High negative charge of a dust particle in a hot cathode discharge

Dust particle levitation experiments in a plasma produced by a hot filament discharge, operating at low argon pressure, are presented. The basic chara cteristics of a dust grain trapped in a plate sheath edge in these experime ntal conditions are reported. Taking into account the sheath potential prof iles measured with a differential emissive probe diagnostic, the forces app lied to an isolated dust grain can be determined. Two different experimenta l methods yield approximately the same value for the dust charge. The obser ved high negative charge is mainly due to the contribution of the primary e lectrons emitted by the filaments as predicted by a simple model. [S1063-65 1X(99)14611-7].