Increasing the oxygen dissociation degree in the plasma of a pulse-periodic Ar/O2 low-pressure arc

Abstract

The results of a study on O2 dissociation conditions in the near-anode area of forcibly compressed low-pressure arc discharge are presented. A combined mode of discharge operation was applied to increase the O2 dissociation degree. In this mode, high-current pulses (up to 160 A) of short duration (100 μs) were imposed on a direct current discharge (up to 70 A). Probe measurements showed that a higher atomic oxygen concentration is caused by increasing not only the electron current, but also the voltage drop in the anode part of the discharge in the pulsed phase. A necessary condition for achieving high average values of O2 dissociation degree at high pulse ratio is the increased lifetime of oxygen atoms in the volume. This condition is fulfilled in a gas-discharge system with metal walls used for the deposition of oxide coatings through formation on the walls of amorphous oxide films, which have a low atomic oxygen recombination coefficient. An O2 dissociation degree of ∼0.4 in a low-pressure arc (less than 1 Pa) in Ar/O2 mixture was obtained by optimizing the parameters of the arc operation mode and the condition of the wall surface of the gas-discharge system.