Observation of Spatial Variations in the Energy Distribution Function for Steady-state Townsend Discharges

Spatial variations of the relative excitation rates for two electronic states of molecular nitrogen have been measured for a point source Townsend discharge. The ratio of these rates shows a spatial dependence which is explained in terms of an electron con,centration gradient expansion of the energy distribution function. The electronic states were chosen to have quite different thre hold energies such that the ratio would be sensitive to small changes in the electron energy distribution. A model for secondary electron production is used to explain the significant influence of secondary ectrons in the outer regions of the discharge.