Self-consistent Monte-Carlo simulation of the positive column in Argon
  A high accurate self-consistent Monte-Carlo method including charged and neutral particle motion and resonance photon transport is developed and applied to simulation of positive column discharge in Argon. The distribution of power loss across the tube is investigated. It is shown that negative slope of current-voltage gradient curve can not be explained by only one factor. Diffusion of metastable atoms to the tube wall in the case of low current ($0.2-3$mA) responds for the most part of negative slope. For the high currents the variation of radiation power loss makes a main contribution to the amplitude of negative slope. 
V.Zhakhovskii, and K.Nishihara