Parallel electric fields in nonlinear magnetosonic waves in an electron-positron-ion plasma

The electric field E_parallel along the magnetic field B in nonlinear magnetosonic waves in a three-component plasma is studied with theory based on a three-fluid model and with fully kinetic, electromagnetic, particle simulations. The theory for small-amplitude (ε<<1) pulses shows that the integral of E_parallel along B, F=-∫E_parallelds, is proportional to ε(p_e0-p_p0) in warm plasmas, where p_e0 and p_p0 are, respectively, the electron and positron pressures, and proportional to ε²m_iv_A²/(1+v_A²/c²)³ in cold plasmas, where v_A is the Alfven speed. These predictions are verified with simulations. Furthermore, for shock waves with ε∼O(1), simulation values are consistent with the phenomenological relation n_e0eF∼ε(ρv_A²+Γ_ep_e0)(n_i0/n_e0), where ρ is the mass density and Γ_e is the specific heat ratio. These results indicate that E_parallel can be strong in strong magnetic fields