STABILITY OF THE PLASMA-SHEATH

The existence, properties and structure of the sheath which forms adjacent to any surface in contact with a plasma have been studied in considerable detail in recent years. In the case of low density plasmas when recent years. In the case of low density plasmas when the space charge dominated region is of order of several Debye lengths thick and the charged particle motion collisionless, the requirement that the potential is monotonic leads to the Bohm criterion. This has been generalized to include an ion distribution1. The requirement imposed relates to spatial and not temporal variations and so the stability of the solution is not investigated