Cooling and chemical kinetics in a wall-stabilized SF₆arc in extinction

Experimental results concerning the changes in temperature and particle densities in a SF 6 arc in extinction were compared with results obtained from modelling based on the hypothesis of thermal equilibrium. The model predictions for cooling rates were in agreement with experimental results. In particular, if the equilibrium is maintained, the time constant of the changes in electron density varies from 20 mu s to about 8 mu s when the arc diameter is reduced from 5 to 3 mm. Finally, a kinetic model showed that the mechanisms of electron/positive-ion recombination and of attachment are efficient enough to ensure the state of collisional equilibrium during arc extinction as long as the temperature is greater than 8000 K.