Electron Impact Ionization Of Ions Research Articles

Experimental method for determination of the integral cross-section for electron impact ionization of ions with optical control of the target’s initial quantum state

A method for measurement of integral cross-sections for electron impact ionization of ions is proposed. The technique involves the application of a quadrupole ion trap with laser-cooled ions. It allows controlling the initial quantum state of the target ions, measuring the cross-sections separately for such states. The methodology is described in detail, together with a discussion of the reliability of optical selection of the ions’ states. The first results for Ca+ ion ionization from 42S1/2 and 32D3/2 states are presented.

Enhancement of electron-impact ionization induced by warm dense environments.

Studies have shown significant discrepancies between the recent experiment [Berg etal., Phys. Rev. Lett. 120, 055002 (2018)PRLTAO10.1103/PhysRevLett.120.055002] and current theoretical calculations on the electron-impact ionization cross section of ions in warm dense magnesium. Here, we present a systematic study the effects of the ionic correlations and free-electron screening on the electron-impact ionization of ions in warm dense matter. The ionic correlation and the free-electron screening effects yield additional Hermitian terms to the calculation of the ionic central-force-field potential, which significantly change the electronic structure compared with that of the isolated ion. In calculating the electron-impact ionization, we describe the impact and ionized electrons using a damped-distorted wave function, which considers the momentum relaxation of free electrons due to collisions with other free electrons and ions. We reproduce the electron-impact ionization process for Mg^{7+} in the solid-density plasma and increase the ionization cross section by one order of magnitude compared with that of the isolated ion, which excellently agrees with the experimental result of Berg etal.

The ion charge-current strength relationship in stationary and pulsed vacuum discharges

It is shown that the electron temperature in the region where the vacuum-discharge plasma is in equilibrium with the intrinsic magnetic field is proportional to the discharge current I and inversely proportional to the coefficient of erosion of the cathode material. For I≥300 A, this region features additional electron-impact ionization of ions coming from the near-cathode layer. As a result, the average ion charge Z increases with the current strength, the Z(I) dependence being more pronounced at a lower discharge pulse duration.

Fundamentals of electron-ion interaction

A brief review on the physics of electron-ion collisions is given. After an introduction focussing on the applied importance of electron-ion interactions a discussion of experimental techniques based on colliding beams of electrons and ions follows. The main part deals with the different types of electron-ion collision processes. An overview is provided on (1) electronimpact ionization of ions, (2) electron scattering from ions, (3) electron-impact excitation of ions, and (4) recombination of ions with free electrons.

Absolute Cross Sections for Single Ionization of Ar+ and Cl+ by Electron Impact

A crossed-beam facility for electron impact ionization of ions was constructed. The absolute cross sections for single ionization of Ar+ and Cl+ ions at electron energies ranging from 30 to 500 eV were measured. The uncertainty is about ±13%.

Energy Distribution of Secondary Electrons in Electron-Impact Ionization of Hydrogen-Like Ions

The energy distribution of secondary electrons in electron-impact ionization of ions is important in computer simulation of high temperature plasmas. Surprisingly enough, no one has published the required data. In this paper, the Coulomb-Born type calculations with and without electron-exchange effect are reported. The 1/ Z 4 scaling law holds fairly well down to smaller Z values, Z being the nuclear charge of the hydrogen-like target ion. The dependence on the incident electron energy is represented fairly accurately by an empirical factor in the approximation without electron exchange.

Electron-Impact Ionization Data for the Nickel Isonuclear Sequence

Atomic data for the electron impact ionization of ions in the nickel isonuclear sequence are reviewed. Calculations have been performed for all charge states in the distorted-wave approximation. In 8 of the 28 ions of the nickel isonuclear sequence, experiment and theory are compared. In many of the ions, excitation-autoionization contributions to the total cross section are found to be quite important. For intermediate charge state ions a large fraction of the experimental cross section may be attributed to ionization from metastable levels of low-lying excited configurations. Maxwellian collisional rate coefficients are calculated from the cross section data and presented in parametrized form.

HIGH-RESOLUTION MEASUREMENTS OF ELECTRON-IMPACT IONIZATION CROSS SECTIONS FOR LI-LIKE IONS

For crossed electron and ion beams we have developed an experimental technique which allows to measure cross sections for electron impact ionization of ions with relative uncertainties less than 0.1 %. At this level of accuracy it is possible to do ion spectroscopy of intermediate excited states contributing to net ionization via single and multiple autoionization processes. For ions B2+, C3+, N4+ and O5+ along the Li isoelectronic sequence we have performed quantitative measurements of state-resolved contributions from excitation-autoionization (EA), resonant-excitation-double autoionization (REDA) and resonant-excitation auto-double-ionization (READI).

