Once again about a cathode spot of the vacuum arc

Abstract

The movement of electrons in the neighborhood of a cathode spat cell is considered. The cell current is a pulse with a rising-up part and a descending part of about 5.10-9s time duration each. This current generates the magnetic field around the cell. During these rising-up and descending current stages, electric fields with an amplitude up to 3.5.107 V/cm are induced in the neighborhood of the cell. Thus, around the cell, near the cathode surface, the crossed fields E x B are building up which amplitudes become lower with the increase of a distance from the cell center, approximately as 1IR. Under the action of electric fields the currents become to flow along the whole perimeter of a cell current channel. These currents are in some aspect similar to halo-currents arising in the plasma of tokamak during a pulsed ohmic current. When the cell current grows, the ¿halo¿ currents are directed oppositely to the cell current, i.e. electrons are moving to the cathode and ions are accelerated to the anode. When the cell current decreases, the induced electric field causes an antoelectronic emission from the cathode surface. The emitted electrons move along cycloids in the direction to the cell center making the gas desorption and building up the near-surface plasma (aureole) around the cell. Within the framework of this model it is possible to explain qualitatively many observed experimental facts: appearance of a weak glow around the cathode spot, division of cathode spots, the spot motion in the tangential magnetic field, etc.