Anode spot vacuum arc model: graphite anode

Abstract

A model of near anode processes in vacuum arc anode spots on graphite electrode is developed. The physical model is based on a kinetic treatment of anode evaporation and plasma production. The system of equations formulated in the paper includes description of plasma flow in the kinetic and in the plasma acceleration regions in a self-consistent manner. Spot parameters, such as, anode surface temperature, current density, plasma density and temperature, plasma velocity in the near-electrode region and in region of plasma expansion are calculated numerically. The calculation includes the dependence of spot parameters on anode erosion rate, initial anode surface temperature and spot life time. The calculations indicate that Joule energy in the anode body is significant, and in some cases may exceed the anode surface energy source (difference between the electron energy flux and energy flux related to the anode mass loss). The anode erosion rate in vacuum arc can sufficiently differ from the anode material evaporation rate in vacuum obtained by Dushman formula.Index Terms-Anode plasma, anode spot, current density, erosion rate, graphite, plasma density and degree of atom ionization, vacuum arc.

Arc plasma synthesis of carbon nanostructures: where is the frontier?

“…Exceptions are the few works in which cathodic arc was used [39]. Anodic arc is characterized by primary anode ablation during the arc process in contrast to cathodic arc in which cathode ablation prevails [40]. When the anodic arc is implemented for CNT synthesis it is supported by the ablation of the anode material and a substantial part of the ablated material (about 70%) is deposited on the cathode.…”

Modeling of a Microscale Short Vacuum Arc for a Space Propulsion Thruster

“…The plasma is produced by atom ionization of the electrode material. The kinetic models developed for cathode [7] and anode [23] spots were used. According to the kinetic model, the ionized electrode vapor structure consists of the several partially overlapping regions, which included a ballistic zone comprising a space charge sheath at the surface, a nonequilibrium plasma kinetic layer, and an electron emission relaxation zone.…”

“…The mathematical model also includes the equations of electron emission in general form, and for total spot current, electric field at the electrode surface, kinetics of direct and back heavy particle fluxes, fluxes of the charged particles to the electrodes, electrode energy balances, and plasma energy balance [7], [10], [23]. The calculated parameters are the electron temperature T e , anode potential drop U an , heavy particle density n, degree of ionization α, cathode T c and anode T a temperatures and erosion rate G, electric field E, total current density j and ion current density j i in the cathode spot, plasma plume velocity V for a given U c and I, and anode spot radius r a .…”

Mechanism of carbon nanostructure synthesis in arc plasma

“…28 Anodic arc is characterized by primary anode ablation during the arc process in contrast to cathodic arc in which cathode ablation prevails. 29 When anodic arc is implemented for carbon nanotube synthesis it is supported by ablation of the anode material and substantial part of the ablated material ͑about 70%͒ is deposited on the cathode. Two different textures and morphologies can be observed in the cathode deposit; the gray outer shell and darksoft inner core deposit.…”