Multiple-electron losses of highly charged ions colliding with neutral atoms

We present calculations of the total and m-fold electron-loss cross sections using the DEPOSIT code for highly charged U(q+) ions (q=10,31,33) colliding with Ne and Ar targets at projectile energies E=1.4 and 3.5 MeV/u. Typical examples of the deposited energy T(b) and m-fold ionization probabilities Pm(b) used for the cross-section calculations as a function of the impact parameter b are given. Calculated m-fold electron-loss cross sections are in a good agreement with available experimental data. Although the projectile charge is rather high, a contribution of multiple-electron loss cross sections to the total electron-loss cross sections is high: about 65% for the cases mentioned.Comment: 6 pages, 4 figure

Symmetric eikonal model for projectile-electron excitation and loss in relativistic ion-atom collisions

At impact energies $\stackrel{>}{\sim}1$ GeV/u the projectile-electron excitation and loss occurring in collisions between highly charged ions and neutral atoms is already strongly influenced by the presence of atomic electrons. In order to treat these processes in collisions with heavy atoms we generalize the symmetric eikonal model, used earlier for considerations of electron transitions in ion-atom collisions within the scope of a three-body Coulomb problem. We show that at asymptotically high collision energies this model leads to an exact transition amplitude and is very well suited to describe the projectile-electron excitation and loss at energies above a few GeV/u. In particular, by considering a number of examples we demonstrate advantages of this model over the first Born approximation at impact energies $\sim 1$--30 GeV/u, which are of special interest for atomic physics experiments at the future GSI facilities.Comment: 14 pages, 5 figure

Charge-exchange collisions in interpenetrating laser-produced magnesium plasmas

Abstract Charge-exchange collisions are one of the effective pumping methods for soft X-ray lasers. Experiments are performed to investigate charge-exchange collisions between highly charged Mg ions in colliding laser-produced magnesium plasmas. Pinhole photography and XUV spectroscopy are used as diagnostic tools. Spectroscopic studies show selective population of n ϭ 3 levels of Mg IX ions, which results in enhancement of respective line intensities. Theoretical calculations also give a large cross section as high as 10 Ϫ15 cm 2 for these charge-exchange collisions when the relative velocities of the colliding ions are of the order of 10 7 cm s Ϫ1 . XUV pinhole pictures are taken in early stages, which give more insight into the expansion dynamics of the colliding magnesium plasmas

Ionization of highly charged relativistic ions by neutral atoms and ions

Ionization of highly charged relativistic ions by neutral atoms and ions is considered. Numerical results of recently developed computer codes based on the relativistic Born and the equivalent-photon approximations are presented. The ionization of the outer shells dominate. For the outer projectile electron shells, which give the main contribution to the process, the non-relativistic Schr\"odinger wave functions can be used. The formulae for the non-relativistic reduction of the Dirac matrix-elements are obtained for ionization of electrons with arbitrary quantum numbers $n$ and $\ell$.Comment: 7 pages, 3 figure

Quantum-mechanical calculation of Stark widths of Ne VII n=3, Δn=0\Delta n=0 transitions

The Stark widths of the Ne VII 2s3s-2s3p singlet and triplet lines are calculated in the impact approximation using quantum-mechanical Convergent Close-Coupling and Coulomb-Born-Exchange approximations. It is shown that the contribution from inelastic collisions to the line widths exceeds the elastic width contribution by about an order of magnitude. Comparison with the line widths measured in a hot dense plasma of a gas-liner pinch indicates a significant difference which may be naturally explained by non-thermal Doppler effects from persistent implosion velocities or turbulence developed during the pinch implosion. Contributions to the line width from different partial waves and types of interactions are discussed as well.Comment: 8 pages, 3 figures; accepted by Phys. Rev.

Electron Impact Excitation Cross Sections for Hydrogen-Like Ions

We present cross sections for electron-impact-induced transitions n --> n' in hydrogen-like ions C 5+, Ne 9+, Al 12+, and Ar 17+. The cross sections are computed by Coulomb-Born with exchange and normalization (CBE) method for all transitions with n < n' < 7 and by convergent close-coupling (CCC) method for transitions with n 2s and 1s --> 2p are presented as well. The CCC and CBE cross sections agree to better than 10% with each other and with earlier close-coupling results (available for transition 1 --> 2 only). Analytical expression for n --> n' cross sections and semiempirical formulae are discussed.Comment: RevTeX, 5 pages, 13 PostScript figures, submitted to Phys. Rev.

Stark Broadening of the B III 2s-2p Lines

We present a quantum-mechanical calculation of Stark line widths from electron-ion collisions for the $2s_{1/2}-2p_{1/2,3/2}$, lambda = 2066 and 2067 A, resonance transitions in B III. The results confirm the previous quantum-mechanical R-matrix calculations but contradict recent measurements and semi-classical and some semi-empirical calculations. The differences between the calculations can be attributed to the dominance of small L partial waves in the electron-atom scattering, while the large Stark widths inferred from the measurements would be substantially reduced if allowance is made for hydrodynamic turbulence from high Reynolds number flows and the associated Doppler broadening.Comment: 21 pages, 4 figures; to be published in Phys. Rev.

Electron impact excitation cross sections for allowed transitions in atoms

We present a semiempirical Gaunt factor for widely used Van Regemorter formula [Astrophys. J. 136, 906 (1962)] for the case of allowed transitions in atoms with the LS coupling scheme. Cross sections calculated using this Gaunt factor agree with measured cross sections to within the experimental error.Comment: RevTeX, 3 pages, 10 PS figures, 2 PS tables, submitted to Phys. Rev.