Resonances in electron-impact single, double, and triple ionization of heavy metal ions.

We report narrow dielectronic capture resonances decaying by double autoionization observed for the first time in electron-impact ionization of ions. We also observe corresponding peaks in double and triple ionization leading us to postulate new processes where dielectronic capture is followed by triple or quadruple autoionization, respectively.

Polarization and angular correlations in electron-ion collisions

Studies of polarization and angular correlations in electron-ion collisions can reveal a wealth of information about the collision dynamics. Three different processes are considered as an application of the electron-atom problem: Electron-ion scatterings; electron-impact ionization of ions; and radiations from residual ions. The polarization and angular correlations are presented in concise parametrized expressions in terms of known functions of angles. Angle-independent dynamic parameters in the expressions provide a convenient classification of dynamic effects and facilitate comparison between theory and experiment.

Electron impact ionization data for the iron isonuclear sequence

Atomic data for the electron impact ionization of ions in the iron isonuclear sequence are reviewed. The best available data are identified. Comments are made on current research activities leading to future data for iron ions.

An improved crossed-beams technique for the measurement of absolute cross sections for electron impact ionisations of ions and its application to Ar+ions

Based on the animated-beam method of Brouillard and co-workers (1983) an improved experimental technique has been developed to measure cross sections for electron impact ionisation of ions. In a crossed-beams arrangement the overlap of the electron and the ion beam is periodically varied by a mechanical displacement of the complete electron gun system. Simultaneously with the ionisation signal, the parent ion beam current and the velocity of the gun movement are registered. As a test of the new method cross sections for single ionisation of Ar+ ions are measured from threshold up to 850 eV electron energy. The results are in excellent agreement with the crossed-beams data of Woodruff et al.

A new technique for the measurement of ionization cross sections with crossed electron and ion beams

A new experimental technique has been developed and used to measure cross sections for electron impact ionization of ions. Each single cross section is determined independently absolute by moving the electron gun mechanically across the ion beam with simultaneous registration of the ionization signal and the actual beam current. Different from the method of Brouillard et al. it is not necessary then to provide constant speed of the motion. Typical relative uncertainties of the measured cross sections are of the order of ±2% and absolute total errors are usually within ±6.5%. Very good agreement of ionization cross sections σ 1,2 measured with our new technique for Ar + ions is found with data from Harrison's group. Cross sections for single and multiple ionization of singly and multiply charged ions of Ar, Kr, Sb and Bi have been measured from threshold to 1000 eV.

Electron Impact Ionization of Multicharged Ions

The available literature on electron impact ionization of ions of charge + 3 or greater is reviewed. Several easily used formulae are presented-the classical result, the Lotz formula, and a scaled Coulomb-Born prescription. The available experimental cross-sections, which now include a few good quality crossed-beams measurements, are compared with the cross-sections obtained from the formulae and, where available, with true Coulomb-Born calculations. The Lotz formula is overall found to be closest to the experimental results. However, this result is fortuitous since much of the experimental data are found to contain measurable contribution from the excitation-autoionization process not included in any of the formulae. It appears to be more important to include estimates of the excitation-autoionization contribution to ionization cross-sections than to improve the models of the direct ionization process.

The Advantages of Combining an EBIS with the PIGMI Technology

The Electron Beam Ion Source (EBIS) produces highly charged heavy ions by electron impact ionization of ions electrostatically trapped within a dense energetic electron beam. Because of its pulsed operation and the highly charged ions produced, the EBIS is ideally suited as an injector for a high-gradient, low duty-cycle linac such as that being developed at the Los Alamos Scientific Laboratory (LASL) in the program to design a Pion Generator for Medical Irradiation (PIGMI). This combination of new technologies would produce an efficient, small heavy ion linac useful in a variety of research and practical applications.

Electron impact ionization of argon ions by trapped ion cyclotron resonance spectroscopy

Trapped ion cyclotron resonance spectroscopy has been used for the first time to study the electron impact ionization of ions. Production of Ar 2+ has an appearance potential of about 17 ± 0.5 eV arising from ionization of Ar +, while production of Ar 3+ has a value of approximately 30 ± 0.5 eV arising from ionization of Ar 2+. The formation of metastable ion intermediates is postulated to explain the results.