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ABSTRACT: A study has been performed on the emissive characteristics of a cold graphite cathode in a magnetically insulated coaxial diode under the action of nanosecond accelerating pulses at a pulse repetition frequency (PRF) of up to 3.5 kHz. Emission was observed to degrade at PRF < 1 kHz and recover at PRF ~3.5 kHz. Estimates of the temperature conditions in the region of an explosive electron emission (EEE) center have shown that the pulse interval t~1 ms suffices for this region to cool down to 300 K. The cooling occurs predominantly by heat conduction. For t~0.3 ms, the residual heat is substantial. It has been proposed that there exists a frequency limit for the cathode microrelief polishing effect. The results of an experiment on the study of the mechanism of cathode emission recovery with increasing PRF are presented. Micrographs of the cathode taken after aging, photographs of the cathode in operation, and analyses of the fractional composition of the material removed from the cathode suggest that heating of some regions of the cathode emitting edge to the melting point of graphite plays an important role in the recovery of emission. This counts in favor of the hypothesized dominant contribution of thermoelectronic emission to the initiation of EEE due to the residual heat remaining in regions that have not cooled off during the pulse interval
IEEE Transactions on Plasma Science 10/2006; 34(5):1771 - 1776. · 1.17 Impact Factor
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ABSTRACT: The prebreakdown and initial stages of discharge in high-pressure gas filled gaps under the action of subnanosecond high-voltage
pulses have been experimentally and theoretically studied. The breakdown appears as a bright flash almost homogeneously filling
the interelectrode gap within a period of time on the order of 100 ps. The observed phenomena are theoretically interpreted
using a model that takes into account the heating of electrons due to collisions with gas molecules and the electron-impact
ionization of these molecules. Calculations show that gas ionization is performed by “hot” electrons and has either a step-or
flashlike character, in agreement with experimental observations. The characteristic time of ionization is 10–20 ps. The results
lead to the conclusion that, using high-pressure gas discharge switches, it is possible to obtain voltage pulses with front
widths on the order of several dozen picoseconds.
Technical Physics Letters 01/2006; 32(9):745-749. · 0.56 Impact Factor
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ABSTRACT: We have studied the electron emission from graphite cathodes under the action of voltage pulses with an amplitude of up to
300 kV, a pulse duration of 10−9 s, and a pulse repetition frequency of 1–3.5 kHz. The magnetically insulated electron beam had a peak power of up to 600
MW at an average power of 1–3 kW. The dynamics of emission current delay was studied in relation to the charge transferred
by the beam and to the state of the cathode surface (studied by scanning electron microscopy). It is established that smoothening
of the microrelief leads to degradation of the cathode emissivity, which can be compensated by increasing the pulse repetition
rate above a certain critical level.
Technical Physics Letters 09/2004; 30(10):813-816. · 0.56 Impact Factor
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ABSTRACT: The processes of origin of centers of explosive emission are considered at operation of a cathode spot of a vacuum arc. It was supposed, that the origin of centers is stipulated by absorption by a cathode surface of a variable electromagnetic field energy. It was supposed also, that such field takes place in a layer separating discharge plasma from the cathode. Some versions are considered, when the material of the cathode has no dispersion properties, can exhibit properties of a dispersion, and also case of absorption of electromagnetic waves by microparticles, flying from the cathode.
Discharges and Electrical Insulation in Vacuum, 2002. 20th International Symposium on; 02/2002
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ABSTRACT: The electrohydrodynamic and thermal instability development on a conducting liquid surface exposed to a strong electric field
was studied by methods of two-dimensional numerical modeling. The Navier-Stokes equation was solved and the surface cone heating
by the field emission current was described. It is demonstrated that the free surface evolution in this system leads to an
avalanche-like growth in the cone tip temperature and the resulting explosion-like field electron emission. A considerable
contribution to the liquid heating is due to a surface energy source (the Nottingham effect). The proposed computational method,
based on the domain transformation to a canonical form, can be used to develop dynamic models of the liquid-metal ion source
operation and to analyze the interaction of a gas plasma with a liquid metal surface in the cathode spot of a vacuum arc.
Technical Physics Letters 01/2001; 27(5):370-372. · 0.56 Impact Factor
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ABSTRACT: In the report the possible gears of explosion emission center initiation in cathode spot of vacuum arc under operation of electromagnetic radiation flow from plasma and brought from an external power source are considered (we call natural such radiation). The given radiation, acting with boundary layers to cathode surface with different values of complex conductivity, can provide conditions of a repetition of operation of cathode spot
Discharges and Electrical Insulation in Vacuum, 2000. Proceedings. ISDEIV. XIXth International Symposium on; 02/2000
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ABSTRACT: 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
Discharges and Electrical Insulation in Vacuum, 2000. Proceedings. ISDEIV. XIXth International Symposium on; 02/2000
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ABSTRACT: 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, with the angle of the cone depending on the initial shape of the surface. We describe this structure as a dynamic Taylor cone. The time-dependent profiles of the surface shape are 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 run-away 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 overtakes the growth of both the surface tension and viscous stress acting inwards. Analysis of the time dependences of physical values can strongly assist the development of analytical treatments of such phenomena, and give insight into the problem of the dynamic description of operating liquid metal ion source atomisers. 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 the evolution of the surface occurs in the context of a Langmuir shield.
