The Development of Two-Dimensional Structure in Cavitons.

Experimental observations of the space and time evolution of resonantly enhanced electric fields and plasma density in cylindrical geometry demonstrate the development of two-dimensional caviton structure when an initial density perturbation is imposed on the plasma in the direction perpendicular to the driver field. This two-dimensional structure is observed after the development of profile modification and grows on the ion time scale. The existence of a large azimuthal electric field component is an observational signature of two-dimensional structure. Enhanced electric field maxima are found to be azimuthally correlated with the density minima. Both the density cavities and electric field peaks exhibit increased azimuthal localization with the growth of two-dimensional structure. The two-dimensional development exhibits a strong dependence on both perturbation wavenumber and driver power. The related theoretical literature is reviewed and numerical and analytical models for a driven, two-dimensional, inhomogeneous plasma are presented. It is shown that the experimental results can be explained in a semi-quanitative manner by a model which combines the results of one-dimensional caviton theory with those of two-dimensional Langmuir collapse.