Negative plasma potential in unmagnetized DC electropositive plasma with conducting walls

Negative plasma potentials were obtained in DC hot filament unmagnetized electropositive argon plasma for sufficiently low neutral pressure. Double layers provide ion and electron confinement near the walls. The potential profiles from the center of the plasma to the potential minima are quite similar in shape to those observed when the plasma has positive plasma potentials. The primary electrons emitted from the filaments are important for charge conservation and for modification of the Bohm criteria but are not important for current balance.

► Negative plasma potentials in plasmas that do not contain negative ions can exist. ► They are non-monotonic and bounded by double layers. ► It provides an explanation for unknown quality in hot filament discharges. ► Theory and experiment for double layers are given. ► Bohm speed modifications with the existence of external electrons are given.