Influence Of Multiple Ionization Research Articles

Influence of Multiple Ionization on Charge State Distributions

SynopsisWe describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. Previous ionization balance calculations have largely neglected EIMI. Here, EIMI cross-section data are incorporated into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.

K-shell ionization by low-energy 14N ions

K-shell ionization by slow, heavy projectiles has been studied for moderately asymmetric ( Z 1/ Z 2 ∼ 0.3) collisions by measuring K-X-ray production cross sections in Ca, Sc, Ti, Cr, Fe and Cu excited by 14N ions of energy 1.75–3.15 MeV. The influence of multiple ionization in L- and M-shells on measured data was estimated by analyzing K-X-ray energy shifts and K β/K α intensity ratios. The results are compared with the predictions of K-shell ionization theories, based on the plane-wave Born approximation (PWBA), semiclassical approximation (SCA), binary-encounter approximation (BEA), and adiabatic molecular orbital (MO) approach. Different corrections to these approaches, to account for the higher-order effects, are discussed. The data are not satisfactorily described in detail by discussed theories over the whole energy range, but the SCA calculations reproduce the present, low-energy data quite reasonably. The need for a more realistic description of the electron binding effect is discussed.

L-subshell ionization of heavy elements by carbon and nitrogen ions of energy 0.4-1.8 MeV/amu.

L-shell x-ray production and subshell ionization cross sections have been measured for 0.4--1.8-MeV/amu carbon and nitrogen ions for selected heavy elements with 72\ensuremath{\le}${\mathit{Z}}_{2}$\ensuremath{\le}90. The results are compared with the predictions of the ECPSSR theory [perturbed-stationary-state (PSS) theory with energy-loss (E), Coulomb deflection (C), and relativistic (R) corrections] describing both direct ionization and electron-capture processes and the semiclassical approximation (SCA) calculations for direct ionization. For both theories significant deviations are found for ${\mathit{L}}_{2}$-subshell ionization in the low-energy range. The multiple ionization of outer shells was studied by comparing L x-ray intensity ratios measured for heavy ions and protons. The ionization probabilities of the ${\mathit{N}}_{4}$ subshell at zero impact parameter was extracted from these data. Measured ionization probabilities are compared with the predictions of the SCA theory and the ``geometrical model.'' The influence of multiple ionization on the measured L-subshell cross sections is discussed.

Thermodynamic properties of nonideal plasmas with multiple ionization and Coulomb and hard-core interactions

We present a theoretical approach to the thermodynamic properties of nonideal plasmas consisting of neutral atoms, multiply charged ions, and free electrons. Starting with the free energy, we describe the ionization equilibrium of this system by a coupled set of mass action laws (Saha equations). Our model of interaction takes into account Coulomb forces between all charged particles and hard-core forces between all heavy particles and the electrons. The influence of multiple ionization and different interaction parts on plasma composition, mean charge, and equation of state is discussed for xenon. Finally, we show the potential occurrence of the plasma phase transition.

K-shell ionization induced by 30 MeV/u argon and neon beams

We have studiedK-shell ionization induced by 30 MeV/u Ne and Ar projectiles on target atoms with atomic numbers ranging from 27 to 90. X-ray production cross sections and energy shifts were measured with Si(Li) detectors. In most cases satisfactory agreement between measurements and theoretical direct ionization cross sections is obtained when the contribution of electron capture is included. The influence of multiple ionization on the fluorescence yield ωK is discussed.