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 ${10}^{\ensuremath{-}3}$-2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ torr). These are compared with the predictions of a collisional-radiative model. For electron densities between ${10}^{13}$ and ${10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and electron temperatures in the range 700-2000\ifmmode^\circ\else\textdegree\fi{}K, the recombination coefficient is found to be in good agreement with theoretical values. It is proportional to ${{T}_{e}}^{\ensuremath{-}\ensuremath{\gamma}}$ with $\ensuremath{\gamma}=4.2\ifmmode\pm\else\textpm\fi{}0.4$. 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.