Measurements of electron energy distributions in front of and behind a stationary plasma sheath

Abstract

Electron energy distributions have been measured in front of and behind a stationary plasma sheath in a low-pressure mercury discharge. The sheath appears at a constriction of the discharge tube. The measurements have been done with a small spherical probe, using the second-derivative method. The results show that the energy distribution of the anode side of the sheath is a sum of a maxwellian and an accelerated distribution. Near the sheath the accelerated electrons suffice to carry the discharge current, but far from it the current requires anisotropy in the thermal part of the distribution function.