Resonant Charge Exchange Research Articles

Broad beam source of fast atoms produced as a result of charge exchange collisions of ions accelerated between two plasmas

Experimental study of a fast argon atom beam source is carried out and the study results are presented. The source comprises a 90-mm deep and 210-mm in diameter hollow cathode as well as a flat emission grid, both electrodes made of titanium. The study revealed main factors, which influence the zone diameter of homogeneous substrate etching by a broad beam of fast argon atoms, produced as a result of charge exchange collisions of ions, accelerated between a plasma emitter inside the hollow cathode and a secondary plasma in the working vacuum chamber, the plasmas being separated from each other with the grid. It is shown that at a distance from the grid, exceeding the resonant charge exchange length up to 4 times, elastic collisions have no appreciable impact on the spatial distribution of the etching rate in the vacuum chamber. The homogeneous etching zone diameter is mainly influenced by angular characteristics of accelerated particles in the grid plane. At a constant beam power up to 3–5 kW the diameter is rising with a decrease of their energy and with a corresponding increase of the beam current.

High temperature Mars atmosphere. Part I: transport cross sections

In the perspective of higher approximations of the Chapman-Enskog theory for transport property calculations, existing transport cross sections databases for interactions involving Earth atmosphere species have been updated and extended to Mars atmosphere components, proposing a phenomenological approach for the derivation of the relevant elastic collision integrals in neutral-neutral and neutral-ion interactions. Inelastic collision integrals terms, due to resonant charge exchange channels, have been considered and the asymptotic approach extended to the estimation of charge transfer cross section of multiple resonant processes.

Possible physical properties of the flow in the vicinity of the heliopause

An interface between the fully ionized hydrogen plasma of the solar wind (SW) and the partially ionized hydrogen gas flow of the local interstellar medium (LISM) is formed as a region where there is a strong interaction between these two flows. The interface is bounded by the solar wind termination shock (TS) and the LISM bow shock (BS) and is separated on two regions by the heliopause (HP) separating the solar wind and charged component of the LISM (plasma component below). The BS is formed due to the deceleration of the supersonic LISM flow relative to the solar system. Regions of the interface between the TS and HP and between the HP and BS were in literature named as the inner and outer heliosheaths, respectively. An investigation of the structure and physical properties of the heliosheath is at present especially interested due to the fact that Voyager-1 and Voyager-2 have crossed the TS in December 2004 (Burlaga, L.F., Ness, N.F., Acuna, M.Y., et al. Crossing the termination shock into the the heliosheath. Magnetic fields. Science 309, 2027–2029, 2005; Fisk, L.A. Journey into the unknown beyond. Science 309, 2016–2017, 2005; Decker, R.B., Krimigis, S.M., Roelof, E.C., et al. Voyager 1 in the foreshock, termination shock and heliosheath. Science 309, 2020–2024, 2005; Stone, E.C., Cummings, A.C., McDonald, F.B., et al. Voyager 1 explores the termination shock region and the heliosheath beyond. Science 309, 2017–2020, 2005) and in September 2007 (Jokipii, J.R. A shock for Voyager 2. Nature 454, 38–39, 2008; Gurnett, D.A., Kurth, W.S. Intense plasma waves at and near the solar wind termination shock. Nature 454, 78–80, 2008. doi: 10.1038/nature07023; Wang, L., Lin, R.P., Larson, D.E., Luhmann, J.G. Domination of heliosheath pressure by shock-accelerated pickup ions from observations of neutral atoms. Nature 454, 81–83, 2008. doi: 10.1038/nature07068.14; Burlaga, L.F., Ness, N.F., Acuna, M.H., et al. Magnetic fields at the solar wind termination shock. Nature 454, 75–77, 2008. doi: 10.1038/nature07029; Richardson, J.D., Kasper, J.C., Wang, C., et al. Cool heliosheath plasma and deceleration of the upstream solar wind at the termination shock. Nature 454, 63–66, 2008. doi: 10.1038/nature07024; Stone, E.C., Cummings, A.C., McDonald, F.B., et al. An asymmetric solar wind termination shock. Nature 454, 71–74, 2008. doi: 10.1038/nature07022; Decker, R.B., Krimigis, S.M., Roelof, E.C., et al. Mediation of the solar wind termination shock by non-thermal ions. Nature 454, 67–70, 2008. doi: 10.1038/nature 07030), respectively, and entered to the inner heliosheath. Gas dynamic and magneto-hydrodynamic (MHD) problems of the heliosheath structure are theoretically discussed in this paper. In particular, the problems of the heliopause instability, effects of the resonance charge exchange processes, magnetic fields are considered. The effect of the LISM magnetic field on the outer heliosheath structure is discussed. It is shown that new theoretical problems must be solved to predict experimental results which can be obtained onboard Voyagers in the nearest time and in future possible projects.

