Viacheslav Shevelko

Stripping of fast heavy low-charged ions in gaseous targets

Abstract Projectile-ionization (stripping) cross-sections and beam lifetimes have been calculated for heavy low-charged ions of Pb, Bi and U colliding with H, He, Be, Li, F, N, Ar and Xe atoms in the E =1–100 MeV/u energy range. Calculations have been performed for single-electron processes in the Born approximation using the LOSS computer code accounting for the atomic structure of the target. Results are compared with available experimental data, CTMC calculations and Z 2 + Z scaling where Z is the nuclear charge of the target atom. In the case of Pb-like ions (Pb 0+ ,Bi 1+ ,…,U 10+ ), the scaling law for the stripping cross-sections on the projectile charge and the target nuclear charge is obtained. In the energy range considered, the calculated cross-sections are proportional to Z 1.4 due to the screening of the target nucleus by its electrons which differs markedly from the Z 2 -dependence given by the first-order perturbation theory. The role of multi-electron processes is briefly discussed.

Dipole Transitions in Atoms and Ions With One Valence Electron

Oscillator strengths, atomic transition probabilities and photoionisation cross-sections have been calculated for alkali-like atoms and ions, i.e., for atomic systems with one valence electron outside the spherical core. Calculations have been performed in one-electron approximation with allowance for polarisation of the core by an external electric monochromatic field. The including of this effect leads to a change of the matrix element r to r-q, where q describes the induced dipole moment of the core. The polarisation effect strongly influences on the ratio of doublet in the principal series f3/2/f1/2, on the behaviour of the photoionisation cross sections (including inner shells) and the excitation cross sections for optical transitions induced by electron impact. Numerical calculations have been made for the atoms Li I, Na I, K I, Cu I, Rb I, Cs I, Ag I, Au I and ions Mg II, Al III, Ca II, Zn II, Ga III, Sr II, Cd II, In III, Ba II and Hg II.

Static Dipole Polarizability of Atoms and Ions in the Thomas-Fermi Model

A statistical theory of the dipole polarizability α is given for atoms and ions, described in the Thomas-Fermi model. A universal dependence of the polarizability of atoms and ions on their radius is constructed by numerical calculations. In the case of multiply-charged ions the expression for α has a simple analytical form. The results of the computation are in good agreement with available experimental and theoretical data especially when the outer electron shells are more than half-filled.

Atomic processes in basic and applied physics

Laboratory and astrophysical plasmas. Modern view on ball lightning: Observations, experiments, theories V. Bychkov and A.Nikitin.-Unravelling the mysteries of matter surrounding supermassive black holes A. Muller and S. Schippers.- Spectroscopic diagnostics of hot coronal plasma A.M.Urnov.- Hot spots and giant spiders clouding the solar sky S.V.Kuzin and A.M. Urnov.- Populations of excited parabolic states of hydrogen beam in fusion plasmas O. Marchuk et al.- Atomic processes in dusty plasmas Young-Dae Jung.- Atomic and Molecular Data Need for Industrial Application Plasmas J.-S. Yoon et al.- Atomic collisions. Charge transfer dynamics in low to intermediate energy ion-atom/molecule collisions studied by momentum imaging techniques X. Ma et al.-Single and Multiple Electron Loss by Heavy Ions R. DuBois and T. Santos.-Target-density effects in atomic collisions V.P. Shevelko and H. Tawara.- Excitation and ionization in atom-atom collisions A.D. Ulantsev.- Atomic collisions in liquid targets A. Itoh.- Excited states of atomic hydrogen in reflected neutrals at high-Z metal surfaces D.Kato.- The long-range interaction effects in collisions of Rydberg atoms with neutral targets V.S. Lebedev and A.A. Narits.- Useful formula and Internet resources for ionic collisions A.M. Imai and D. Humbert .- Applications. Atomic Processes and Data Requirements in Tumor Therapy T. Kanai.- Atomic X-Ray Physics at the Experimental Storage Ring ESR H.Beyer et al. Atomic physics using highly intense X-ray pulses M. Martins et al.- Cascade of atomic displacements with account for ion-ion cross sections in solid state O.V. Ivanov and A.V. Subbotin.- Approach to ultra-low ion beam temperatures by beam cooling A. Noda et al.- Nonlinear and multipole effects on optical lattice clock V.D. Ovsiannikov et al.- Photorecombination of highly charged heavy ions Ch.Kozhuharov and C. Brandau.-References Index.

K-shell ionization of free metal atoms K, Ca, Rb and Sr by electron impact

Absolute cross sections for K-shell ionization of free metal atoms K, Ca, Rb and Sr by electrons with energies up to 45 keV have been measured with uncertainty ± 15% using a crossed-beams technique. The results are compared with other measurements for free atoms and theoretical calculations.

