Evidence of Stochastic Diffusion Across a Cross-Field Sheath Due to Kelvin-Helmholtz Vortices
Abstract
We identify mechanisms for particle transport across a cross-field sheath. We present a study of E x B drift motion in a vortex in which the ion drifts are perturbed by their finite gyroradii and electron drifts are perturbed by one or more traveling waves. Large scale vortices, which are the result of nonlinear saturation of the Kelvin-Helmholtz instability resulting from shear in the E x B drift velocity, have been observed in plasma simulations of the cross- field sheath. Small scale turbulence is also present, and ions and electrons are transported across the sheath. A vortex alone does not allow for the observed electron transport because the electron drift orbits simply circulate. On the other hand, the ion motion can be stochastic from resonant interaction between harmonics of the drift motion and the gyromotion, independent of the background turbulence. The fluctuations in the ion density would then give rise to small amplitude wave spectrum. The combined action of the vortex fields and traveling wave fields on the electron motion can then lead to stochastic electron diffusion. We study these effects, showing that the values of vortex fields observed in the simulation are sufficient to lead to both ion and electron stochasticity. Furthermore, the rate of the resulting diffusion is sufficient to account for the diffusion observed in the simulation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 1991
- Accession Number
- ADA247847
Entities
People
- A. J. Lichtenberg
- Charles K. Birdsall
- S. E. Parker
- Xiang Xu
Organizations
- University of California, Berkeley