Cathode Region of a Steady-state Townsend Discharge in Nitrogen

Abstract

The photon flux technique has been used to study the cathode region of a steady-state Townsend discharge. Spatial variations in the radiation emitted from the C3fIu and B2.r~ states of molecular nitrogen were detected in the vicinity of the cathode for EIN"" 331 and 555 Td. In particular, the second positive emission at 337·1 nm is similar to the Holst-Oosterhuis layers observed in rare gas discharges. Monte Carlo simulations describe qualitatively the experimental results. However, modification of the assumed cross sections is required to improve quantitative agreement between simulation and experiment.

Comparison of the results of Monte Carlo simulations with experimental data for electron swarms in from moderate to very high electric field to gas density ratios

“…Following the pioneering work of Itoh and Musha [6], Monte Carlo simulations of electron swarms have been used to verify the high accuracy of numerical solutions to the Boltzmann equation [7][8][9], to obtain cross sections from the transport data [10], to study the non-equilibrium regions close to the metal electrodes [11,12] and transitions in inhomogeneous fields [13], to point out some inaccuracies or oversimplifications in basic definitions of the transport coefficients and numerical approaches to their calculation [7,14,15], and to try to represent realistically experimental situations which are more complex than the theory used to analyse them [16]. There have been limited attempts to obtain numerical solutions for the Boltzmann equation in the neighbourhood of absorbing electrodes [17], but in principle the difficulties in such an approach are great whereas Monte Carlo simulations are ideally suited for that purpose.…”

A Monte Carlo Investigation of E x B Discharges in Molecular Nitrogen

“…This behaviour has been observed both experimentally (see e.g. Kelly et al 1989;Fletcher 1985) and in many simulations (Hayashi 1982;Marode and Boeuf 1983;Amies et al 1985), so that care must be taken in defining 'equilibrium', or steady state conditions.…”

“…In this purely theoretical study, we have adopted set C from Tagashira et al (1980) and modified the set to include an excitation to the B2 2:~ state of nitrogen (Stanton and St. John 1969) and a dissociative ionisation cross section (E. E. Kunhardt, personal communication 1983). This was performed in such a way that the sum of the ionisation cross sections was identical to that by Tagashira et al These alterations to the model allow comparison with the experiments of this laboratory (Kelly et al 1989;Wedding and Kelly 1989), some of which have observed transitions from the B2 ru state.…”

“…Experiments in Ex B fields are being conducted in these laboratories using the 'photon flux' technique (Blevin 1985). Since these experiments are also capable of yielding information about electrode boundary regions (Blevin et al 1985;Kelly et al 1989), the Monte Carlo method was chosen for the theoretical study to augment our understanding of experimental details. This paper 0004-9506/90/010027$03.00 describes some features of the simulation technique, developed to optimise the simulation of a 'many process' gas model, and examines the influence of gradients in the electron concentration on phenomena associated with Ex B discharges.…”

Optical Studies of Pre-breakdown Electron Avalanches

“…This spatial variation in the distribution function was confirmed by observing the 337 ·1 and 391·4 nm radiation from discharges in a C02:N2:He:CO (6:34:54:6) gas mixture. Abel inversion of the integrated line of sight data showed a strong radial dependence in the ratio of excited state populations (Wedding and Kelly 1989). An example of the radial dependence of these emissions is shown in Fig.…”