Joseph A. Kunc

Collisional-radiative coefficients from a three-level atomic model in nonequilibrium argon plasmas

A three‐level atomic model is used for determining the steady‐state collisional‐radiative coefficients in nonequilibrium partially ionized argon plasmas. Rate equations for populations of the atomic levels are coupled to an electron Boltzmann equation that includes inelastic processes. The solution of these coupled equations yields an analytical form for the non‐Maxwellian electron distribution function. The reabsorption of radiation in the plasma is included through the use of Holstein radiation escape factors [Phys. Rev. 83, 1159 (1951)]. The cross sections in this model are included in the form of simple analytical expressions obtained from a numerical fitting of available experimental data. The results and limitations of the approach are discussed in a broad range of plasma conditions (electron temperature below 25 000 °K and atomic density of 1014–1018 cm−3).

Plasma Parameters Characteristic of Hydrogen Thyratrons under Steady-State Conditions

This paper presents an analysis of the plasma occurring during the steady-state phase in a hydrogen thyratron.

Analytical ionization cross sections for atomic collisions

General analytical expressions for cross sections for direct ionization in atom–atom collisions are evaluated using the classical impulse approximation. The approach is also applied to ion–atom and molecule–molecule interactions. The overall accuracy of the obtained cross sections in a broad range of energy is better, when compared with existing measurements for many collision systems, than accuracy of other analytical predictions available in literature.

Dissociation and ionization of the methane molecule by nonrelativistic electrons including the near threshold region

Several ionization and dissociation channels of electron interaction with the methane molecule are studied using the recently discovered robust scaling law [D. A. Erwin and J. A. Kunc, Phys. Rev. A 72, 052719 (2005)], other experimentally observed relationships between the ionization and dissociation channels, and the most recent information about the processes. The resulting cross sections for the channels are given in the form of analytical expressions valid at all nonrelativistic energies.

Transient energy-release pressure-driven microdevices

A class of transient pressure-driven micromechanical devices that have several advantages over conventional microelectromechanical actuators is described. Although most micromechanical systems developed to date have been involved with electromagnetic or electrostatic forces, in the future micromechanical systems will also involve fluid mechanics, gas dynamics, and thermodynamics at unusually small scales. Generally, the size scaling laws for fluid flows and heat transfer are well understood; however, at the scale of micromachines (say 1-100 mu m), the details of transient behavior become a dominant consideration. The basic principles of transient pressure-driven actuators and some of the factors that must be considered in such designs are discussed. >

An analytical solution of a collisional‐radiative model for nonequilibrium argon plasmas

The general analytical solution of a collisional‐radiative model, including atom–atom inelastic collisions, for nonequilibrium, partially ionized, steady‐state plasmas is presented. This is applied to argon plasmas and the results are compared with previous numerical calculations. The model includes three atomic energy levels; the ground level, one excited level, and continuum, and assumes a Maxwellian electron and atom distribution functions. All rates for collisional and radiative processes are expressed as analytical functions. The model is solved algebraically to obtain analytical expressions for the electron and excited atom densities as a function of the plasma parameters. In the limit of an optically thick plasma the solution agrees with results for complete thermodynamic equilibrium. Solutions are presented for a wide range of conditions (3000≤Te≤24 000 K, 105≤Ne≤NA cm−3, 1014≤NA≤1018 cm−3).

Role of atom–atom inelastic collisions in two‐temperature nonequilibrium plasmas

The contribution of inelastic atom–atom collisions to the production of electrons and excited atoms in two‐temperature (with electron temperature Te, atomic temperature Ta, and atomic density Na), steady‐state, nonequilibrium atomic hydrogen plasma is investigated. The results are valid for plasmas having large amounts of atomic hydrogen as one of the plasma components, so that e–H and H–H inelastic collisions and interaction of these atoms with radiation dominate the production of electrons and excited hydrogen atoms. Densities of electrons and excited atoms are calculated in low‐temperature plasma, with Te and Ta≤8000 K and 1016 cm−3 ≤Na≤1018 cm−3, and with different degrees of the reabsorption of radiation. The results indicate that inelastic atom–atom collisions are important for production of electrons and excited atoms in partially ionized plasmas with medium and high atomic density and temperatures below 8000 K.

Stepwise ionization in a non-equilibrium, steady-state hydrogen plasma

Abstract The paper considers a non-equilibrium, steady-state hydrogen plasma with 10 10 ≲ N e , cm -3 ≲ 10 17 and 8000 ≲ T e , °K ≲ 64,000. The following two cases are analyzed: (1) the plasma is optically thin for all atomic lines and (2) the plasma is optically thick towards the Lyman lines and optically thin for all other lines. Analytical expressions have been obtained for populations and ionization frequencies of excited levels. Populations of the excited levels obtained from the analytical formulas are in good agreement with numerical calculations.

Rate Coefficients for Some Collisional Processes in High-Current Hydrogen Discharges

Rate coefficients are presented for a number of collisional processes important in high-current hydrogen discharges. The energy distribution of the plasma electrons has been assumed to be Maxwellian.

Statistical-mechanical calculations of thermal properties of diatomic gases

The impact of rotational–vibrational dynamics of molecules on the molecular partition functions, law of mass action and thermodynamic functions of partially dissociated diatomic gases is discussed. A group of 11 gases, expected to have their partition functions the most sensitive to the molecular rotational–vibrational properties, is selected for rigorous and detailed studies, and the partition functions, dissociation degrees and free energies of the gases are calculated (using various models of molecular rotational–vibrational dynamics) and compared in a broad range of temperature and particle density.