Solving close-coupling equations in momentum space without singularities for charged targets

The analytical treatment of the Green’s function in the convergent close-coupling method (Bray et al., 2016) has been extended to charged targets. Furthermore, we show that this approach allows for calculation of cross sections at zero channel energy. For neutral targets this means the electron scattering length may be obtained from a single calculation with zero incident energy. For charged targets the non-zero excitation cross sections at thresholds can also be calculated by simply setting the incident energy to the exact threshold value. These features are demonstrated by considering electron scattering on H and He+This work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Research Council, Grant DP160102106. ASK acknowledges partial support from the US National Science Foundation under Award No. PHY1415656

Calculations of electron scattering on H-like ions

Electron-impact excitation and ionization of H-like ions of nuclear charge Z = 2,..., 8 have been calculated from thresholds to high energies, with a particular focus on spin asymmetry of the cross sections. It is found that the importance of electron exchange is undiminished with increasing Z. Away from resonance regions, scaling considerations allow for accurate nonrelativistic estimates of the total-electron-spin-dependent cross sections for Z > 8.We acknowledge the Australian Research Council, and the resources and services of the National Computational Infrastructure and the Pawsey Supercomputer Centre, which are supported by the Australian and Western Australian Governments. This work also used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant No. ACI-1548562

Atomic collisional data for neutral beam modeling in fusion plasmas

The injection of energetic neutral particles into the plasma of magnetic confinement fusion reactors is a widely-accepted method for heating such plasmas; various types of neutral beam are also used for diagnostic purposes. Accurate atomic data are required to properly model beam penetration into the plasma and to interpret photoemission spectra from both the beam particles themselves (e.g. beam emission spectroscopy) and from plasma impurities with which they interact (e.g. charge exchange recombination spectroscopy). This paper reviews and compares theoretical methods for calculating ionization, excitation and charge exchange cross sections applied to several important processes relevant to neutral hydrogen beams, including H + Be4+ and H + H+. In particular, a new cross section for the proton-impact ionization of H (1s) is recommended which is significantly larger than that previously accepted at fusion-relevant energies. Coefficients for an empirical fit function to this cross section and to that of the first excited states of H are provided and uncertainties estimated. The propagation of uncertainties in this cross section in modeling codes under JET-like conditions has been studied and the newly-recommended values determined to have a significant effect on the predicted beam attenuation. In addition to accurate calculations of collisional atomic data, the use of these data in codes modeling beam penetration and photoemission for fusion-relevant plasma density and temperature profiles is discussed. In particular, the discrepancies in the modeling of impurities are reported. The present paper originates from a Coordinated Research Project (CRP) on the topic of fundamental atomic data for neutral beam modeling that the International Atomic Energy Agency (IAEA) ran from 2017 to 2022; this project brought together ten research groups in the fields of fusion plasma modeling and collisional cross section calculations. Data calculated during the CRP is summarized in an appendix and is available online in the IAEA’s atomic database, CollisionDB

Closing in on the properties of antihydrogen

Conference review, with some speculation in the closing section

Theory of electron-impact ionization of atoms

The existing formulations of electron-impact ionization of a hydrogenic target suffer from a number of formal problems including an ambiguous and phase-divergent definition of the ionization amplitude. An alternative formulation of the theory is given. An integral representation for the ionization amplitude which is free of ambiguity and divergence problems is derived and is shown to have four alternative, but equivalent, forms well suited for practical calculations. The extension to amplitudes of all possible scattering processes taking place in an arbitrary three-body system follows. A well-defined conventional post form of the breakup amplitude valid for arbitrary potentials including the long-range Coulomb interaction is given. Practical approaches are based on partial-wave expansions, so the formulation is also recast in terms of partial waves and partial-wave expansions of the asymptotic wave functions are presented. In particular, expansions of the asymptotic forms of the total scattering wave function, developed from both the initial and the final state, for electron-impact ionization of hydrogen are given. Finally, the utility of the present formulation is demonstrated on some well-known model problems

Theory of atomic ionization and the coulomb three-body breakup

An alternative surface‐integral formulation of the theory of electron‐impact ionization of atoms and the Coulomb three‐body breakup is presented

Theory of electron impact ionization of atoms

The theory of electron impact ionization of one‐ and two‐electron atoms has advanced significantly in the past two years. This paper will summarize the progress that the members of our research center have contributed to

Asymptotic form of the electron-hydrogen scattered wave

A relationship between the total wave function describing electron-impact ionization of hydrogen and the one representing scattering of two electrons and a proton in the continuum is revealed. On the basis of this relationship, forms of the scattered wave for the ionization process valid in all asymptotic domains are obtained. When all interparticle distances become large, the new wave functions reduce to the well-known Peterkop asymptotic wave function obtained in the hyperspherical approach. In particular, the Peterkop wave function is obtained by direct application of the present approach. This allows one to resolve the long-standing amplitude-phase ambiguity problem, which is an artifact of the hyperspherical approach to the ionization process. The Peterkop wave function is invalid when the two electrons are close to each other. This causes problems in practical calculations even in the domain where all particles are far apart. Our formulation provides a solution to this problem

Integral representation for the electron-atom ionization amplitude which is free of ambiguity and divergence problems

The problems related to the formal theory of electron-atom ionization were studied. An integral representation for the ionization amplitude, which was free of ambiguity and divergence problems, was presented. Electron impact ionization of atomic hydrogen was considered, and it was assumed that the proton was infinitely heavy compared to the electrons and remained at rest. The results show that the proposed representation is readily applicable to extract the exact breakup amplitudes in direct calculations of general few-body systems