Cold discharge plasmas - Electrical properties

In nature, plasmas are the fourth state of matter after the solid, liquid and gaseous states.

The term plasma was introduced by Langmuir to designate the ionized gas produced in an electrical discharge and characterized by the behavior of charged particles (electrons and ions).

The term electrical discharge is used to describe any mechanism by which current flows through a gas. The term discharge originates from the fact that the first method of obtaining these currents was by discharging air-cooled capacitors. It has remained in common use ever since, even in the absence of actual charge transfer, as in the case of microwave devices.

Today, there is renewed interest in electrical discharges in gases, due to their potential applications or those already implemented in laboratories and industry. These applications make use of all or part of the species present in the plasma - electrons, ions, reactive neutral species - which are the agents of energy-efficient volume or surface physical chemistry.

Simultaneous advances in numerical modelling and experimental characterization techniques now make it easier to select a discharge and control its phenomenology, depending on the desired objective.

This article presents the basic concepts essential to low-intensity discharges (weakly ionized plasmas or cold plasmas) whose properties are dominated by the collisions of charged particles with the majority neutral atoms or molecules.