Enhanced Balmer-[MATH] emission in interpenetrating plasmas

The DUET Collaboration reports on the measurements of the absorption ($\sigma_{\mathrm{ABS}}$) and charge exchange ($\sigma_{\mathrm{CX}}$) cross sections of positively charged pions on carbon nuclei for the momentum range 201.6 MeV$/c$ to 295.1 MeV$/c$. The uncertainties on the absorption and charge exchange cross sections are $\sim$9.5\% and $\sim$18\%, respectively. The results are in good agreement with previous experiments. A covariance matrix correlating the 5 $\sigma_{\mathrm{ABS}}$ and 5 $\sigma_{\mathrm{CX}}$ measured data points is also reported

The energy dependence of the total cross section for symmetric charge exchange in helium is measured in the range from 400-2000 eV. Beam-attenuation techniques are used, and all measurements are made on the forward-scattered ions and the high-energy neutrals resulting from the charge exchange. Cross-section values are given at 100-eV intervals, and the results show a cross section decreasing as the energy increases, with a value at 1000 eV of 1.04 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$. The absolute cross sections are accurate to \ifmmode\pm\else\textpm\fi{} 12%. Relative cross-section values accurate to \ifmmode\pm\else\textpm\fi{} 6% are reported.

The authors calculate the differential cross sections for charge exchange at high energies by means of the continuum-distorted-wave (CDW) approximation. The calculations show the importance of contributions from second-order terms in the electron-nucleus interaction for both the magnitude of the cross section and its variation with angle. The internuclear repulsion is included exactly within a first-order expansion in the ratio of the electron to proton mass. Comparisons are made with recent experimental data on H+-He and H+-Ar collisions.

theoretical rate equations in order to determine the average charge exchange rates. These rates were compared to charge exchange rates of an ion with a known charge exchange cross section (Ar{sup 11+}) measured in a similar manner in order to determine the average charge exchange cross sections for the highly charged ions. The energy of interaction between the highly charged ions and hydrogen was estimated to be 4 eV in the center of mass frame. The mean charge exchange cross sections were 9 {times} 10{sup {minus}14} cm{sup 2} for Xe{sup 43+} to Xe{sup 46+} and 2 {times} 10{sup {minus}13} cm{sup 2} for Th{sup 73+} to Th{sup 79+}. Double capture was approximately 20--25% of the total for both xenon and thorium. A fit indicated that the cross sections were approximately proportional to q. This is consistent with a linear dependence of cross section on q within the measurement uncertainties.

Summary form only given. A number of critical ionization velocity (CIV) experiments have been performed in space. CIV has been observed in laboratory experiments, but experiments in space have been inconclusive. Most space experiments have used barium which ionizes easily, and with emission lines from both neutrals and ions in the visible optical observations can be made from the ground. High initial ionization in some barium release experiments has been claimed due to CIV. However, a number of reactions between barium and the ambient plasma have been suggested as more likely processes. Currently the most popular process in this debate is charge exchange with O/sup +/. This process has a large cross section, but the question is whether it is large enough. The cross section for charge exchange with calcium should be even larger, but in a double release of barium and calcium (part of the NASA Combined Release and Radiation Effects Satellite release experiments) most ionization was observed from the barium release. Moreover, if charge exchange is the dominant process, the amount of ionization should relate to the oxygen ion density, and that does not appear to be the case.

In the heliosphere, especially in the inner heliosheath, mass-, momentum-,\nand energy loading induced by the ionization of neutral interstellar species\nplays an important, but for some species, especially Helium, an underestimated\nrole. We discuss the implementation of charge exchange and electron impact\nprocesses for interstellar neutral Hydrogen and Helium and their implications\nfor further modeling. Especially, we emphasize the importance of electron\nimpact and a more sophisticated numerical treatment of the charge exchange\nreactions. Moreover, we discuss the non-resonant charge exchange effects. The\nrate coefficients are discussed and the influence of the cross-sections in the\n(M)HD equations for different reactions are revised as well as their\nrepresentation in the collision integrals. Electron impact is in some regions\nof the heliosphere, particularly in the heliotail, more effective than charge\nexchange, and the ionization of neutral interstellar Helium contributes about\n40% to the mass- and momentum loading in the inner heliosheath. The charge\nexchange cross-sections need to be modeled with higher accuracy, especially in\nview of the latest developments in their description. The ionization of Helium\nand electron impact ionization of Hydrogen needs to be taken into account for\nthe modeling of the heliosheath and, in general, astrosheaths. Moreover, the\ncharge exchange cross-sections need to be handled in a more sophisticated way,\neither by developing better analytic approximations or by solving the collision\nintegrals numerically.\n

Highly charged xenon (35+ to 46+) and thorium (72+ to 79+) ions were produced in an Electron Beam Ion Trap (EBIT). The ions were extracted from EBIT in a short pulse. Ions of one charge state were selected using an electromagnet. The ions were recaptured at low energy in a cryogenic Penning trap (RETRAP). As the ions captured electrons from molecular hydrogen, populations of the various charge states were obtained by measuring the image currents induced by the ions on the electrodes of the trap. Data on the number of ions in each charge state vs. time were compared to theoretical rate equations in order to determine the average charge exchange rates. These rates were compared to charge exchange rates of an ion with a known charge exchange cross section (Ar{sup 11+}) measured in a similar manner in order to determine the average charge exchange cross sections for the highly charged ions. The energy of interaction between the highly charged ions and hydrogen was estimated to be 4 eV in the center of mass frame. The mean charge exchange cross sections were 9 {times} 10{sup {minus}14} cm{sup 2} for Xe{sup 43+} to Xe{sup 46+} and 2 {times} 10{sup {minus}13} cm{sup 2} for Th{sup 73+} to Th{sup 79+}. Double capture was approximately 20--25% of the total for both xenon and thorium. A fit indicated that the cross sections were approximately proportional to q. This is consistent with a linear dependence of cross section on q within the measurement uncertainties.

