English: Illustration of the formation of a Debye sheath around a large positive charge in a plasma. Electrons cluster around the charge, while positive charges shy away from it. This creates a negatively charged cloud, called a sheath, that shields the rest of the plasma from the large positive charge's influence (i.e. it screens out the large positive charge). The dashed line represents the extent of the cloud, characterized by the Debye length λ. The plot at the bottom shows the electric potential generated by the large positive charge, which falls off as exp(−r/λ)/r (much steeper than the 1/r one would expect from an unscreened charge).