New aspects of the Jeans instability in dusty plasmas

In contrast to a gas, a dusty plasma can support a variety of wave modes each in principle able to impart to the dust grains the randomising energy-necessary to avoid Jeans collapse on some length scale. Consequently, the stability to Jeans collapse is more complex in a dusty plasma than it is for a charge-neutral gas. After recalling some of the fundamental ideas related to the ordinary Jeans instability in neutral gases, we will extend the discussion to plasmas containing charged dust grains. Besides the usual Jeans criterion based upon thermal agitation, various other ways of countering the gravitational collapse can be considered. One is via excitation of electrostatic dust-acoustic modes, the other via novel Alfven-Jeans instabilities for perpendicularly propagating electromagnetic waves on the extraordinary mode branch. The wavelengths that are unstable are modified due to the presence of a magnetic field and of charged particles. These mechanisms yield different minimum threshold length scales for the onset of instability/condensation.