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Demagnetization of transmitted electrons through a quasi-perpendicular collisionless shock

Abstract : Physical processes responsible for the electron demagnetization within the front of a quasiperpendicular collisionless shock are analyzed via a comparative study between theoretical calculations and computer simulations. Herein, simulation results of a shock in supercritical regime are based on the use of a 2-D full particle self-consistent code. Present statistics on the spatial widths of the magnetic field (L Br) and electric field (L Er) within the ramp show that their ratio R = L Er /L Br is around 1; this value is appropriate to demagnetize electrons and to provide a resulting deviation from adiabaticity [Balikhin et al., 1998]. In order to verify this theoretical expectation, two complementary approaches are used. First, the deviation of the full electron gyroperiod from the magnetic gyroperiod is analyzed from the trajectories of ''marked'' self-consistent electrons crossing the shock ramp. In such a case, nonstationary and nonuniformity effects of the shock front are fully involved. Second, such effects are removed and test particles simulations are used in order to determine the strength of electron demagnetization when effects of width shock along the shock normal are included only. Both approaches confirm that demagnetization takes place within the first half of the ramp, that is, where the gradient dE lx /dx seen by transmitted electrons is positive. Statistical results performed using test particles simulations show that a noticeable number of demagnetized electrons are formed within the ramp even for a moderate supercritical Mach number and that the relative percentage of demagnetized/magnetized electrons varies according to the nonstationary behavior of the shock front (self-reformation).
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Philippe Savoini, M. Balikhin, S. Walker, V. Krasnoselskikh, Bertrand Lembège. Demagnetization of transmitted electrons through a quasi-perpendicular collisionless shock. Journal of Geophysical Research, American Geophysical Union, 2003, 108 (A6), ⟨10.1029/2002JA009288⟩. ⟨insu-03038933⟩



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