Influence of the trapped ions on the screening effect and frictional force in a dusty plasma

The problem of screening of the charge acquired by a dust grain in a two-temperature plasma is considered. The influence of the trapped ions on the screening effect and on the frictional force exerted on a dust grain by an ion flow is investigated. It is shown that the ions trapped by a grain radically reduce the frictional force in the ion flow because their distribution is determined by the temperature of the cold buffer gas. The mechanism for the onset of the reactive force that accelerates the grain in the direction opposite to that of the flow is explained. It is based on the momentum transfer from the flow of the ions that are additionally accelerated in the grain field to the atoms of the buffer gas. As a result, the momentum carried by the charge-exchange atoms out of the “ions + grain” system exceeds the momentum they have carried into the system; this gives rise to a reactive force directed opposite to the ion flow (the negative frictional force). The magnitude of the reactive force is estimated.