J. Phys. D: Appl. Phys. 01/2000; 33:1245-1251.
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ABSTRACT: The paper presents results of non-stationary 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 mainly flows through the edges of the emission center. A
mechanism for the motion of a cathode spot has been proposed
IEEE Transactions on Dielectrics and Electrical Insulation 09/1999; · 1.09 Impact Factor
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ABSTRACT: The influence of the finite velocity of energy relaxation of
nonequilibrium holes on the heat instability development leading to a
vacuum breakdown has 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 Nottingham's effect and the vacant states induced by the emission
process leads to the effectiveness of the Nottingham heating decreasing
at the early stages of a cathode initiation of a vacuum breakdown
IEEE Transactions on Dielectrics and Electrical Insulation 09/1999; · 1.09 Impact Factor
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ABSTRACT: 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 (⩽3500 K),
field strengths (⩽1.5×10<sup>8</sup> 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</sup> A/cm<sup>2</sup>)
IEEE Transactions on Dielectrics and Electrical Insulation 09/1999; · 1.09 Impact Factor
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ABSTRACT: 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 Grad's 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 (⩽3500 K), field strengths
(⩽1.5.10<sup>8</sup> V cm<sup>-1</sup>) and work function (3.0-4.5
eV) of the emitter. A considerable deviation from the Fowler-Nordheim's
theory results was found for high current density (>10<sup>9</sup>
A/cm<sup>2</sup>)
Discharges and Electrical Insulation in Vacuum, 1998. Proceedings ISDEIV. XVIIIth International Symposium on; 09/1998
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ABSTRACT: 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
Discharges and Electrical Insulation in Vacuum, 1998. Proceedings ISDEIV. XVIIIth International Symposium on; 09/1998
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ABSTRACT: The obtained value of velocity potential (φ) within the range
4⩽φ⩽6 corresponds to the microstream development and the
following explosion which can be calculated exactly for the moment of
the explosion, and can be measured experimentally as well in the
development of a cathode spot in vacuum arcs. Experimental values of
φ for different metals are within the range 4-6 V which corresponds
to the authors' results. As appears, from the estimates received and the
following estimates, inertness of the liquid in certain local regions is
not an obstacle for superfast hydrodynamic processes. Corresponding
hydrodynamic disturbances will lead to an appearance of one or several
special protuberances on the film. At heavy unevenness on the film, the
theory given above loses its power (it is obvious from the comparison of
times) and it is necessary in this case to research a new model of the
process
Discharges and Electrical Insulation in Vacuum, 1998. Proceedings ISDEIV. XVIIIth International Symposium on; 09/1998
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[show abstract]
[hide abstract]
ABSTRACT: 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 Nottingham's effect and the vacant states induced by the emission
process lead to the effectiveness decreasing of the Nottingham's heating
at the early stages of a cathode initiation of a vacuum breakdown
Discharges and Electrical Insulation in Vacuum, 1998. Proceedings ISDEIV. XVIIIth International Symposium on; 09/1998
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ABSTRACT: The paper presents a two-dimensional hydrodynamic model of a
high-current vacuum arc. The main areas of interest of this numerical
modeling are arc column and anode areas. Homogeneous current density and
ion flows from the cathode region are assumed. The results of numerical
calculations of current and ions flow to the anode in dependence of
discharge gap and total current are given and a possible scenario for
the transition from the diffuse to the anode-spot mode is
discussed
Discharges and Electrical Insulation in Vacuum, 1998. Proceedings ISDEIV. XVIIIth International Symposium on; 09/1998
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ABSTRACT: 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
IEEE Transactions on Plasma Science 07/1998; · 1.17 Impact Factor
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ABSTRACT: The problem of the motion of the cathode spot of a vacuum arc electrical discharge in a magnetic field applied tangential
to the cathode surface is considered. The treatment is based on concepts of the nonstationary, cyclical nature of processes
occurring in the cathode spot and the key role of return electrons falling out of the near-cathode plasma back onto the cathode.
Technical Physics 05/1998; 43(6):668-672. · 0.50 Impact Factor
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ABSTRACT: 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. The processes of energy release and dissipation in the bulk of a
metallic thermal field-emission cathode have been investigated in the
approximation of two-fluid hydrodynamics for electrons and phonons
IEEE Transactions on Dielectrics and Electrical Insulation 01/1998; · 1.09 Impact Factor
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ABSTRACT: The paper presents a two dimensional (2-D) hydrodynamic model of
vacuum arc emission center-“ecton”-which is an outgrowth of
the one-dimensional problem that we have solved earlier. The numerical
simulation was carried out for the initial stage of the operation of the
cathode spot of a low-current vacuum arc on a copper cathode. It has
been shown that, in terms of this model, the current flows in the main
through the edges of the cathode spot. Based on a these data, a
mechanism for the motion of a cathode spot has been proposed
IEEE Transactions on Plasma Science 09/1997; · 1.17 Impact Factor