A non-Maxwellian kinetic approach for charging of dust particles in discharge plasmas

Nanoparticle charging in a capacitively coupled radio frequency discharge in argon is studied using a particle in cell Monte Carlo collisions method. The plasma parameters and dust potential were calculated self-consistently for different unmovable dust profiles. A new method for definition of the dust floating potential is proposed, based on the information about electron and ion energy distribution functions, obtained during the kinetic simulations. This approach provides an accurate balance of the electron and ion currents on the dust particle surface and allows us to precisely calculate the dust floating potential. A comparison of the obtained floating potentials with the results of the traditional orbital motion limit (OML) theory shows that in the presence of the ion resonant charge exchange collisions, even when the OML approximation is valid, its results are correct only in the region of a weak electric field, where the ion drift velocity is much smaller than the thermal one. With increasing ion drift velocity, the absolute value of the calculated dust potential becomes significantly smaller than the theory predicts. This is explained by a non-Maxwellian shape of the ion energy distribution function for the case of fast ion drift.

A multispecies chemistry model of Io's local interaction with the Plasma Torus

We model the local interaction between the plasma in the torus and Io's neutral corona (inside ∼6 RIo), focusing on the multispecies chemistry outside the collision‐dominated ionosphere. We include a detailed chemistry of S, O, SO2, SO under ionization, charge exchange, and recombination processes in a parcel of plasma that follows a prescribed flow field around Io's ionosphere and interacts with the neutral density profiles in the corona, as constrained by available observations. We compare the model results to the Galileo plasma observations in Io's wake (GLL/J0). We conclude the following: (1) The plasma characteristics along GLL/J0 require a dense SO2 corona confined close to Io (<2 RIo). (2) Molecular SO2 chemistry dominates the interaction, with atomic chemistry playing a negligible role. (3) SO2+ is the main output ion of the local interaction, but it recombines and dissociates rapidly so that the contribution of the local interaction to the global mass and energy supply of the torus is very small. (4) The high density of plasma observed in the wake requires a supplemental ionization source beyond the thermal electrons of the torus, and we estimate the ionization due to the (∼350 eV) field‐aligned electron beams observed around Io. (5) Assuming a SO2 atmosphere/corona with a vertical column of 6 × 1016 cm−2 and a prescribed deceleration of the flow around Io, we estimate a local ion mass production rate of ∼200 kg/s. We also compute a neutral loss rate of ∼2400 kg/s and a pick‐up current of ∼5.2 MAmp, both dominated by the SO2 resonant charge exchange reaction.

Kinetic-Hydrodynamic Models of the Solar Wind Interaction with the Partially Ionized Supersonic Flow of the Local Interstellar Gas: Predictions and Interpretations of the Experimental Data

At present there is no doubt that the local interstellar medium (LISM) is mainly partially ionized hydrogen gas moving with a supersonic flow relative to the solar system. The bulk velocity of this flow is approximately equal ∼26 km/s. Although the interaction of the solar wind with the charged component (below plasma component) of the LISM can be described in the framework of hydrodynamic approach, the interaction of H atoms with the plasma component can be correctly described only in the framework of kinetic theory because the mean free path of H atoms in the main process of the resonance charge exchange is comparable with a characteristic length of the problem considered. Results of self-consistent, kinetic-hydrodynamic models are considered in this review paper. First, such the model was constructed by Baranov and Malama (J. Geophys. Res. 98(A9):15,157–15,163, 1993). Up to now it is mainly developed by Moscow group taking into account new experimental data obtained onboard spacecraft studying outer regions of the solar system (Voyager 1 and 2, Pioneer 10 and 11, Hubble Space Telescope, Ulysses, SOHO and so on). Predictions and interpretations of experimental data obtained on the basis of these models are presented. Kinetic models for describing H atom motion were later suggested by Fahr et al. (Astron. Astrophys 298:587–600, 1995) and Lipatov et al. (J. Geophys. Res. 103(A9):20,631–20,642, 1998). However they were not self-consistent and did not incorporate sources to the plasma component. A self-consistent kinetic-hydrodynamic model suggested by Heerikhuisen et al. (J. Geophys. Res. 111:A06110, 2006, Astrophys. J. 655:L53–L56, 2007) was not tested on the results by Baranov and Malama (J. Geophys. Res. 111:A06110, 1993) although it was suggested much later. Besides authors did not describe in details their Monte Carlo method for a solution of the H atom Boltzmann equation and did not inform about an accuracy of this method. Therefore the results of Heerikhuisen et al. (J. Geophys. Res. 111:A06110, 2006) are in open to question and will not be considered in this review paper. That is why below we will mainly consider a progress of the Moscow group on heliospheric modelling endeavours in the kinetic-hydrodynamic approach. Criticism of the models that treat interstellar hydrogen in the heliosphere as several fluids is given. It is shown that the multi-fluid models give rise to unreal results especially for distributions of neutral component parameters. Magnetohydrodynamic (MHD) modelling of the solar wind interaction with the LISM gas is also reviewed.

