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Close-coupling calculations of single (dissociative and nondissociative) and double electron capture cross sections in He[SUP2+] + H[SUB2] collisions in the range of impact energies 0.5-25 keV/amu are presented and compared with experimental data. The calculations have been carried out at the Franck-Condon level and employing both ab initio expansions, in terms of three-center electronic functions, and the independent particle model approximation. We discuss the mechanisms of the processes and the validity limits of these treatments. [ABSTRACT FROM AUTHOR]

General analytical expressions for cross sections for direct ionization in atom–atom collisions are evaluated using the classical impulse approximation. The approach is also applied to ion–atom and molecule–molecule interactions. The overall accuracy of the obtained cross sections in a broad range of energy is better, when compared with existing measurements for many collision systems, than accuracy of other analytical predictions available in literature. [ABSTRACT FROM AUTHOR]

The effect of plasma environment on the 1s → nlm charge transfer, for arbitrary n, l, and m, in proton-hydrogen collisions has been investigated within the framework of a distorted wave approximation. The effect of external plasma has been incorporated using Debye screening model of the interacting charge particles. Making use of a simple variationally determined hydrogenic wave function, it has been possible to obtain the scattering amplitude in closed form. A detailed study has been made to investigate the effect of external plasma environment on the differential and total cross sections for electron capture into different angular momentum states for the incident energy in the range of 20-1000 keV. For the unscreened case, our results are in close agreement with some of the most accurate results available in the literature. [ABSTRACT FROM AUTHOR]

The two-center atomic orbital close-coupling method is employed to study electron capture and excitation reactions in collisions of Liq+ (q=1-3) ions with ground state atomic hydrogen in the ion energy range from 0.1 keV/u to 300 keV/u, where u is the atomic mass unit. The interaction of the active electron with the projectile ions (Li+, Li2+) is represented by a model potential. Total and state-selective cross sections for charge transfer and excitation processes are calculated and compared with data from other sources when available. [ABSTRACT FROM AUTHOR]

Dependences of single-electron charge transfer cross sections on the molecule orientation are studied in collisions between α-particles and H molecules in the ground state at collision energies E from 1 to 23 keV/u. Probabilities of single-electron capture were calculated in the independent electron approximation in the context of the close coupling equation method under the assumption that the hydrogen molecule consists of two independent hydrogen pseudoatoms. The total and partial single-electron capture cross sections averaged over all orientations of the molecule well agree with available experimental data at E > 5 keV/u. [ABSTRACT FROM AUTHOR]

The mechanism of temperature bifurcation of plasma contacting surfaces due to recycling of the ionized surface material vapor is considered. It is shown that this mechanism can lead to overheating of beryllium and lithium plasma facing components (in particular, in fusion devices) prior to the thermionic electron emission mechanism. The surface temperatures and the plasma parameters, at which the considered mechanism triggers the local overheating of beryllium and lithium components, are evaluated. The increase in the surface heat load due to secondary electron emission is also considered. It is shown that the combined effects of energy and impact angle distributions of the plasma electrons can increase the averaged secondary electron emission yield to values higher than unity and can lower the average electron energy, at which such yields are achieved. [ABSTRACT FROM AUTHOR]

A simple user-friendly semiempirical model is proposed to calculate electron impact double ionization cross sections of He, Li, Li+, B+, C+, C3+, O, O2+, O3+, Ne, Ne+, Ne2+, Na, Mg, Al3+, S, and Arq+ (q=0–7) targets for the incident electron energies from threshold to 106 eV. The contributions in the total double ionization cross sections from the direct double ionization and inner-shell ionization processes are taken into account on the basis of experimental data considered. The results of the present analysis are compared with the available experimental data and theoretical calculations. The model is found successful for the description of experimental cross sections. Since, this model may be a prudent selection to meet the demand level in plasma modeling due to its simple inherent structure. [ABSTRACT FROM AUTHOR]

The relativistic eikonal approximation and a matching procedure are used to describe excitation and ionization of hydrogen-like atoms from an arbitrary discrete energy state by the impact of a highly charged relativistic bare ion. Bethe-type formulas are derived that are asymptotically valid in the limits of v → c and Z ≫ 1, where v is the relative collision velocity, c is the speed of light, and Z is the ion charge. [ABSTRACT FROM AUTHOR]

A simple empirical formula is proposed for the rapid calculation of electron impact total ionization cross sections both for the open- and closed-shell neutral atoms considered in the range 1≤ Z≤92 and the incident electron energies from threshold to about 104 eV. The results of the present analysis are compared with the available experimental and theoretical data. The proposed model provides a fast method for calculating fairly accurate electron impact total ionization cross sections of atoms. This model may be a prudent choice, for the practitioners in the field of applied sciences e.g. in plasma modeling, due to its simple inherent structure. [ABSTRACT FROM AUTHOR]

