E. E. Kunhardt

Generation of large-volume, atmospheric-pressure, nonequilibrium plasmas

A review is presented of the issues associated with the generation of large-volume, high-pressure, nonequilibrium plasmas, as well as the approaches that have been developed for generating these plasmas using electrical discharges in gases. The various instabilities that have been overcome to obtained these plasmas as well as the techniques for quenching them are also reviewed. Last, recent efforts to obtain atmospheric pressure plasmas are discussed with particular emphasis on the capillary plasma electrode discharge, which we have used to obtain high (electron) density nonequilibrium plasmas.

Development of pulsed dielectric breakdown in liquids

A model is presented for the development of breakdown in liquids subjected to uniform high amplitude electric field stresses with duration of microseconds or less. In this model, breakdown proceeds in four stages: (i) formation of a low density site (nucleation) in the liquid near an electrode, (ii) growth and expansion of this site until the local density is reduced below a critical density for electron impact ionization to take place, (iii) growth of an electron avalanche and its transformation into an ionizing front, and (iv) propagation of the ionization front via a sequence of processes occurring in the region ahead of the front; namely, heating by electron injection, lowering of the liquid density and avalanche growth and retardation. Expressions for the duration of each of these stages are derived and their behaviour with pressure and field strength analysed for cathode initiated breakdown. From this, a critical energy criterion for breakdown is obtained. Comparison is made with experimental results for water, salt solutions, and the liquid noble gases and for pulse durations in the microsecond and sub-microsecond time scales. This model serves to elucidate the dynamics of pulsed breakdown of liquids.

The liquid state and its electrical properties

Theories of Liquid Structure.- Field Theoretic Models of Liquids.- The Structure of Simple Fluids.- Dynamic Processes in Liquids and Selected Topics Related to the Dynamics of Ions and Electrons in Liquids.- Ionic and Electronic Processes.- Theories of Electrolyte Solutions.- Theoretical Studies of Electrons in Fluids.- Geometrical Perspectives of a Solvated Electron.- Electron Localization and Femtosecond Nonlinear Optical Responses in Liquids.- Strong Field Effects and Molecular Dynamics Simulations.- Electron Kinetics in Nonpolar Liquids - Energy and Pressure Effects.- Photoconductivity, Conduction Electron Energies, and Excitons in Simple Fluids.- Electron Scattering and Mobility in Dielectric Liquids.- Hot Electron Mobility and Electron Attachment in Non-Polar Liquids.- Gas/Liquid Transition: Interphase Physics.- Calculations of Vo and the Energy Dispersion of Electrons in Rare Gas Liquids.- Interfacial Phenomena.- Electrical Aspects of Liquid/Vapor, Liquid/Liquid, and Liquid/Metal Interfaces.- Space Charge Effects in Dielectric Liquids..- Breakdown and Conduction.- An Overview of Electrical Processes Leading to Dielectric Breakdown of Liquids.- Electron Scattering and Dielectric Breakdown in Liquid and Solid Dielectrics.- Streamers in Liquids.- Electric Conduction in Dielectric Liquids.- Measurement of Electrical Breakdown in Liquids.- Appendices.- Appendix A: Abstracts of Poster Papers.- Appendix B: Organizing Committee.- Appendix C: Lecturers.- Appendix D: Participants.

Energy balance in a nonequilibrium weakly ionized nitrogen discharge

The time evolution of the energy balance in a nitrogen discharge during its early phases of development is simulated using a self‐consistent calculation of the electron distribution function (EDF), the vibrational population (VP), and densities of some electronically excited states. The contribution of the V–T (vibration‐to‐translation), and V–V (vibration‐to‐vibration) energy exchanges is quantitatively analyzed. The contribution to the energy balance by self‐quenching reactions of the N2(A3Σ+u) state is also analyzed. It is shown that the population of this state in a discharge and its contribution to the energy balance may be significant.

Towards a more accurate flux corrected transport algorithm

Abstract An algorithm is discussed for solving first-order hyperbolic equations whose solution may exhibit very steep and changing gradients (shock-like) and large dynamic range. In developing the algorithm, emphasis has been placed on obtaining more accurate solutions. The algorithm is based on Flux Corrected Transport techniques.

Monte Carlo technique for simulating the evolution of an assembly of particles increasing in number

Abstract We describe an algorithm for simulating the evolution of an assembly of particles which is increasing in number. It is based on the use of the Monte Carlo method and a renormalization procedure which allows the mapping of the growing assembly into another consisting of fewer particles. The results of test calculations are presented and error analysis of the results are included.

Direct solution of Poisson's equation in cylindrically symmetric geometry: A fast algorithm

Abstract We describe a new algorithm for directly solving Poissons equation in cylindrically symmetric geometries. It is based on the use of fast Fourier transforms for the axial solution, and a novel expansion in cubic splines for the radial solution. Error and stability analyses of the algorithm are included, and the results of test calculations are presented. The algorithm has proved stable, reasonably fast, and able to handle very stiff driving functions.

Pre‐breakdown currents in water and aqueous solutions and their influence on pulsed dielectric breakdown

The current response of water and sodium chloride solutions subjected to high amplitude electric fields of sub‐microsecond duration has been investigated. The prebreakdown current‐voltage relationship for these liquids is found to be nearly linear for the fields considered and therefore described by a resistance, R. For constant concentration, R does not extrapolate to zero as the gap width, d, goes to zero, suggesting the presence of a high resistivity sheath near the electrodes. Estimates for the sheath parameters (electric field in the sheath, Es, width, dl, formation time, tl, and ion density, ns) are obtained from these measurements. The contribution of electronic and ionic currents to the breakdown probability has been assessed from the power input to the liquid during the pre‐breakdown phase. For applied fields with sub‐microsecond duration, the input power is primarily due to electron field emission currents whose magnitude is a function of the field in the ionic sheath. For the parameters investi...

Kinetics of hydrogen thyratron plasmas during the conduction phase

A study of the conduction‐phase characteristics of hydrogen thyratron plasmas is presented. A self‐consistent analysis is performed through simultaneous numerical solutions of the Boltzmann equation, the rate equations for the various ionic and neutral particle densities, and the radiative transfer equation. The electron kinetic properties, chemical composition, and radiative properties of the plasma are derived for a wide range of current densities. Moreover, the role of the various collisional processes in shaping the electron energy distribution for various values of E/N (electric field/total gas number density), fractional ionization, and dissociation degree is elucidated. Implications of the obtained plasma properties on the analysis and diagnosis of hydrogen thyratron plasmas are discussed.

Gas heating effects in hydrogen thyratron discharges

A theoretical study of the effects of gas heating in hydrogen thyratron discharges is presented. Coulomb collisions between electrons and ions are identified to contribute predominantly to gas heating. Time‐dependent numerical solutions for the gas temperature, as well as the electron and chemical kinetics are obtained. It is shown that the electron temperature can be significantly higher than that calculated using a cold gas assumption. A mechanism is proposed by which quenching can occur due to the onset of a gas temperature maximum for which the required current during the conduction phase cannot be maintained in the grid aperture region. The time it takes for the gas temperature to reach the quenching point is presented as a function of the current density.