Coordinated EISCAT Svalbard radar and Reimei satellite observations of ion upflows and suprathermal ions

The relationship between bulk ion upflows and suprathermal ions was investigated using data simultaneously obtained from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Reimei satellite. Simultaneous observations were conducted in November 2005 and August 2006, and 14 conjunction data sets have been obtained at approximately 630 km in the dayside ionosphere. Suprathermal ions with energies of a few eV were present in the dayside cusp region, and the ion velocity distribution changed from an isotropic Maxwellian near the cusp region to tail heating at energies above a few eV in the cusp region. The velocity distribution of the suprathermal ions has a peak perpendicular or oblique to the geomagnetic field, and the temperature of the suprathermal ions was 0.9–1.4 eV. An increase in the phase space density (PSD) of the suprathermal ions, measured with the Reimei, was correlated with bulk ion upflow observed at the same altitude using EISCAT, and with the energy flux of precipitating electrons with energies of 50–500 eV. The PSD also has a good correlation with the electron temperature, which was increased by precipitation, but not with the ion temperature (0.1–0.3 eV) at the same altitude measured with EISCAT. These results suggest that plasma waves such as broadband extremely low frequency (BBELF) wavefields associated with precipitation are connected to the bulk ion upflows in the cusp and effectively cause the heating of suprathermal ions. The heating of suprathermal ions disagrees with anisotropic heating due to O+−O resonant charge exchange.

The Sena effect

The Sena effect relates to the transport of atomic ions in a parent gas, when this transport results from the resonant charge exchange process involving ions and atoms. The physics of this process and its role in a gas discharge plasma are analyzed briefly.

Ultra-cold ion–atom collisions: near resonant charge exchange

Accurate calculations of the near resonant charge exchange cross-sections in HD+, HT+ and DT+ at very low energies are presented. The charge exchange process between an ion and its parent atom is a near resonant process that becomes inelastic when two different isotopes are involved. We find that, at very low energies, the charge exchange cross-section follows Wigner's law for inelastic processes and becomes much larger than the cross-section for elastic collisions which tends to a finite limit. The efficiency of inelastic charge exchange increases as the mass difference between the two isotopes decreases.

Theoretical aspects of energetic neutral atoms as messengers from distant plasma sites with emphasis on the heliosphere

Ions after a local charge exchange with neutral atoms are not controlled anymore by magnetic or electric fields but instead move as neutral atoms with their instantaneous velocities along free‐flight trajectories, unless they undergo further collisions of elastic or ionizing types. Atoms originating from a charge exchange process of energetic ions, so‐called energetic neutral atoms, can serve as valuable messengers of plasma sites allowing for a remote sensing of distant plasma activities. Remote diagnostics is especially enabled in the case of resonant charge exchange processes at which only charge, but nearly no momentum or energy, is exchanged between collision partners. Most important in this respect and in our context here are charge exchange collisions between protons and hydrogen atoms. In this article we review several theoretical aspects of how this context can be used to study different plasma scenarios like the solar corona and the solar wind, corotating interaction regions, planetary or cometary ionospheres, plasmaspheres or magnetospheres or like the solar wind termination shock, the heliosheath, and the outer heliospheric bow shock. In particular, we address the following questions: Where do energetic atoms play a role, and what kind of role, a dynamic or thermodynamic one, do they play there? From which plasma sites can we expect to receive energetic neutral atom fluxes including even those located far outside these sites? Though we mention in brief presently available and upcoming techniques to measure and to resolve energetic neutral atom fluxes spectrally and spatially, we put the emphasis on theoretical model calculations predicting spectral flux features of energetic neutral atoms with different origins, which in the nearest future may be observed by the NASA Small Explorer mission IBEX and, hopefully, its successors.

