CHARGING OF DUST GRAINS IN PLASMA WITH ENERGETIC ELECTRONS

The charge on small grains of glass, copper, graphite, and silicon has been measured in a plasma device containing both thermal electrons wi th energies of a few eV and monoenergetic suprathermal electrons. For conditions in which the charging current is dominated by suprathermal electrons, the grains charge to the potential that repels these electr ons unless they induce significant secondary emission. The charge on t he grains is linear with size for diameters from 30 to 120 mu m and is the value expected from the grain capacitance and the charging potent ial.