The amount of metal evaporating from the cathode spot (Part 2).

Since the total length of the cathode zone (the ionization zone and the free-motion zone of the ions adjacent to the cathode surface) is several mean free paths of atoms, we can assume that the concentration of iron atoms in the entire cathode zone is approximately equal to the concentration of atoms in the column of the arc and, taking that the flow of iron atoms emerging from the cathode zone displaces the atoms of the protective gas from the cathode spot, we can assume that the cathode zone is almost completely filled with only atoms of the cathode material, and the ion current in it is almost completely transferred by ions formed from the atoms of the cathode.

It should be especially noted that the impulse directed into the inside of the cathode and produced by the cathode upon evaporation of that part of the atoms that is ionized in the cathode zone will be completely compensated by a pulse directed toward the column of the arc when these atoms (ions) are braked in the electric field by the cathode zone from Vа to 0, and therefore this part (Ni) of the evaporated atoms does not cause the cathode (droplets) to move in space, since the resultant force is zero. The similar conclusion can also be drawn by taking into account the collisions of these atoms with atoms and ions in the cathode zone. In addition, it should be noted that the effect of the atoms of iron (Nп)  evaporating and leaving the cathode zone on the cathode reduces to the following. The amount of motion that they reported to the cathode upon evaporation is equal to NпmFeVа. Exactly the same, but the oppositely directed amount of motion these atoms carry with them (–NпmFeVа). The part of this amount of motion evaporates the atoms (Nп) to atoms moving to the cathode spot from the column of the arc during collisions, i.e. In the ionization zone, reducing their amount of motion, which they would transmit to the cathode upon impact against its surface. The amount of motion carried away from the cathode zone by evaporated Nп atoms is equal to Gп*V, where V — the escape velocity of the evaporated atoms from the cathode zone, it is this part of the momentum that will exert a force effect on the drop. The amount of motion equal to NпmFeVа – GпV will remain in the cathode zone and will be transferred to atoms moving from the arc column to the cathode spot as a result of their thermal chaotic motion, which will reduce their amount of motion in this direction by the amount NпmFeVа – GпV, and hence their force effect on the cathode, which, as it were, will somewhat reduce the atmospheric pressure under the cathode spot, since the atmospheric pressure manifests itself precisely in the transfer of momentum by atoms striking the surface of any object as a result of their thermal chaos movement. However, this decrease by the amount of NпmFeVа – GпV will be compensated by the amount of motion transferred to the cathode by the evaporated atoms (Nп) during evaporation, and the resulting amount of motion that the cathode will receive is determined by the difference NпmFeVа – (NпmFeVа – GпV) = GпV. Exactly, the amount of motion that uncompensated power action exerts on a drop.

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