The expansion of polarization charge layers into a magnetized vacuum: Theory and computer simulations

Abstract

When a sufficiently dense plasma stream moves across a magnetic field, the stream will form polarization charge layers and will ExB drift across the field. One charge layer is composed of electrons and the other is composed of ions. The phenomena associated with the expansion of these polarization charge layers along the magnetic field away from the stream is investigated by means of analytic theory and is confirmed by two-dimensional electrostatic particle-in-cell computer simulations. At very early times, the expansion of the electron charge layer is described by single-particle motion in a dipolelike electric field. Eventually, the electron expansion is halted by the net positive charge left behind at the stream. Then an ambipolar expansion of the electron and ion charge layers forms, with the expansion velocity set by the stream voltage rather than by plasma temperatures. Steady decreases in the cross-field-propagation velocities of the streams are observed, owing to the steady losses of charge from the stream edges. © 1991 American Institute of Physics.