Interaction between dust grains near a conducting wall.pdf

a r X i v : p h y s i c s / 0 2 0 9 0 4 9 v 1 [ p h y s i c s .p l a s m - p h ] 1 2 S e p 2 0 0 2 Interaction between dust grains near a conducting wall A.M. Ignatov? Institute of General Physics, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia Abstract The effect of the conducting electrode on the interaction of dust grains in a an ion flow is discussed. It is shown that two grains levitat- ing above the electrode at the same height may attract one another. This results in the instability of a dust layer in a plasma sheath. 1 Introduction A good deal of experiments in dusty plasma physics are performed with aerosol grains suspended in the plasma sheath. A negatively charged dust grain in the sheath levitates above a horizontal electrode due to the balance of two forces: the gravity force directed downwards and the sheath electric field that pushes the grain upwards. The near-sonic or the supersonic ion flow in the sheath creates the wake field downstream of the grain. Since the latter is confined by a certain Mach cone, it is commonly accepted that the wake field affects the motion of grains, which are situated downstream only. The usual assumption is that the intergrain potential is smooth in the horizontal direction, i.e., two grains levitating at the same height repel one another via the screened Coulomb potential. The structure of the wake field and the grain interaction in an ion flow were studied in details [1-5]. The asymmetric interaction of vertically aligned grains was also observed experimentally [6]. ?e-mail: aign@fpl.gpi.ru 1 Analytical theory and computer simulations cited above assumed that the plasma density is constant and the influence of the conducting electrode is negligible. Although both assumptions evidently fail under conditions of a real plasma sheath, taking into account the plasma non-uniformity seems to be a very difficult problem. In order to estimate the influence of the electrode upon grain interaction, he