Calculation of ionization within the close-coupling formalism

We present a method for calculation of differential ionization cross sections from theories that use the close-coupling expansion for the total wave function. It is shown how, from a single such calculation, elastic, excitation, and ionization cross sections may be extracted using solely the T-matrix elements arising from solution of the coupled equations. To demonstrate the applicability of this formalism, the convergent close-coupling theory is systematically applied at incident energies of 150–600 eV to the calculation of e-He ionization. Comparison with available measurements is generally very good

Close-coupling approach to electron-impact ionization of helium

The close-coupling theory of electron-impact ionization of helium is studied. It is found that the "raw" convergent close-coupling equal-energy-sharing amplitudes converge to half the required amplitudes. As in the e-H case, solving the close-coupling equations yields amplitudes that behave as results of a finite Fourier expansion of a step function. We argue that the close-coupling formalism readily solves the e-He ionization problem with equal-energy outgoing electrons at all practical incident energies, and demonstrate it at the most difficult kinematic case of 2 eV above threshold

Box-based and Laguerre-based convergent close-coupling calculations of electron–helium ionization

We apply a new implementation of the convergent close-coupling (CCC) method to electron–helium scattering. The target states are obtained from one-electron He+ box-based eigenstates rather than the usual Laguerre-based orbitals. The utility of the new method is demonstrated for 50 eV electron-impact ionization of helium with three different energy sharings between the two outgoing electrons. Excellent agreement is found between previous and new CCC predictions, and also with experimental data

Benchmark experiment and theory for near-threshold excitation of helium by electron impact

A new experimental technique has been applied to measure absolute scattering cross sections for electron impact excitation of the n ≤ 2, 3 states of helium at near-threshold energies. The experimental results are compared with predictions from recent state-of-the-art theoretical calculations. The calculations are performed using the R-matrix with pseudostates, B-spline R-matrix, and the convergent close-coupling methods. Generally, very good agreement is found between the experiment and the three theorie

Single ionization of helium by 102 eV electron impact: three-dimensional images for electron emission

Single ionization of helium by 102 eV electron impact has been studied by measuring the momentum vectors of all final-state particles, i.e., two electrons and the He + ion, with an advanced reaction microscope. Fully differential cross sections for asymmetric scattering geometry, which have been normalized to an absolute scale, have been obtained covering a large range of emission angles for the emitted low-energy (E ≤ 15 eV) electron and different scattering angles for the fast electron. Strong electron emission out of the projectile scattering plane is confirmed for electron impact, as was observed before for heavy-ion impact ionization. The data are compared with theoretical predictions from a three-Coulomb wavefunction model, first-order and second-order distorted-wave approaches, as well as a convergent close-coupling calculation

Recommended Cross Sections for Electron-Indium Scattering

20 pags., 7 figs., 6 tabs.We report, over an extended energy range, recommended angle-integrated cross sections for elastic scattering, discrete inelastic scattering processes, and the total ionization cross section for electron scattering from atomic indium. In addition, from those angle-integrated cross sections, a grand total cross section is subsequently derived. To construct those recommended cross-section databases, results from original B-spline R-matrix, relativistic convergent close-coupling, and relativistic optical-potential computations are also presented here. Electron transport coefficients are subsequently calculated, using our recommended database, for reduced electric fields ranging from 0.01 Td to 10 000 Td using a multiterm solution of Boltzmann's equation. To facilitate those simulations, a recommended elastic momentum transfer cross-section set is also constructed and presented here.The work of K.R.H., O.Z., and K.B. was supported by the United States National Science Foundation under Grant Nos. OAC-1834740 and PHY-1803844 and by the XSEDE supercomputer Allocation No. PHY-090031. The (D)BSR calculations were carried out on Stampede2 at the Texas Advanced Computing Center. The work of D.V.F. and I.B. was supported by the Australian Research Council and resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia. F.B. and G.G. acknowledge partial financial support from the Spanish Ministry MICIU (Project Nos. FIS2016- 80440 and PID2019-104727-RB-C21) and CSIC (Project No. LINKA20085). This work was also financially supported, in part, by the Australian Research Council (Project No. DP180101655), the Ministry of Education, Science and Technological Development of the Republic of Serbia, and the Institute of Physics (Belgrade).Peer reviewe

Transport of electrons and propagation of the negative ionisation fronts in indium vapour

22 pags., 23 figs.We study the transport of electrons and propagation of the negative ionisation fronts in indium vapour. Electron swarm transport properties are calculated using a Monte Carlo simulation technique over a wide range of reduced electric fields E/N (where E is the electric field and N is the gas number density) and indium vapour temperatures in hydrodynamic conditions, and under non-hydrodynamic conditions in an idealised steady-state Townsend (SST) setup. As many indium atoms are in the first metastable state at vapour temperatures of a few thousand Kelvin, the initial Monte Carlo code was extended and generalized to consider the spatial relaxation and the transport of electrons in an idealised SST experiment, in the presence of thermal motion of the host-gas atoms and superelastic collisions. We observe a significant sensitivity of the spatial relaxation of the electrons on the indium vapour temperature and the initial conditions used to release electrons from the cathode into the space between the electrodes. The calculated electron transport coefficients are used as input for the classical fluid model, to investigate the inception and propagation of negative ionisation fronts in indium vapour at various E/N and vapour temperatures. We calculate the electron density, electric field, and velocity of ionisation fronts as a function of E/N and indium vapour temperature. The presence of indium atoms in the first metastable state significantly affects the characteristics of the negative ionisation fronts. The transition from an avalanche into a negative ionisation front occurs faster with increasing indium vapour temperature, due to enhanced ionisation and more efficient production of electrons at higher vapour temperatures. For lower values of E/N, the electron density behind the streamer front, where the electric field is screened, does not decay as one might expect for atomic gases, but it could be increased due to the accumulation of low-energy electrons that are capable of initiating ionisation in the streamer interior.The work of SD, JA, DB, MSR, DS, and BPM was sup- ˇported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, and the Institute of Physics (Belgrade). The work of KRH, OZ, and KB was supported by the United States National Science Foundation under Grant Nos. OAC-1834740, PHY-1803844, and PHY-2110023, and by the XSEDE supercomputer Allocation No. PHY-090031. The work of DVF and IB, was supported by the Australian Research Council and resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia. FB and GG acknowledge partial financial support from the Spanish Ministry MICIU (Project Nos. FIS2016-80440 and PID2019-104727-RB-C21) and CSIC (Project No. LINKA20085). This work was also financially supported by the Australian Research Council (Project No. DP180101655).Peer reviewe

Electron scattering from the ground state of mercury

We give a short review of e‐Hg scattering and present some results of our recent close‐coupling calculations. We look at the challenges facing theorists in the calculation of elastic scattering and excitation of the 6s6p 1,3P1 levels