Instabilities, waves, and nonequilibrium structures in a dense low-frequency plasma (a look at the problem after 50 years publications in the journal High Temperature)

This review is devoted to one of the fundamental problems of plasma physics, namely, waves and instabilities in a dense low-temperature plasma. Instabilities are characteristic of a large number of natural phenomena. They affect the existence of nonequilibrium systems and cause a transition from one state to another. Ensuring stability of a process is the central problem in many technologies in which a low-temperature plasma is used as an working medium. This review is aimed at revealing the key mechanisms which lead to instabilities and at presenting the instability criteria in a clear physical form. A method that allows considering the modern state of the problems of instabilities and propagation of waves with a specified wave number in a dense low-temperature plasma of gases and metal vapors from a unified standpoint is discussed. Acoustic, overheating, current-convective, ionization, and ionization-field instabilities are considered in detail. This study is performed in the framework of continuum models both for a dense plasma in which the temperatures of electrons and heavy particles (atoms and ions) do not almost differ ($T_a\approx T_e$) and a plasma in which the electron temperature differs from the temperature of heavy particles ($T_a\ne T_e$). Particular attention is given to the effects of the Ampere force, Joule heating, and the processes related to changes in the plasma composition (ionization and recombination) and the energy exchange between the plasma components in the absence of temperature equilibrium. The contribution of the half-century publications in High Temperature to investigation of this problem is traced.