Conditions for the formation of nongyrotropic current sheets in slowly evolving plasmas

Schindler, Karl; Hesse, Michael
August 2010
Physics of Plasmas;Aug2010, Vol. 17 Issue 8, p082103
Academic Journal
This paper addresses the formation of nongyrotropic current sheets resulting from slow external driving. The medium is a collisionless plasma with one spatial dimension and a three-dimensional velocity space. The study is based on particle simulation and an analytical approach. Earlier results that apply to compression of an initial Harris sheet are generalized in several ways. In a first step a general sufficient criterion for the presence of extra ion and electron currents due to nongyrotropic plasma conditions is derived. Then cases with antisymmetric magnetic and electric fields are considered. After establishing consistency of the criterion with the earlier case, the usefulness of this concept is illustrated in detail by two further particle simulations. The results indicate that the formation of nongyrotropic current sheets is a ubiquitous phenomenon for plasmas with antisymmetric fields that have evolved slowly from initial gyrotropic states. A fourth case concerns a plasma with a unidirectional magnetic field. Consistent with the general criterion, the observed final state is fluidlike in that it is approximately gyrotropic. Momentum balance is shown to include a contribution that results from accumulation of an off-diagonal pressure tensor component during the evolution. Heat flux also plays an important role.


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