Date of Award

Winter 1993

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Richard L Kaufmann

Abstract

The purpose of this study is to gain physical insight into how charged particles, which violate the guiding center approximations, contribute to cross-tail current in a self-consistent plasma sheet. A technique to generate self-consistent one-dimensional (1-D) current sheets is described. Groups of monoenergetic protons are followed in a model magnetic field. The sample current sheets are characterized by resonant quasiadiabatic and stochastic orbits. The magnetic moment of a quasiadiabatic ion which is injected from outside a current sheet changes substantially during an interaction with the current sheet, but returns to almost its initial value by the time the ion leaves. The resonant nature of the interaction is associated with a strong energy dependence. The magnetic moment of a stochastic ion changes substantially during an interaction with the current sheet. Several ion and electron groups are combined to produce a plasma sheet in which the charged particles carry the currents needed to generate the magnetic field in which the orbits are traced. An electric field also is required to maintain charge neutrality. Three distinct orbit types, one involving untrapped and two composed of trapped ions, are identified. Each class of ions carries a qualitatively different current distribution. Contributions from all three groups are needed when resonant ions are used to generate a typical quiet-time self-consistent current sheet. It was found that self-consistent current sheets can not be generated using only stochastic ions. A relatively small density of resonant protons must be added to a current sheet in which stochastic ions dominate. Distribution functions are evaluated so that the expected count rates and several fluid parameters could be plotted. Limitations associated with the use of a 1-D model also are investigated. It is found that the model can provide a good physical picture of an important component of the cross tail current. However, we conclude that 1-D models cannot adequately describe any region of the magnetotail in which the principal current sheet is separated from the plasma sheet boundary layer by a nearly isotropic outer portion of the central plasma sheet.

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