Electron energy distribution of a current-free double layer: Druyvesteyn theory and experiments.

Electron energy distributions upstream of a current-free double layer (CFDL) contained in a low-collisional plasma are modeled and compared with experimental results. The experimentally observed electron energy probability functions (EEPFs) with a depleted tail above the energy corresponding to the potential drop of the CFDL can be well approximated by a Druyvesteyn distribution function. Theoretical effective electron temperatures for the Druyvesteyn distribution are in good agreement with the values obtained from the experimental EEPFs over the range of pressure where the CFDL is observed.