The role of volume recombination and resonance radiation transport in constriction of a: DC discharge in argon

Abstract The work is aimed at revealing the influence of volume recombination on the formation of plasma parameters on the example of a diffuse and constricted positive column of a DC discharge in argon depending on the discharge current at pressures of 100–300 Torr·cm. At a qualitative level, the limiting transitions from the diffusion mode to the recombination mode of discharge maintenance are analyzed, which lead either to a rectangle-shaped radial profile of charged particles (arc discharge) or to a compressed profile (constricted discharge). Valuable information about the processes occurring in the plasma volume can be obtained from the ion current flowing toward the wall of the discharge tube since it is determined as a difference between the volume ionization and recombination. Based on a collision-radiative model, the ion current towards the tube wall was calculated and compared with the experimental results of probe measurements. In a diffuse discharge (low discharge current) a satisfactory agreement between the theory and experiment is observed. After the abrupt transition to the constricted regime (high discharge current), the theoretical values become strongly underestimated, and not able to describe the experimental data. The reasons for these discrepancies are analyzed. It is shown that the photoemission from the surface of the probe under the action of resonance photons gives an additional ion probe current which allows eliminating the discrepancies between the theory and experiment. Based on the Holstein–Biberman equation, the influence of the resonance radiation trapping on the discharge properties is revealed. The account of radiation trapping improves the agreement between the theory and experiment, including the values of the critical discharge currents at which the constriction occurs.