Influence of nuclear multiple scattering on axially channeled protons in a bent crystal

The influence of nuclear multiple scattering on axially channeled protons with an energy of 7 TeV through a bent Si crystal, is presented in this paper. The aims of the investigation are the processes correlated to the axial channeling, such as dechanneling, angular distributions and energy loss distribution. The data for these processes are generated via the numerical solution of the proton equations of motion in the transverse plane and the computer simulation method. In the simulations, the crystal thickness is varied from 1 to 5 mm while the bending angle is varied from 0 to 20 μrad. The increasing of the transverse energy of axially channeled protons is due to its multiple scattering by atomic strings and the bending dechanneling mechanism. The analysis of the generated data shows that in the cases we are considering, the dechanneling function, the energy loss spectra, and the angular distributions do not undergo to any significant changes when the effect of nuclear multiple scattering is included in the ion-atom interactions. © 2018, Vinca Inst Nuclear Sci. All rights reserved

Electron capture, excitation and ionization processes in He

Electron capture, excitation and ionization processes in He2+–H collisions taking place in quantum plasmas are studied by employing the two-center atomic orbital close coupling (TC-AOCC) method. The Debye-Hückel-cosine (DHC) potential is used to describe the plasma screening effects on the Coulomb interaction between charged particles. The properties of eigenenergies of hydrogen-like atom with DHC potential are investigated as function of the screening length of the potential. It is found that the binding energies of nl states decrease with decreasing the screening length of the potential. The dynamics of excitation, electron capture and ionization processes in He2+–H collision system is investigated when the screening length of the potential varies for a wide collision energy range. The TC-AOCC cross sections are compared with those for the pure Coulomb potential and, for the total electron capture, with the results of classical trajectory Monte Carlo method

Alignment of H(2p) in collisions of protons and antiprotons with hydrogen atoms with screened Coulomb interaction

The effects of screened Coulomb interaction on the alignment of H(2p) state produced in collisions of hydrogen atoms with protons and antiprotons are investigated in the energy range 1–200 keV by using the two-center atomic orbital close-coupling (TC-AOCC) method. It is shown that the decrease of the binding energy of hydrogen nl-states and the reduction of the number of bound states with increasing the strength of the screening affect significantly the alignment degree and its energy dependence. In the case of antiproton-H collision the difference between the alignments with screened and unscreened Coulomb potential increases with increasing the strength of the screening in the entire energy range above 2 keV/u, while in the case of proton-H collision it does so only in the energy range 5–25 keV/u

Cross sections for electron capture and excitation in proton collisions with the metastable Be(2s2p

The two-center atomic orbital close-coupling method is employed to study electron capture and excitation processes in proton collisions with the metastable Be(1s2s2p P) atom. The interaction of the active electron with the Be ion core is represented by a model potential reproducing accurately (to within 3.5%) the energies of triplet excited states Be(1s2snl L) (at least up to n = 7). The excitation and state-selective electron capture cross sections up to the n = 5 shells of both centers are calculated in the energy range 1–200 keV/u using an expansion basis involving all the states with n ≤ 7 on H and all triplet states with n ≤ 7 on Be, augmented with a number of pseudostates. In the energy region below ~10 keV/u, the cross sections of both processes exhibit oscillatory structures, resulting from the multistate coupling accounted for in the dynamical model. It has been found that the magnitude of excitation cross sections above ~10 keV/u is dominated by the multipole interactions, while below this energy the excitation process proceeds through intermediate electron capture states

Electron capture and excitation in H

The processes of state-selective electron capture and excitation in proton collisions with Li+(1s2 1S) and Li+(1s2s 1,3S) ions are studied by using the two-center atomic orbital close-coupling (TC-AOCC) methods in the energy range 2.5–800 keV. The interaction of the active electron with the Li2+ ion core is represented by model potentials that reproduce the energies of excited singlet and triplet states of Li+ with accuracy better than 2%. The expansion basis in the coupled state calculations includes all states with n ≤ 8 (in total 120 states) centered on each of the colliding centers. Total and state-selective electron capture and excitation cross sections to final states with n ≤ 4 are presented. The physical mechanisms involved in the dynamics of considered processes are discussed in detail. The reported cross sections should be useful in the kinetic modeling and diagnostics of fusion reactor plasmas with liquid lithium divertors

Influence of nuclear multiple scattering on axially channeled protons in a bent crystal

The influence of nuclear multiple scattering on axially channeled protons with an energy of 7 TeV through a bent Si crystal, is presented in this paper. The aims of the investigation are the processes correlated to the axial channeling, such as dechanneling, angular distributions and energy loss distribution. The data for these processes are generated via the numerical solution of the proton equations of motion in the transverse plane and the computer simulation method. In the simulations, the crystal thickness is varied from 1 to 5 mm while the bending angle is varied from 0 to 20 mrad. The increasing of the transverse energy of axially channeled protons is due to its multiple scattering by atomic strings and the bending dechanneling mechanism. The analysis of the generated data shows that in the cases we are considering, the dechanneling function, the energy loss spectra, and the angular distributions do not undergo to any significant changes when the effect of nuclear multiple scattering is included in the ion-atom interactions

Antiproton-impact ionization of hydrogen atom with Yukawa interaction

The process of ionization of hydrogen atom by antiproton impact is studied when the interparticle interactions in the system are described by screened interactions of Yukawa type. The collision dynamics is described by the semiclassical atomic-orbital close-coupling method in which the bound atomic states and positive energy continuum pseudostates are determined by diagonalization of target Hamiltonian in a sufficiently large even-tempered basis to ensure convergence of the results at each value of the screening length λ of the interaction. With decreasing the screening length, the bound states in the Yukawa potential become unbound, thus increasing the number of continuum pseudostates. At low collision energies, this leads to the increase of the ionization cross section. It is observed that the energies of pseudostates, generated by the exit of nl bound states in the continuum, at certain critical values λnlc exhibit series of avoided crossings when λ is varied. The avoided crossings appear between the (n + k) l and (n + k + 1) l (n = 1, 2, 3, … ; k = 0, 1, 2, …) states at screening lengths close to the critical screening length λnlc. The avoided crossings become increasingly less pronounced with increasing n, k and l. The matrix elements for the (n + k) l - (n + k + 1) l transitions at the avoided crossings λx,(n+k)l(n+k+1)l exhibit maxima and are reflected in the structure of the cross sections for population of the lower nl pseudostates. These structures are, however, smeared out in the total ionization cross section