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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 1:32 |
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Conference: Bucharest University Faculty of Physics 2006 Meeting
Section: Optics, Spectroscopy, Plasma and Lasers
Title:
Charged particles distributions injected into a
one-dimensional tangential discontinuity
Authors:
Gabriel Voitcu1, Costel Bunescu1, Marius M. Echim1,2
Affiliation:
1Institute for Space Sciences, Magurele, Romania, gabi@venus.nipne.ro
2Belgian Institute for Space Aeronomy, Bruxelles, Belgium
E-mail
gabi@venus.nipne.ro
Keywords:
space plasma, tangential discontinuity, Vlasov equation, numerical simulation, magnetosphere.
Abstract:
Test particle simulations have been performed in order to obtain the velocity distribution functions of electron and proton clouds moving in the magnetic field of a one-dimensional tangential discontinuity. The aim is to derive an accurate description of the dynamics of a collisionless, low beta plasma in non-uniform electromagnetic fields. We use a steady state magnetic field distribution whose direction and magnitude change from B1 at the “left” hand side of discontinuity to B2 at the “right” hand side. The magnetic field may rotate with the shear angle . We assume different prescribed electric field distributions such that the condition E • B = 0 is satisfied everywhere. We report results obtained in two cases: (A) for an uniform electric field, as in steady-state models of magnetic reconnection; (B) for a non-uniform electric field that varies such that the electric (or zero order) drift is conserved everywhere. The particles are injected from sources aligned along the x-axis in the “left” hand side of the discontinuity. The initial velocities of the particles are distributed in the velocity space according to a displaced Maxwellian. The velocity distribution function (VDF) of electrons and protons are obtained as a function of x inside the simulation domain by solving the stationary Vlasov equation. The solution is found by integrating numerically the characteristics of the Vlasov equation. The latter coincide with the trajectories of the test-particles in the physical space. In the case of an antiparallel magnetic field distribution and a uniform electric field (case A) the simulations show the formation of a current sheet parallel to the discontinuity and centered in the B = 0 region. The distribution of the protons and electrons is highly anisotropic in the velocity and position space. The structuring, both in velocity and position space, has a much smaller scale for electrons than for protons. The VDF provided for different regions in physical space show the features imprinted in the particles distribution by the acceleration mechanism. For the same antiparallel magnetic field, but using a non-uniform electric field distribution (case B), the particles cloud penetrate the discontinuity and move across it into the “right” hand side. The results are relevant for experimental observations of non-gyrotropic VDFs in the tail of the Earth`s magnetosphere.
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