Charge Exchange Coupling Research Articles

A physically motivated “charge-exchange method” for measuring electron temperatures within H ii regions

Aims. Temperature uncertainties plague our understanding of abundance variations within the interstellar medium. Using the PHANGS-MUSE large program, we develop and apply a new technique to model the strong emission lines arising from H ii regions in 19 nearby spiral galaxies at ~50 pc resolution and infer electron temperatures for the nebulae. Methods. Due to the charge-exchange coupling of the ionization fraction of the atomic oxygen to that of hydrogen, the emissivity of the observed [O i]λ6300/Hα line ratio can be modeled as a function of the gas phase oxygen abundance (O/H), ionization fraction (fion), and electron temperature (Te). We measure O/H using a strong-line metallicity calibration and identify a correlation between fion and [S iii]λ9069/[S ii]λ6716,6730, tracing ionization parameter variations. Results. We solve for Te and test the method by reproducing direct measurements of Te([N ii]λ5755) based on auroral line detections to within ~600 K. We apply this“charge-exchange method” of calculating Te to 4129 H ii regions across 19 PHANGS-MUSE galaxies. We uncover radial temperature gradients, increased homogeneity on small scales, and azimuthal temperature variations in the disks that correspond to established abundance patterns. This new technique for measuring electron temperatures leverages the growing availability of optical integral field unit spectroscopic maps across galaxy samples, increasing the statistics available compared to direct auroral line detections.

Analytic solution to charge-exchange source terms between Maxwellian and kappa-distributed velocity distributions in the heliosphere

Many space and astrophysical environments are dominated by magnetohydrodynamic plasma interactions that are virtually collisionless. However, pseudo-elastic collisions are present through mechanisms of ion-neutral charge-exchange. In this paper, we investigate how charge-exchange collisions affect the balance of momentum and energy between ions and neutrals within the plasma. Our primary application is the heliosphere, where the transfer of momentum and energy between protons and interstellar hydrogen ultimately modifies its shape and structure. We derive analytical formulas for charge-exchange coupling between protons with suprathermal tails, modeled as a kappa distribution, and a relatively cool population of thermal hydrogen that is moving with respect to the plasma. We discuss differences in the energy and momentum transfer rates depending on whether the plasma is modeled by a Maxwellian or kappa distribution.

Instability of the Heliopause

The heliopause (HP) separates the tenuous hot heliosheath plasma from the relatively dense cool magnetized plasma of the local interstellar medium (LISM). Fluid acceleration in the HP region can therefore drive Rayleigh-Taylor-like and Kelvin-Helmholtz- like instabilities. Charge exchange coupling of plasma ions and primary interstellar neutral atoms provides an effective gravity, suggesting the possibility of Rayleigh Taylor-like (RT-like) instabilities. Shear flow due to the velocity difference between the heliosheath and the interstellar flows drives Kelvin Helmholtz-like (KH-like) modes on the heliopause. Magnetic fields damp the classical KH instability. However, we show that energetic neutral atoms (ENAs) destabilize KH-modes,even in the presence of interplanetary and interstellar magnetic fields. We consider a model that includes a number of effects that are important in the heliosphere such as resonant change exchange between the primary neutrals and the solar wind plasma, ENAs from the inner heliosheath, plasma flows along the heliopause and magnetic fields in the inner and outer heliosheath. We find that the nose region is unstable to RT-like modes for HP parameters, while the shoulder region is unstable to a new instability that has the characteristics of a mixed RT-KH-like mode. These instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath close to the nose and shoulder regions. Whereas ENAs have a stabilizing influence on the RT instability in the vicinity of the nose region (due to counter streaming), they have a destabilizing influence on the KH instability in the vicinity of the flanks. We find that even in the presence of interplanetary and interstellar magnetic fields, ENAs can drive a new form of KH-like instability on the flanks. An analysis of the collisional and anomalous magnetic field diffusion time scales shows that ideal MHD is an appropriate model at the HP. The interstellar magnetic field therefore drapes over the HP and does not diffuse into the inner heliosheath (IHS). However, RT-like, RT-KH-like, and KH-like instabilities serve to drag outer heliosheath (OHS)/interstellar magnetic field into the IHS, allowing for local reconnection of interplanetary and interstellar magnetic field. Such reconnection may 1) enhance the mixing of plasmas across the heliopause, and 2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and easy loss of anomalous cosmic rays.