Classical Trajectory Monte Carlo method (CTMC) with the modal interaction potential [1] has been used to simulate the differential, total and partial capture cross sections in proton-oxygen atom collisions in the energy range of 0.5–200 keV. An interesting feature of the calculated differential cross sections (DCS) curve below the scattering angle 0.1○ is the presence of oscillations showing asymmetry in angular positions. The oscillations in the partial cross sections are explained in terms of swapping effect. The DCS and total cross sections are found to be in good agreement with the experimental as well as other theoretical results. [ABSTRACT FROM AUTHOR]

The Classical Trajectory Monte Carlo (CTMC) Method has been used to calculate the differential, partial and total single electron capture cross sections for the collision of H+/D+ with Ca and Mg atoms in the energy range of 1–100 keV. The differential cross sections at angles near the diffraction limit (<0.1○) in both systems show a forward peak followed by an asymptotic fall at higher angles. Total and partial capture cross sections are found to be in good agreement with the experimental observations. Oscillations in the partial capture cross sections have been explained due to the swapping of the field electron. Isotope effect in the electron transfer is reported to be negligible. [ABSTRACT FROM AUTHOR]

Post form of “boundary corrected continuum intermediate state (BCIS)” approximation has been employed to study charge transfer cross-sections in collision of Cq+, Nq+ and Oq+ (q=1–5) with ground state atomic hydrogen in the energy range of 50–200 keV/amu. In this formalism we have adopted model potential for the interaction of the active electron with the projectile ion. Calculated results for total charge transfer cross-sections have significant improvement over other existing theoretical results in their comparison to the available experimental findings except for singly charge ions. Sub-shell distribution for total charge transfer cross-section has also been reported in graphical form. Predictions suggested by Olson in connection with the sub-shell distribution of total charge transfer cross-section has been reaffirmed. However, an oscillatory structure of charge state dependence of the total charge transfer cross-sections has not been found in the present investigation. [ABSTRACT FROM AUTHOR]

In the present work, the total cross-sections for single- and double-electron-capture by low-energy highly-charged Neq+ (q =2-6) recoil ions from He atomic gas have been measured in the energy range 600–1000 eV/q. These measurements are compared with other available experimental results. The charge state dependence of the single-electron-capture cross-sections for Neq+ (q = 2-6) recoil ions incident on He at energy of 1000 eV/q is compared with the theoretical predictions of the absorbing sphere model and the classical model. [ABSTRACT FROM AUTHOR]

The differential and total cross sections for single electron capture in fast collisions of a proton with helium are examined within the four-body distorted-wave formalism. A special emphasis is given to a proper inclusion of dynamic electron-electron correlation effects. For this purpose, a new four-body quantum-mechanical model termed the Continuum Distorted Wave – Born Initial State (CDW-BIS) approximation is introduced. With regard to a previous work of Mančev [J.Phys.B 36, 93 (2003)], where the prior form of one-channel distorted wave transition amplitude was used for describing charge exchange, in the present model the dielectronic interaction V_{12}=1/r_{12}=1/|\vec r r_1- \vec r_2| explicitly appears in the perturbation potential of the post transition probability amplitude. The inclusion of the potential V_{12} is essential for the description of the Thomas projectile – _1 – e_2 scattering. Specifically, we consider asymmetric p+He collisions and the total cross sections are carried out at a large energy range from 20 to 10000 keV. The differential cross section are calculated at impact energies 400 and 630~keV. The theoretical results are compared with the available experimental data and very good agreement is found. [ABSTRACT FROM AUTHOR]

In fusion devices, strongly localized intensive sources of impurities may arise unexpectedly, e.g., if the wall is excessively demolished by hot plasma particles, or can be created deliberately through impurity seeding. The spreading of impurities from such sources both along and perpendicular to the magnetic field is affected by coulomb collisions with background particles, ionization, acceleration by electric field, etc. Simultaneously, the plasma itself can be significantly disturbed by these interactions. To describe self-consistently the impurity spreading process and the plasma response, three-dimensional fluid equations for the particle, parallel momentum, and energy balances of various plasma components are solved by reducing them to ordinary differential equations for the time evolution of several parameters characterizing the solutions in principal details: the maximum densities of impurity ions of different charges, the dimensions both along and across the magnetic field of the shells occupied by these particles, the characteristic temperatures of all plasma components, and the densities of the main ions and electrons in different shells. The results of modeling for penetration of lithium singly charged particles in tokamak edge plasma are presented. A new mechanism for the condensation phenomenon and formation of cold dense plasma structures, implying an outstanding role of coulomb collisions between main and impurity ions, is proposed. [ABSTRACT FROM AUTHOR]