Stationary waves in a bi-ion plasma transverse to the magnetic field

We investigate the nature of stationary structures streaming at subfast mag netosonic speeds perpendicular to the magnetic field in a bi-ion plasma con sisting of protons and a heavy ion species in which the magnetic field is f rozen into the electrons, whose inertia may be neglected. The study is base d on the properties of the structure equation for the system, which is deri ved from the equations of motion and the Maxwell equations, and therefore r eflects the coupling between the two ion fluids and the electrons through t he Lorentz forces and charge neutrality. The basic features of the structur e equation are elucidated by making use of conservation of total momentum a nd charge neutrality, which provide relations between the ion speeds in the unperturbed flow direction and the electron speed. This combination of rel ations, which we call the momentum hodograph of the system, reveals the str ucture of the flow and the magnetic field in a solitary-type pulse. In part icular, we find that in the initial portion of a compressive soliton, heavy ions run ahead of the electrons and the protons lag between them until a p oint is reached where they all once more attain the same speed, after which the protons run ahead and are accelerated whereas the heavies now lag behi nd the continuously decelerating electrons. The second half of the wave is a mirror image of the first portion. The strength of the compression (the a mplitude of the wave) is determined from the momentum hodograph, and depend s upon the initial Mach number, abundance ratio of heavies to protons and t he mass ratio. The analysis is relevant to subfast flows of mass-loaded pla smas and pile-up boundaries, which appear near comets and non-magnetic plan ets.