A new model for the replacement process in electron emission at high fields and temperatures

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.

Initiation of explosive electron emission in microwave fields

Que ce soit dans l‟etude du claquage sous vide ou dans les sources d‟electrons par effet de champ, l‟emission electronique est un phenomene physique essentiel qui a lieu et devient dominante a la cathode sous haute tension. Dans le cas du claquage sous vide, la premiere etape de ce mecanisme est l‟emission d‟electrons au sommet de rugosites presentes sur la surface. Celles-ci peuvent etre representees sous la forme de pointes. Dans le cas des sources d‟electrons, l‟emission des electrons peut se faire au niveau d‟emetteurs qui eux aussi peuvent etre decrits sous la forme de « pointes » distribues de maniere ordonnee sur la surface. Un modele numerique decrivant l‟emission thermo-ionique assistee par effet de champ a ete developpe dans le cas d‟une pointe axisymetrique et dont le traitement peut etre reduit en 2D.Il s‟agit la d‟un probleme multi-physique couple necessitant la resolution de problemes de differentes natures : quantiques, electrostatique, electrocinetique et thermique. A partir de ce modele, l‟etude de l‟emission et du claquage au sommet d‟une pointe soumise a une pulse electrique de l‟ordre de la nanoseconde a ete etudiee. L‟etude de l‟emission electronique sur une cathode soumise a la haute tension et illumine par un laser picoseconde a ensuite ete faite en developpant un modele qui decrit notamment le chauffage du metal en regime hors equilibre. Enfin, dans le cas du claquage sous vide, la modelisation de l‟interaction entre des microparticules, presente dans l‟espace inter-electrodes,et de l‟emission electronique provenant du sommet d‟une rugosite a ete realisee. Differents regimes de trajectoires de la microparticules ont ete observee suivant le courant applique au sommet de la rugosite.

https://tel.archives-ouvertes.fr/tel-01709866/document

Modélisation des phénomènes physiques intervenant au cours de l’émission électronique sous haute tension sous vide

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/).

A self-consistent model of electron emission from metals

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 (/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-Nordheim's theory results was found for high current density (>10/sup 9/ A/cm/sup 2/).

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

Nonequilibrium effects in high current field emission

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Nonequilibrium effects in high current field emission