Dust molecules and dust strings in dusty plasma

We show that, in the presence of ion flow, stable flow-aligned dust "molecules'' comprising up to four grains exist even in the absence of any con. ning force. These molecules propel themselves upstream, in apparent violation of energy and momentum conservation. Longer molecules are unstable. With a vertical con. ning potential, longer molecules are possible, but subject to hose instability at low pressure. With horizontal con. ning forces as well, multiple equilibria and hysteretic processes are possible. We show that the problem of two grains in a harmonic well can be reduced to Hamiltonian "single-particle'' form, permitting solution for ground and excited states.