Where is the 'sheath edge'?

Recent confirmation of the plasma–sheath structure and the associated plasma balance equation found some years ago for collisionless-plasma–collisionless-sheath, forms the basis for the examination of the nomenclature used to describe the structure of the plasma–sheath.

The fact that there is a transition layer between plasma and sheath when the sheath is collisionless means that there are clearly defined and separate 'points' which might conveniently be described as 'the plasma edge' and 'the sheath edge', being the beginning and the end of the transition region respectively. This suggests re-labelling the point that Tonks and Langmuir called the sheath edge.

Once this is done the controversy that has been raging over the past 13 years is resolved, and the different results obtained by different workers can be seen to fit into a harmonious whole.