Constantine E. Theodosiou

Quantum defect values for positive atomic ions

Abstract The asymptotic quantum defects, at the ionization limit, of s, p, d, and f atomic orbitals have been calculated in the Hartree-Slater approximation for all ionization stages of all ions with atomic number Z ⩽ 50.

Revisiting the anomalous RF field penetration into a warm plasma

Radio frequency (RF) waves do not penetrate into a plasma and are damped within it. The electric field of the wave and plasma current are concentrated near the plasma boundary in a skin layer. Electrons can transport the plasma current away from the skin layer due to their thermal motion. As a result, the width of the skin layer increases when electron thermal velocity is taken into account. This phenomenon is called the anomalous skin effect. The anomalous penetration of the RF electromagnetic field occurs not only for the electric field parallel to the plasma boundary (inductively coupled plasmas), but also for the electric field normal to the plasma boundary (capacitively coupled plasmas). Such anomalous penetration of the RF field modifies the structure of the RF sheath in capacitive coupled plasma. Recent advances in the nonlinear, nonlocal theory of the capacitive sheath are reported. It is shown that separating the electric field profile into exponential and nonexponential parts yields an efficient qualitative and quantitative description of the anomalous RF field penetration in both inductively and capacitively coupled plasmas

Transition probabilities for the helium singly excited states 1snl 1,3L with n = 2–21 and l = 0–5

Theoretical dipole transition probabilities, oscillator strengths, lifetimes, and branching ratios are presented for all transitions between states of the He 1snl series with nless than or equal to21 for singlet and less than or equal to22 for triplet states, and lless than or equal to5. The experimental wavelengths are also tabulated. The calculations were performed by a recently developed approach which combines the traditional Coulomb approximation with the representation of the atomic core by a realistic central-field potential. copyright 1987 Academic Press, Inc.

Enhanced collisionless heating in a nonuniform plasma at the bounce resonance condition

The importance of accounting for a nonuniform density profile for modeling of collisionless electron heating in a bounded low-pressure plasma is demonstrated. A drastic enhancement of the power transfer into an inductive plasma under the condition of a bounce resonance is observed if the nonuniformity of the plasma density profile is accounted for. This enhanced plasma heating is attributed to the increase of the number of resonant electrons, for which the bounce frequency of electrons confined inside the plasma potential is equal to the rf field frequency.

Landau damping and anomalous skin effect in low-pressure gas discharges: Self-consistent treatment of collisionless heating

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for t...

Self-consistent modeling of nonlocal inductively coupled plasmas

In low-pressure radio-frequency (RF) discharges, the electron-energy distribution function (EEDF) is typically non-Maxwellian for low plasma density. The nonlocal plasma conductivity, plasma density profiles, and EEDF are all nonlinear and nonlocally coupled. For accurate calculation of the discharge characteristics, the EEDF needs to be computed self-consistently. The method of fast self-consistent one-dimensional of planar inductively coupled discharges driven by a RF electromagnetic field is presented. The effects of a non-Maxwellian EEDF, plasma nonuniformity, and finite size, as well as the influence of the external magnetic field on the plasma properties are considered and discussed

Landau Damping and Anomalous Skin Effect in Low-pressure Gas Discharges: Self-consistent Treatment of Collisionless Heating

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for the nonuniform plasma density profile for computing the current density profile and the EEDF is demonstrated. The enhancement of collisionless heating due to the bounce resonance between the electron motion in the potential well and the external radio-frequency electric field is investigated. It is shown that a nonlinear and self-consistent treatment is necessary for the correct description of collisionless heating.

Three-dimensional Monte Carlo/particle-in-cell Simulations of the discharge pulse in an AC-PDP cell

The dynamics of the discharge pulse between coplanar electrodes in an alternating current plasma display panel (ac-PDP) cell is studied by the three-dimensional (3-D) Monte Carlo/particle-in-cell (PIC) simulations. The images obtained from the simulations capture all essential features of the discharge (such as a spatial structure of striations above the anode, and an arch-shaped front of the discharge spreading along the cathode) and show a remarkable resemblance to the experimental data.

Lifetimes of singly excited states in Cu + and Ag +

The lifetimes of all the known singly excited states in Cu+ and Ag+ were calculated by using a realistic potential (Hartree–Slater) to represent the atomic (ionic) core. Since ab initio calculation of transition wavelengths still lags greatly behind experiment, we used the available experimental values. The results obtained are in good agreement with available sparse experimental data of lifetimes and are intended for guidance of future experimental investigations. The present numerical Coulomb-approximation approach is free from artificial integration cutoffs employed in the various widely used Coulomb approximations.

Lifetimes of the Singly Excited States in Li II

Rydberg state lifetimes in the singly ionized lithium atom were calculated using an inward integration approach and a Hartree-Slater potential to represent the ionic core. The calculated oscillator strengths for the s-p and p-d transitions compare favorably with high accuracy calculations using Hylleraas-type wavefunctions for the limited number of states for which such results are available. Comparison with the also sparse experimental studies of lifetimes is good overall and our predictions indicate specific revisions of some experimental determinations. The effects due to black-body radiation were explicitly included, but found to be insignificant for the states with n < 11, even at temperatures of 600 K.