  Charge separation effects in the expansion of magnetized relativistic
electron-ion plasmas into a vacuum are examined using 2-1/2-dimensional
particle-in-cell plasma simulations. The electrostatic field at the plasma
surface decelerates electrons and accelerates ions. A fraction of the surface
electrons are trapped and accelerated by the pondermotive force of the
propagating electromagnetic pulse, a mechanism we call the DRPA (diamagnetic
relativistic pulse accelerator). This charge separation is enhanced as the
initial plasma temperature is decreased. The overall energy gain of the plasma
particles through the expansion strongly depends on the initial plasma
temperature. Moreover, the electrons become relatively less energized and the
ions more energized as the plasma temperature decreases.
