The two-dimensional spatial and temporal evolution of a plasma
an electrode whose potential is suddenly decreased is experimentally investigated.
The electrode contains a localized convex or a localized concave
perturbation. The quasineutral plasma consists of positive ions and various
proportions of negative ions and electrons. The results are compared and
contrasted with those that are obtained numerically using a particle-in-cell
(PIC) simulation and those that had previously been obtained using a fluid-model