INSTABILITY OF THE HELIOPAUSE DRIVEN BY CHARGE EXCHANGE INTERACTIONS

The stability of the heliopause that separates the tenuous hot magnetized heliosheath plasma from the dense cool local interstellar magnetized plasma is examined using a fully general model that includes all the essential physical processes. Charge exchange coupling between plasma protons and primary interstellar neutral atoms provides an effective gravity that drives Rayleigh-Taylor (RT)-like instabilities. The velocity difference or shear between the heliosheath and interstellar flows, when coupled to energetic neutral atoms (ENAs), drives a Kelvin-Helmholtz (KH)-like instability on the heliopause. The shoulder region of the heliopause is unstable to a new instability that has characteristics of a mixed RT-KH-like mode. The instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath (OHS). ENAs play an essential role in driving the KH-like instability, which is fully stabilized in their absence by magnetic fields. The nonlinear phase of these instabilities is briefly discussed. We also discuss the possibility that RT-like or mixed KH-RT-like instabilities drag outer heliosheath/very local interstellar medium (OHS/VLISM) magnetic field lines into the inner heliosheath (IHS) with the VLISM flow, and the possibility that IHS and VLISM magnetic field lines experience reconnection. Such reconnection may (1) greatly enhance the mixing ofmore » plasmas across the heliopause and (2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and corresponding easy loss of anomalous cosmic rays from the heliosphere.« less

Linear modes in the partially ionized heliosphere plasma

AbstractThe heliosphere is predominantly a partially ionized plasma that consists of electrons, ions and significant neutral atoms. Nonlinear interactions among these species take place through direct collision or charge-exchange processes. These interactions modify linear and nonlinear properties of the plasma. In this work, we develop a one-dimensional linear theory to investigate linear instabilities in such a system. In our model, the electrons and ions are described by a single fluid compressible magnetohydrodynamic (MHD) model and are coupled self-consistently to the neutral fluid via compressible hydrodynamic equations. The coupling is mediated by the charge-exchange process. Based on our self-consistent analysis, we find that the charge-exchange coupling is more effective at larger length scales, and the Alfvén waves are not affected by the charge-exchange coupling. By contrast, the fast and slow waves are driven linearly unstable.

Electron orderings in the (hard‐core) boson–fermion model

AbstractThe system of coexisting local pairs and itinerant electrons described by the (hard‐core) boson–fermion model is analysed, taking into account both the intersubsystem charge exchange coupling I0 as well as the density–density interaction V0. In our preliminary report [Acta Phys. Pol. A 109, 647 (2006)] we have shown within an extended mean‐field approach that at T = 0 the model considered can exhibit not only the superconducting (SC) but also the charge density wave (CDW) phases as well as the so called charge Kondo state (CKS), which is characterised by a compensation of a local charge moment (isospin singlet). Here we shortly conclude those findings and present several new results concerning this subject. In particular the mutual stability of various phases, including the mixed ordered state (SC‐CKS) is analysed and the effects of the deviation from half‐filling on the properties of the system are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Imprints of a heliospheric bowshock on interstellar oxygen populations

It is well known that the nearby interstellar medium represents a partially ionized gas composed by dif- ferent chemical species, amongst them hydrogen, helium and oxygen as the most abundant elements. While the passage of the interstellar protons and H-atoms over the solar sys- tem has been satisfactorily well modelled meanwhile, the entrance into the heliosphere of the other interstellar chemi- cal species needs some additional care. Here we especially follow with Boltzmann-kinetic treatments the phase-space history of interstellar oxygen ions and atoms at their pas- sage over the outer heliospheric bowshock and at their fur- ther approach towards the inner heliosphere. We describe the nose region of the bowshock as a mild MHD shock of a nearly perpendicular type. While the O-atoms pass over this shock with no velocity-space imprints, by contrast the O + -ions run over the shock structure with a typical over- shoot velocity and on the downstream region are then picked up by the frozen-in magnetic fields that comove with the plasma bulk flow, i.e. the proton bulk flow. This leads to a strongly non-relaxated O-ion velocity distribution which substantially differs both from the local O-atom and pro- ton distribution functions. Due to a strong charge exchange coupling between O-ions/atoms and H-atoms/ions the dis- tributions downstream from the bowshock undergo perma- nent changes which we estimate in this study here. Even though relaxation processes operate by Coulomb collisions, wave-particle interactions and elastic atom-atom collisions, the bowshock imprints on the O- ion and atoms distribu- tion functions may be conserved throughout the whole he- liospheric interface, and, as we are going to suggest in this paper, in fact as such may be used as tracers to the physics and the nature of the bowshock. One of the main conclu- sions is that the population of O-atoms created in the vicin- ity of the bow-shock should carry a signature of the effective shock strength that could be detectable if the LIC magnetic field is about 2 microgauss or stronger.