Charge exchange of laser-produced ions in a pulsed gas jet

Results of an experiment on the interaction of laser-produced plasma with a pulsed gas jet are reported. A resonant charge-exchange pumping of the n=3 level of the C3+ ion was observed. A spatial structure of the region of intensive interaction was obtained by a short time imaging of filtered plasma radiation. According to independent probe measurements, the interaction was realized at densities of ions and gas particles in excess of 1016 cm-3. The obtained data provide a prospect for future experiments on laser gain in the EUV spectral range based on charge-exchange pumping of the C5+ ion.

Paschen breakdown curve by one-dimensional PIC-MCC simulation

The voltage at which a gas confined in a gap ignites, i.e. the breakdown voltage, is a function of the total pressure (p) and the gap size (d). The understanding of gas discharge has been important in applications of weakly ionized plasmas and studying the properties of the plasma medium, such as nanotechnoogy, ion sources and thrusters [1-2]. We obtained the Paschen breakdown curve by considering the energy and angle dependent secondary electron emission coefficient γse for ions impinging on a MgO surface and compared it with the results of fluid simulation. For the dc breakdown, a parallel electrode assumed to be coated with MgO was considered. The gap distance between two parallel electrodes was fixed 100μm and the gas pressure varied between 100 to 1000Torr. For these simulations, Ne-Xe mixture gas was employed and an elastic, excitation and ionization collisions between electrons and neutrals as well as elastic and resonant charge exchange collisions between ions and neutrals were added to the original XPDP1 code [3]. Figure 1 shows the Paschen breakdown curves by one-dimensional PIC-MCC simulation and twodimensional fluid simulation at typical pd values used in PDP cells (1-10Torr cm). Four symbols correspond to the data from one-dimensional PIC simulation results with the energy and angle dependent γse. The solid lines were obtained using our two-dimensional fluid simulation. The constant γse used in fluid simulation are 0.2 and 0.05 for Ne and Xe ions, respectively. While the simulation results had some discrepancies, the trend of these curves is obtained. The breakdown voltage increases as the Xe content is increased and minimum voltages are shifted to higher pd values around 3Torr cm in PIC simulations [4]. The Paschen breakdown curves for Ne-Xe mixture gas have been investigated using one-

On the cross sections of resonance charge exchange of Rb, Cs, and Hg ions

The cross sections of resonance charge exchange of rubidium, cesium, and mercury ions were calculated on the basis of the experimental data on ion mobilities and the data of simulations of the collisions between ions and the atoms of their own gas in a homogeneous electric field.

Resonant charge exchange involving electronically excited states of nitrogen atoms and ions

Within the framework of the asymptotic theory the matrices for the exchange interaction potentials of the nitrogen ion, with electron shell ${p}^{2}$, and nitrogen atom, with electron shell ${p}^{3}$, are constructed. The hierarchy of interactions in the nitrogen molecular ion at large internuclear distances is constructed for different electronic states. On the basis of these interaction potentials, the cross sections of resonant charge exchange in slow collisions are evaluated for different values of electron momentum projections and then averaged over these momentum projections. The mobilities of nitrogen ions in atomic nitrogen are also derived.

Derivation of neutral oxygen density under charge exchange in the midlatitude topside ionosphere

We describe a new technique to derive neutral atomic oxygen density, [O], in the upper thermosphere using coincident incoherent scatter radar (ISR) and airglow emission observations from Arecibo Observatory. The technique exploits the nearly resonant charge exchange coupling between neutral and ionized hydrogen and oxygen that serves as the dominant chemical source and sink of protons near and above the F region peak. Under charge exchange production and loss of H+, the proton continuity equation can be solved for [O] using twilight H density profiles derived from measured H emission brightness at 656.3 nm together with ion density, temperature, and flux obtained simultaneously by the Arecibo ISR. We present both equilibrium and nonequilibrium solutions for [O] between 500 and 1500 km during a single quiescent nighttime interval under moderate solar activity. Comparisons with theoretical expectations and with MSIS‐model calculations of O density are used to identify the altitude and local time extent over which the technique is justified. These comparisons generally support technique validity between ∼600 and 800 km, where sufficient reactant densities are present to validate the charge exchange formulation of the continuity equation. Equilibrium solutions for [O] near 650–700 km exhibit excellent agreement with MSIS estimates before midnight, but deviations arising from ion transport become increasingly significant both above this height and as dawn approaches. Incorporation of measured proton flux gradients into the nonequilibrium solutions improves agreement between the derived and modeled estimates significantly after midnight, while the minor nonequilibrium contributions during several hours before midnight lend additional support for the presence of charge exchange equilibrium.

