Planar plasma source and a floating wall

The Debye sheath that forms at the plasma-wall interface is discussed by means of the one dimensional collisionless kinetic model. We pay special attention to the simplification often adopted both in theoretical descriptions and numerical simulations, treating the wall as a perfect absorber. We show that this assumption, although it greatly simplifies the considerations, is too restrictive from the physical point of view as it leads to an overdetermined problem. This becomes somewhat understandable if we notice that this assumption does not allow for taking into account any properties of the wall.