Charging of Dust Grains in a Plasma

Charging of micron-sized dust grains in a plasma has been investigated experimentally. Dust grains were dispersed into a fully ionized, steady-state, magnetized plasma column consisting of electrons and ${\mathrm{K}}^{+}$ ions, both at a temperature of \ensuremath{\cong}0.2 eV. Langmuir probe measurements were used to determine how the negative charge in the plasma is divided between free electrons and dust grains. By varying the ratio $\frac{d}{{\ensuremath{\lambda}}_{D}}$ between the intergrain spacing and the plasma Debye length, the predicted reduction in the grain charge for the case of "closely packed" grains $\frac{d}{{\ensuremath{\lambda}}_{D}}<1$ has been demonstrated experimentally.