Role of depaired electrons in superconducting ferromagnets

We consider a model for superconducting ferromagnets assuming that two types of carriers, coupled ferromagnetically and via a charge exchange coupling, give rise to superconductivity and ferromagnetism separately. The role of depaired electrons induced by intrinsic magnetism or by inhomogeneous superconductivity is analyzed assuming the coexistence of singlet superconductivity and itinerant ferromagnetism. We discuss the conditions that makes possible to get a coexistence of ferromagnetism and superconductivity.

The charge-exchange induced coupling between plasma-gas counterflows in the heliosheath

Abstract. Many hydrodynamic models have been presented which give similar views of the interaction of the solar wind plasma bubble with the counterstreaming partially ionized interstellar medium. In the more recent of these models it is taken into account that the solar and interstellar hydrodynamic flows of neutral atoms and protons are coupled by mass-, momentum-, and energy-exchange terms due to charge exchange processes. We shall reinvestigate the theoretical basis of this coupling here by use of a simplified description of the heliospheric interface and describe the main physics of the H-atom penetration through the more or less standing well-known plasma wall ahead of the heliopause. Thereby we can show that the type of charge exchange coupling terms used in up-to-now hydrodynamic treatments unavoidably leads to an O-type critical point at the sonic point of the H-atom flow, thus not allowing for a continuation of the integration of the hydrodynamic set of differential equations. The remedy for this problem is given by a more accurate formulation of the momentum exchange term for quasi-and sub-sonic H-atom flows. With a refined momentum exchange term derived from basic kinetic Boltzmann principles, we instead arrive at a characteristic equation with an X-type critical point, allowing for a continuous solution from supersonic to subsonic flow conditions. This necessitates that the often treated problem of the propagation of inter-stellar H-atoms through the heliosheath has to be solved using these newly derived, differently effective plasma – gas friction forces. Substantially different results are to be expected from this context for the filtration efficiency of the heliospheric interface.Key words. Interplanetary physics (heliopause and solar wind termination; interstellar gas) – Ionosphere (plasma temperature and density)

From localized to itinerant bipolarons in a system of bipolarons hybridized with conduction electrons

Assuming a charge exchange coupling between localized bipolarons (located in certain regions of the crystalline lattice of the high-T c cuprates) and correlated electrons (located in the CuO2 layers), the intrinsically localized bipolarons acquire itinerancy below a certain characteristic temperatureT* and condense into a superfluid state below the critical temperatureT c . The appearance of the itinerant bosonic states is linked to the opening of a pseudogap in the DOS due to strong local pairing between the conduction electrons of the electrons. As a result, the Fermi liquid properties of such a system are destroyed. These effects are manifest not only in the photoemission spectrum but also in the thermodynamic, transport, and magnetic properties.

Improved coupled-channel treatment of the (d, n̄) threshold effect

Calculations for the 90Zr(d, p) excitation function in a charge-exchange coupling model suggest that the ( d, n ) threshold effect can be explained with the resonant solution of the Lane equations taken as the proton form factor.

Evidence for charge exchange coupling inPb206(t,p)Pb208

Anomalies are observed in the excitation function of the $^{206}\mathrm{Pb}(t,p)^{208}\mathrm{Pb}$ reaction measured at 169\ifmmode^\circ\else\textdegree\fi{} lab from 9 to 16 MeV. In addition to isospin forbidden analog resonances, anomalous behavior is observed near the threshold for the analogous $t,n$ reaction. These results as well as previously reported data for other reactions are consistent with the interpretation of this latter anomaly as arising from charge exchange coupling.

Study of Charge-Exchange Coupling in Proton-Induced Reactions onMo95,98,100andZr92,94

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