Gasplasma

Gas plasma is a partially ionized gas in which a significant fraction of atoms are ionized and electrons and ions coexist with neutral atoms. In a plasma, collective electric and magnetic fields couple the motions of charged species, giving rise to behaviors not found in neutral gases. Plasmas in gases typically have high electrical conductivity, emit light, and respond to electromagnetic fields. The degree of ionization can range from a small fraction to nearly complete, depending on the energy input and gas species. In high-temperature environments such as stars or fusion devices, plasmas can be largely or fully ionized; in laboratory and industrial contexts, many plasmas are only partially ionized or non-thermal.

Production and variants: Gas plasmas form when energy is deposited into a gas by electric discharges (glow, arc, corona), by radiofrequency or microwave fields, or by intense optical or particle irradiation. At atmospheric pressure, non-thermal (cold) plasmas can heat only electrons while keeping neutral species near room temperature, enabling surface treatment without bulk heating. Thermal plasmas reach higher temperatures and often operate at lower densities.

Properties: Plasmas exhibit Debye shielding, plasma oscillations, and collective effects. They emit characteristic spectra from excited atoms and ions and have high electrical conductivity. The presence of ions and reactive radicals makes plasmas highly reactive with many materials.

Applications: Plasmas are used in lighting (fluorescent lamps, neon signs), materials processing (etching, deposition, cleaning), surface modification, sterilization and disinfection, and environmental remediation. Gas-plasma displays were used in some flat-panel displays in the 1990s and early 2000s.