E.A. Litvinov

The computer simulation of the vacuum arc emission center

The paper presents a two-dimensional hydrodynamic model of vacuum arc emission center-ecton, which is an outgrowth of the one-dimensional problem that they have solved in their earlier papers. Also given are refined equations of state for matter in a transitory phase.

Computer simulation of ecton in vacuum arc

The paper presents results of nonstationary two-dimensional hydrodynamic model of vacuum arc emission center-ecton. The numerical simulation was carried out for the initial stage of the operation of the ecton of a low-current vacuum arc on a copper cathode. It was shown that the current flows in the main through the edges of the emission center. A mechanism for the motion of a cathode spot has been proposed.

Initiation of explosive electron emission in microwave fields

The microwave breakdown has been studied for the case in which it is caused by the heating and subsequent thermal destruction of the micropoints present on the cathode surface subjected to the action of a rapidly varying electric field. The heating of a micropoint by the emission current induced by a microwave field has been numerically simulated using the two-temperature model. The delay time to breakdown has been calculated as a function of the frequency of the electric field oscillation for different micropoint geometries.

A self-consistent model of electron emission from metals

We present a model of electron emission from metals, which takes into account deviation of the electron distribution function from the Fermi equilibrium form inside the cathode under the emission effect. Using the Grad method electron distribution function, the emission boundary is expressed consecutively in terms of its hydrodynamic moments: temperature, average velocity, heat flux density. These hydrodynamic moments are caused by the emission itself and thus need a self-consistent determination. New easy-to-use equations for the emission current density, emission heat flux, and total energy distribution function of the emitted electrons are proposed. Consideration was made for a wide range of temperatures (/spl les/3500 K), field strengths (/spl les/1.5/spl times/10/sup 8/ V/cm) and work function (3.0 to 4.5 eV) of the emitter. A considerable deviation from the Fowler-Nordheim (FN) theory was found at high current density (>10/sup 9/ A/cm/sup 2/).

Time-dependent modelling of electrohydrodynamic effects on the surface of a liquid metal

Results of time-dependent modelling of electrohydrodynamic effects on the surface of a liquid metallic conductor are reported for a regime where no electron, ion or particle emission occurs. The Navier-Stokes equations, with free liquid boundaries subject to Maxwell field stress, surface-tension stress and viscous action, have been solved by a method that uses transformation of the interfaces into a rectangle; this overcomes a problem of surface oscillations that appeared using the Marker-and-Cell technique. The situation geometry is a deep unbounded surface with axial symmetry. With time, an almost flat surface evolves into a cone-like shape, which is in good agreement with experimental observations of this process. The calculations have also shown that, when the protrusion is formed, the time dependences of the surface radius of curvature, the electric field value at the protrusion apex, and the axial velocity of the liquid metal, exhibit a runaway behaviour: the physical values become very large for a short time. As a cusp evolves on a surface, the Maxwell stress acting outwards becomes very large and overtake the growth of both the surface tension and viscous stress acting inwards. The development of numerical methods using transformation of the interfaces appears very useful for the treatment of problems in which the cathode or the anode significantly change shape. This situation occurs, for example, when a liquid surface is covered by a metal plasma and evolution of the surface occurs in the context of a Langmuir shield.

Nonequilibrium phenomena accompanying high-current thermal field emission

The paper presents the results of a theoretical analysis of the influence of electric fields, temperature gradients and the effects of mutual electron-phonon drag on the thermal-field-emission properties of metals. In approximation of two-fluid hydrodynamics for electrons and phonons, the processes of energy release and dissipation in the bulk of a metallic thermal-field-emission cathode have been investigated.

Recycling of centers of explosive emission in a cathode spot of a vacuum arc

Analyze non-stationary processes on the cathode and in near cathode of area of a vacuum arch. Such processes can result in periodicity of occurrence of the centers of explosive emission in cathode spot.

Kinetic theory approach for energy exchange processes in high-current electron emission

The influence of the finite velocity of energy relaxation of nonequilibrium holes on the heat instability development leading to a vacuum breakdown have been investigated. For this purpose, a new more complete self-consistent approach has been proposed and developed which allows a description of field electron emission and energy exchange processes in high-current electron emission. It has been shown that taking into account the spatial distribution of the energy dissipation due to Nottinghams effect and the vacant states induced by the emission process lead to the effectiveness decreasing of the Nottinghams heating at the early stages of a cathode initiation of a vacuum breakdown.

A self-consistent model of electron emission from metals at high current density

The authors present a model of electron emission from metals, which takes into account deviation of the electron distribution function from the Fermi equilibrium form inside the cathode under the emission effect. Using Grads method, the electron distribution function at the emission boundary is expressed consecutively in terms of its hydrodynamic moments (temperature, average velocity, heat flux density). As these hydrodynamic moments are caused by the emission itself and depend upon distribution function at the emission boundary, they need self-consistent determination. New easy-to-use formulae for the emission current density, emission heat flux and total energy distribution function of the emitted electrons are proposed. Consideration was made for a wide range of temperatures (/spl les/3500 K), field strengths (/spl les/1.5.10/sup 8/ V cm/sup -1/) and work function (3.0-4.5 eV) of the emitter. A considerable deviation from the Fowler-Nordheims theory results was found for high current density (>10/sup 9/ A/cm/sup 2/).

Thin superconducting films at field emission

An analysis of the kinetics of the electron subsystem of a superconductor based on a model with a phonon thermostat has shown that the nonequilibrium state of a superconducting thin- film cathode that appears at field emission changes the superconducting properties of the cathode as compared to the equilibrium state. The dependence of the superconducting gap on the intensity of the emissive source has been obtained.