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Departure from MHD prescriptions in shock formation over a guiding magnetic field

  • A. Bret (a1) (a2), A. Pe'er (a3), L. Sironi (a4), M.E. Dieckmann (a5) and R. Narayan (a6)...


In plasmas where the mean-free-path is much larger than the size of the system, shock waves can arise with a front much shorter than the mean-free-path. These so-called “collisionless shocks” are mediated by collective plasma interactions. Studies conducted so far on these shocks found that although binary collisions are absent, the distribution functions are thermalized downstream by scattering on the fields, so that magnetohydrodynamics prescriptions may apply. Here we show a clear departure from this pattern in the case of Weibel shocks forming over a flow-aligned magnetic field. A micro-physical analysis of the particle motion in the Weibel filaments shows how they become unable to trap the flow in the presence of too strong a field, inhibiting the mechanism of shock formation. Particle-in-cell simulations confirm these results.


Corresponding author

Address correspondence and reprint requests to: A. Bret, ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain and Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real, Spain. E-mail:


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Departure from MHD prescriptions in shock formation over a guiding magnetic field

  • A. Bret (a1) (a2), A. Pe'er (a3), L. Sironi (a4), M.E. Dieckmann (a5) and R. Narayan (a6)...


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