Comments on "On asymptotic matching and the sheath Edge"

In Sternberg and Godyak (2003), the authors claim that the sheath edge obtained through asymptotic matching is the edge of the electron free ion sheath characterized by Godyak\´s "strong" electric field |E|=kT_e/(eλ_D). I present a careful re-analysis of the same problem and show that the paper is incorrect. The "intermediate region" of asymptotic analysis has an extremely narrow validity range in potential space and does not contain the ion-electron sheath. Consequently, in asymptotic theory, the sheath edge is uniquely defined by the transition from the quasi-neutral plasma to the ion-electron sheath. It may equivalently be characterized by the Bohm criterion or by a "medium" electric field |E|∼kT_e/(eL³5/λ_D²5/) mediating between strong sheath fields |E|∼kT_e/(eλ_D) and weak plasma fields |E|∼kT_e/(eL).