Effect of ion collisions on the parameters of dust-plasma structures

A study is made of how collisions of ions with gas atoms affect the parameters of an ion flow and the interaction between dust grains, as well as their interaction with the flow. The ion velocity distribution in a gas discharge is analyzed with allowance for both resonant charge exchange of the ions with parent gas atoms and polarizing collisions. The interaction forces between a dust grain and an ion flow and among the grains due to the charge exchange of ions with gas atoms near the grain are examined.

The problem with the non-idealness of the MHD heliosheath

When describing the plasma - field behaviour in the heliospheric interface the difficulty arises that classi- cal MHD concepts are not fully applicable to this compli- cated multifluid interaction scenario. The classical MHD concept of ideally frozen-in magnetic fields is only strictly valid, if the magnetized medium is fully ionized. As is well known, however, the heliospheric medium represents a par- tially ionized plasma which contains neutral H-atom flows interacting with the ions via resonant charge exchange pro- cesses. Caused by this cross-interaction between the neutral and the ionized media additional non-classical currents are driven which induce additional magnetic fields. These latter fields can be shown to show the tendency to diffuse relative to the ion bulk motion. As we can show this non-classical diffusion is especially pronounced near plasma boundaries or shocks and there act in a way to dissolve the abruptness in the transition structure of the plasma properties. Here we give first estimates of these effects and point to a need to re- vise the classical MHD theory at its application to partially ionized media.

Resonant charge exchange involving highly excited atoms

Transition of a classical electron between two Coulomb centers is analyzed on the basis of computer simulations. The contribution to the electron transfer cross section from a tunnel electron transition is evaluated taking into account the strong mixing of highly excited electron states due to motion of Coulomb centers. The rate of transition of a highly excited electron between two Coulomb cores with a fixed separation is evaluated together with the cross section of resonant charge exchange in slow collisions. Typical times of change of the electron momentum as a result of electron motion in the field of two Coulomb centers are determined.

Neutralization of hyperthermal Ne + on metal surfaces

Relative ion yields of low energy (320 eV) Ne + ions scattered off a number of elemental surfaces are compared. Ion survival probabilities are seen to change significantly from one element to another depending on the surface work function, suggesting that resonant charge exchange between the metal conduction band and Ne 3s atomic level may be just as important as Auger neutralization processes. The observed yield dependence on work function is qualitatively explained using a description of resonant neutralization (RN) based on the Anderson model of an atomic level near a surface. Auger processes are found to be important in determining the final charge state of outgoing ions, while quasi-resonant interactions between the core atomic levels are seen to be nonexistent.

Further evidence for formation of a narrow baryon resonance with positive strangeness in K + collisions with Xe nuclei

We have continued our investigation of the charge-exchange reaction K^+ Xe --> K^0 p Xe' in the bubble chamber DIANA. In agreement with our previous results based on part of the present statistics, formation of a narrow p K^0 resonance with mass of 1537+-2 MeV/c^2 is observed in the elementary transition K^+ n --> K^0 p on a neutron bound in the Xenon nucleus. Visible width of the peak is consistent with being entirely due to instrumental resolution and allows to place an upper limit on its intrinsic width: \Gamma < 9 MeV/c^2. A more precise estimate of the resonance intrinsic width, \Gamma = 0.36+-0.11 MeV/c^2, is obtained from the ratio between the numbers of resonant and non-resonant charge-exchange events. The signal is observed in a restricted interval of incident K^+ momentum, that is consistent with smearing of a narrow p K^0 resonance by Fermi motion of the target neutron. Statistical significance of the signal is some 7.3, 5.3, and 4.3 standard deviations for the estimators S/sqrt{B}, S/sqrt{S+B}, and S/sqrt{S+2B}, respectively. This observation confirms and reinforces our earlier results, and offers strong evidence for formation of a pentaquark baryon with positive strangeness in the charge-exchange reaction K^+ n --> K^0 p on a bound neutron.