ABSTRACT
INTRODUCTION Recently, back-diffusion has had a renewed interest due to its importance in practical plasma devices such as plasma light sources, display panels [1], in studies of breakdown [2,3] and in nuclear particle detectors [4,5]. Both kinetic theory [1] and Monte Carlo simulations [5] have been applied with some success. However it seems that the primary aim in those studies has been either to produce simplified formulae for application in plasma modelling [1] or to obtain an agreement with the experimental data [5] without analyzing which aspects of the process are required to achieve good representation of the phenomenon. In this paper we perform a systematic study of various models of most aspects of electron back-diffusion. Standard theories of backdiffusion either belong to the ballistic (purely non-hydrodynamic) or hydrodynamic groups depending on the treatment of electron transport in the vicinity of the cathode. The best known theory, represented by the Thomson-Loeb equation has actually become successful only after Loeb modified Thomson's approach, which was purely ballistic, to make a combination of the two assumptions. The third approach was developed recently and it consists of full kinetic treatment either by solving the Boltzmann equation [1] or by performing Monte Carlo simulations (MCS) [6,7] A systematic study of the relationship between non-hydrodynamic behaviour and backdiffusion was not performed so far for nitrogen and in this paper we attempt to make such analysis. We have chosen nitrogen since one may expect great differences in equilibration distances in narrow E/N due to the resonance in vibrational excitation. Recently a revision of the standard Townsend's theory of breakdown at low pressures was completed and backdiffusion plays one of important parts in the
calculation of secondary electron yields from the cathode [3].
