The structure and dynamics of electrostatic and magnetostatic drift holes

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Abstract
Localized, nonwavelike phase-space density fluctuations with self-trapping potentials, called drift holes, are studied for systems with density gradients. The three-dimensional structure of maximally probable, isolated electrostatic drift holes is determined and shown to satisfy a condition for self-trapping. The dynamics of such structures is examined. It is shown that under a broad set of conditions the potential amplitude, hole depth, and velocity-space width grow nonlinearly while maintaining the self-trapping structure. The nonlinear instability responsible for growth requires dissipative coupling between the trapped particles and the passing particles of the opposite species. Two saturation mechanisms for this instability are described and saturated amplitude estimates are given. It is shown that when the hole velocity is small compared to the speed of light, self-consistent coupling of stationary magnetic perturbations to the electrostatic potential is possible and produces structures called magnetostatic drift holes. The role of electrostatic and magnetostatic drift holes as a constituent of intermittent plasma turbulence is discussed.