The energy-deposition model: electron loss of heavy ions in collisions with neutral atoms at low and intermediate energies

Single- and multiple-electron loss processes of heavy many-electron ions (positive and negative) in collisions with neutral atoms at low and intermediate energies are considered using the energy-deposition model. The DEPOSIT computer code, created earlier to calculate electron-loss cross sections at high projectile energies, is extended for low and intermediate energies. A description of a new version of the DEPOSIT code is given, and the limits of validity for collision velocity in the model are discussed. Calculated electron-loss cross sections for heavy ions and atoms (N+, Ar+, Xe+, U+, U28+, W, W+, Ge−, Au−), colliding with neutral atoms (He, Ne, Ar, W), are compared with the available experimental and theoretical data at energies E > 10 keV/u. It is found that in most cases the agreement between the experimental data and the present model is within a factor of 2. Combining results obtained by the DEPOSIT code at low and intermediate energies with those by the LOSS-R code at high energies (relativistic Born approximation), recommended electron-loss cross sections in a wide range of collision energy are presented.

Charge-changing collisions of tungsten and its ions with neutral atoms

New experimental and theoretical data on charge exchange (CE) cross sections are presented for low-energy collisions (10?500?eV u?1) of W+ and W2 + ions with H, H2 and He atoms. The CE cross sections are calculated using the ARSENY code based on the hidden crossing method. The isotope effect (mass dependence) in collisions of W+ and W2 + ions with hydrogen isotopes H, D, T is studied in the framework of the adiabatic theory of transitions in slow collisions. Furthermore, the electron loss (EL) and CE cross sections for the energy range of 1?105 keV u?1 are calculated for tungsten and its ions Wq + (q = 0?40) colliding with H, He, N, Ar and W atoms using the computer codes (CAPTURE, DEPOSIT and RICODE) based upon the Born approximation and the classical energy-deposition model. The data obtained can be used for plasma modelling, planning and interpretation of future experiments in fusion devices using tungsten as a material for the plasma-facing components.

Density-dependent Lines of One- and Two-electron Ions in Diagnostics of Laboratory plasma. I.The rates of collision relaxation of excited levels

Plasma devices with inertial plasma confinement such as laser produced plasmas, exploding wires, plasma focus, etc., which have been rapidly developed during recent years, appear to be very intensive sources of spectral line radiation in far UV and X-ray regions. Analysis of this radiation provides a good tool for plasma diagnostics with very high electron densities up to 1022 cm-3. In this work, consisting of two parts, we consider the mechanism of the formation of spectral lines in hot and dense plasma. The key point for density diagnostics is the fact that for some ion levels the rate of collisional relaxation has the same order of magnitude as the radiative decay. Thus the intensities of spectral lines arising from these levels show a strong dependence on electron density which makes diagnostics possible. In the first paper, emphasis is laid on the calculation of rates of transition between close ion levels induced by electron or ion impact, which usually gives the main contribution to the collisional relaxation constants. The influence of plasma polarization effects on the collision frequency in a dense plasma is also considered. In a second paper, the formation of spectral lines of hydrogen-like, helium-like and oxygen-like ions will be considered for electron density 1018 cm-3 ≤ N ≤ 1024 cm-3 and the ion charge 10 ≤ Z ≤ 19.

Influence of theTarget — Density Effects on Electron — Capture Processes

The influence of the target density on the electron‐capture (EC) processes in collisions of fast ions with atoms and molecules is considered. The partial EC cross sections σn on the principal quantum number n of the scattered projectile, as well as the total σtot values are calculated for highly charged ions interacting with gaseous and solid targets in the energy range of E = 100 keV/amu to 10 MeV/amu. It is shown that with the target density increasing, the population of the excited states of the scattered projectiles, formed via the EC channel, is suppressed due to projectile ionization by the target particles and, as a result, the effective EC cross sections drastically decrease.

Electron Loss and Capture Processes in Collisions of Heavy Many-Electron Ions with Neutral Atoms

The present status and properties of charge-changing processes—electron capture and electron loss—are considered for heavy many-electron ions colliding with neutral atoms over a wide energy range E = 10 keV/u–100 GeV/u. The role of single- and multiple-electron charge-changing processes is discussed, and a brief description of available computer codes for calculation of the corresponding cross sections is presented. Experimental data for electron-loss and capture cross sections for germanium, xenon, lead, and uranium ions colliding with H, N, Ne, Ar, and Xe targets are given in comparison with numerical calculations applying different theoretical models as well as semiempirical formulae.