Negative ion density fronts during ignition and extinction of plasmas in electronegative gases

Negative ion density fronts have been shown to occur in electronegative ste ady-state plasmas with hut electrons. In this Letter, we report theoretical and numerical results on the spatiotemporal evolution or negative ion dens ity fronts during plasma ignition and extinction (afterglow). During plasma ignition, the negative ion fronts are analogous to hydrodynamic shocks. Th is is not the case during plasma extinction where. although negative ions d iffuse freely in the plasma core, the negative ion front propagates towards the chamber walls with a nearly constant velocity.