The proportion of N4+ photofragmenting to yield N2+ in X 2Σg+v≳0 states has been measured by observing the yield of the fragments’ charge transfer reaction with Ar. Such a determination is possible because N2+ in the v=0 level has a cross section for charge exchange with Ar that is 2 orders of magnitude smaller than in higher vibrational levels. The fraction of N2+(v≳0) fragments increases from 0.30 at 620 nm to 0.37 at 266 nm. Calculations, which treat the N2+ and N2 fragments as quantum harmonic oscillators and the dissociation coordinate classically, predict an N2+ fragment vibrational content that is of the same order as that observed. The substantial population of vibrationally quiescent N2+ fragments, along with previous kinetic energy release studies of N4+ photodissociation, that show a limited fraction of the available energy appears as translational motion [M. F. Jarrold, A. J. Illies, and M. T. Bowers, J. Chem. Phys. 81, 214 (1984)], suggest that the fate of much of the photon’s energy is either in product rotational motion or in the neutral N2 vibration. Mechanisms for the dissociation are discussed.

For pt.I see ibid., vol.24, no.18, p.4049-60 (1991). The authors report a treatment of slow C3++H collisions for impact energies E=0.04-9 keV amu-1, using an expansion in terms of 22 molecular states modified with a common translation factor. Calculated partial and total cross sections for charge exchange are in good agreement with measured ones. Cross sections and values for the alignment parameter for C3+ excitation are predicted. A detailed study of the collision dynamics is presented.

The physics of multicharged ions has considerably developed during the last years1. Aside from purely academic and fundamental interest, the initial motivation arose from fusion research. Indeed from simple theoretical arguments it could be predicted that cross sections for charge exchange between highly charged impurities present in tokomak devices, and hydrogen atom would be very large (10-15–10-14 cm2). Knowledge of the plasma properties would therefore require measurement of the corresponding cross sections as well as a better understanding of the collision process. A large number of experiments were therefore undertaken to determine the total (all processes included) electron capture cross section for a variety of multicharged ions. In contrast, very little work was devoted to the identification of the states which are effectively populated by the collision process. A similar effort was undertaken in theory, for the collision energy range of interest for nuclear fusion (say few keV/Nucleon). At these energies the electron velocity v is much larger than the collision velocity V so that the electron motion adapts itself adiabatically (or quasi-adiabatically) to the nuclear motion as in a molecule.

X-ray emission from a comet was observed for the first time in 1996. One of the mechanisms believed to be contributing to this surprisingly strong emission is the interaction of highly charged solar wind ions with cometary gases. Reported herein are total absolute charge-exchange and normalized line-emission (X-ray) cross sections for collisions of high-charge state (+3 to +10) C, N, O, and Ne ions with the cometary species H2O and CO2. It is found that in several cases the double charge-exchange cross sections can be large, and in the case of C3+ they are equal to those for single charge exchange. Present results are compared to cross section values used in recent comet models. The importance of applying accurate cross sections, including double charge exchange, to obtain absolute line-emission intensities is emphasized.

A previous study of charge exchange processes taking place through ionic–covalent transitions is extended to the case of Na+H and Na++H− collisions. A five-state molecular expansion, with the inclusion of two-electron translation factors, is employed to calculate the charge exchange and neutralization cross sections. Transitions at the first two pseudocrossings between the energy curves, practically determine the cross sections in the energy range 0.16–5 keV amu−1. We also show that the widely used multichannel Landau–Zener theory is totally inadequate, to treat these transitions.

Nuclear continuum charge exchange of hadrons at [formula omitted

Heavy-ion charge exchange in the eikonal approximation

The A dependence of the forward cross section for inclusive pion double charge exchange on nine target nuclei from 6Li to 209Bi at T0 = 0.59 GeV, as well as the cross section for 6Li, 7Li, and 12C nuclei at T0 = 0.59, 0.75, and 1.1 GeV, was measured with the 3-m magnetic spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The resulting A dependence is well described within the model involving two sequential single charge exchanges and taking into account the renormalization of the amplitude for pion single charge exchange in a nucleus. A relatively weak energy dependence of the cross section for the 6Li, 7Li, and 12C nuclei agrees with the analogous dependence obtained previously for the 16O nucleus, but it contradicts the predicted sharp decrease in the cross section within the model involving two sequential single charge exchanges. This result provides an additional piece of evidence that the contribution from the mechanism of inelastic Glauber rescattering is significant at T0 ≳ 0.6 GeV.