Non-equilibrium in low-temperature plasmas

Abstract: The wide range of applications of cold plasmas originates from their specialcharacteristic of being a physical system out of thermodynamic equilibrium. This propertyenhances its reactivity at low gas temperature and allows to obtain macroscopic effectswith a moderate energy consumption. In this review, the basic concepts of non-equilibriumin ionized gases are treated by showing why and how non-equilibrium functions of thedegrees of freedom are formed in a variety of natural and man-made plasmas with particularemphasis on the progress made in the last decade. The modern point of view of a molecularbasis of non-equilibrium and of a state-to-state kinetic approach is adopted.Computational and diagnostic techniques used to investigate the non-equilibrium conditionsare also surveyed. Graphical abstract: [Figure not available: see fulltext.]