Dust acoustic waves in strongly coupled dusty plasmas

Abstract

Dust grains, or solid particles of \ensuremath{\mu}m to sub-\ensuremath{\mu}m sizes, are observed in various low-temperature laboratory plasmas such as process plasmas and dust plasma crystals. The massive dust grains are generally highly charged, and it has been shown within the context of standard plasma theory that their presence can lead to new low-frequency modes such as dust acoustic waves. In certain laboratory plasmas, however, the dust may be strongly coupled, as characterized by the condition ${\ensuremath{\Gamma}}_{d}{=Q}_{d}^{2}\mathrm{exp}(\ensuremath{-}d/{\ensuremath{\lambda}}_{D}{)/dT}_{d}>~1,$ where ${Q}_{d}$ is the dust charge, $d$ is the intergrain spacing, ${T}_{d}$ is the dust thermal energy, and ${\ensuremath{\lambda}}_{D}$ is the plasma screening length. This paper investigates the dispersion relation for dust acoustic waves in a strongly coupled dusty plasma comprised of strongly coupled negatively charged dust grains, and weakly correlated classical ions and electrons. The dust grains are assumed to interact via a (screened Coulomb) Yukawa potential. The strongly coupled gas phase (liquid phase) is considered, and a quasilocalized charge approximation scheme is used, generalized to take into account electron and/or ion screening of the dust grains. The scheme relates the small-$k$ dispersion to the total correlation energy of the system, which is obtained from the results of published numerical simulations. Some effects of collisions of charged particles with neutrals are taken into account. Applications to laboratory dusty plasmas are discussed.