Collisional and Radiative Processes in a Cesium Afterglow

The evolution of electron density, electron temperature, and population of excited states is measured in a cesium afterglow (pressure range 10^-3-2 ×{} 10^-2 torr). These are compared with the predictions of a collisional-radiative model. For electron densities between 10¹³ and 10¹¹ cm^-3 and electron temperatures in the range 700-2000^∘{}K, the recombination coefficient is found to be in good agreement with theoretical values. It is proportional to Tₑ^-γ with γ=4.2±0.4. The model is shown also to predict accurately the evolution of the electron temperature and excited-state populations. In the late afterglow a change in the ambipolar-diffusion coefficient is observed and is interpreted to be due to a change in the majority ion.