The plasmadynamics of a stationary plasma thruster (SPT-100) plume in the
very-near-field region have been studied by using a two-dimensional
axisymmetric numerical code based on a combination of Particle-in-Cell (PIC)
simulation for ion component (Xe+ and Xe++) and fluid description
for electrons. In particular we have solved the electron momentum
conservation equation (including collisional and magnetic effects) and the
electron energy conservation equation (including collisional effects). Due
to the difference between electron and ion Larmor radius and to the effect
of the thruster wall, the quasi-neutrality hypothesis can be violated in the
very-near-field plume region and the electric field must be computed
accordingly. The xenon atom flowfield is calculated analytically. The model
allows a unitary rationalization of several experimental observations.