Complex Plasmas: I. Complex Plasmas as Unusual State of Matter

This paper opens a series of review papers devoted to the physics of the so-called complex plasmas. The review contains a description of new physical phenomena met in dusty plasmas and complex plasmas. The term complex plasma is used for a state where some components (dust) are in crystal or liquid state, while the others (electron, ions, and neutral atoms) are in gaseous state. Experimental and the theoretical investigations of such a complex state of matter are presented. It is emphasized that (i) complex plasma represents quite an unusual state of matter, (ii) the system of dust grain cannot be considered as a Coulomb system, because it always has long-range and nonscreened interactions between the grains both of repulsive and attractive type and because the shielding of the grains is always nonlinear, (iii) the interactions between the particles in complex plasmas and in usual matter differ substantially due to strong plasma absorption on grains and the necessity to support the plasma density by an external source of ionization, (iv) the usual concept of free energy is not applicable to complex plasmas, because it is actually an open system, and (v) the collective nature of pair dust interaction is one of the most important new features of complex plasmas. The theory of elementary processes in complex plasmas, including these new phenomena, can be used to explain existing experiments on dust-plasma crystals, dust clusters, and waves and instabilities in complex plasmas.