Field structure of large-amplitude magnetohydrodynamic waves and associated ultrarelativistic particle acceleration

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In the ideal magnetohydrodynamics, the electric field parallel to the magnetic field is exactly zero, and it was generally thought that the parallel electric field was quite weak in low-frequency, long-wavelength phenomena in a collisionless plasma. We have found, however, that the parallel electric field can be quite strong in nonlinear magnetosonic waves : We have analytically obtained the parallel electric field in nonlinear magnetosonic waves and have quantitatively confirmed the theoretical prediction with relativistic, fully kinetic, fully electromagnetic particle simulations.We have also numerically studied the evolution of magnetohydrodynamic waves arising from a strong disturbance given to a collisionless plasma. Simulations show that large-amplitude Alfven waves are generated behind magnetosonic shock fronts. Furthermore, ultrarelativistic electron acceleration can occur in the Alfven wave region. These mechanisms have been theoretically analyzed in detail.