm sheath criterion and hence floating potential are derived by using multifluid model. Using the modified Bohm sheath criterion, the sheath characteristics such as spatial profiles of density, potential and net space charge density have been numerically investigated. It is found that increasing values of q-nonextensivity, electronegativity and collisionality lead to a decrease of the sheath thickness and an increase of the sheath potential and the net space charge density. With increasing values of the electron temperature to negative ion temperature ratio, the sheath thickness increases and the sheath potential as well as the net space charge density in the sheath region decreases.