Multistep ionization in the positive column of low‐pressure Na‐Ne and Ne discharges

摘要

Model calculations on the positive column of low‐pressure metal‐vapor–noble‐gas and noble‐gas discharges usually account for direct and two‐step electron‐impact ionization. The poor agreement between experiment and model calculations for certain discharge conditions has led us to a detailed analysis of the ion formation in a metal‐vapor–noble‐gas (Na‐Ne) and a noble‐gas (Ne) positive column. Multistep electron‐impact ionization via many higher excited states is found to become a dominant process already at much lower pressures and current densities than considered so far. The multistage ionization will have the effect of lowering the electric field strength. Its highly nonlinear dependence on discharge current will further strongly favor the contraction observed, e.g., in noble‐gas discharges.