Arc Discharge Anode Reattachment: Simple Model

Anode attachment of a nontransferred dc arc moves along the anode nozzle. Under the influence of the gas flow, it moves downstream thus elongating the arc. This leads to an increase of the arc voltage. The voltage across the cold layer that separates the arc column and the nozzle increases accordingly. This voltage increase leads to the breakdown of the cold anode layer. After this breakdown, the anode attachment jumps to the new upstream location (reattachment). The phenomenon of reattachment of the anode spot has not been completely understood yet. A simple model of the reattachment is suggested. Based on a suggestion that electron temperature inside the cold layer does not drop as low as the heavy particles´ temperature does, it is assumed that some residue electrical conductivity (on the level of 10^-2 Ω^-1) exists in this layer. It is shown that the voltage drop across the layer rises in time, leading to a fast developing overheating instability. This creates a electrically conductive column at an upstream location and results in reconnection of the arc to this new anode location. Simple estimations of the amplitude of the voltage oscillations and their frequency correspond to the experimental data.