Strong Coulomb Coupling Influences Ion and Neutral Temperatures in Atmospheric Pressure Plasmas

TL;DR

This study uses molecular dynamics simulations to show that strong Coulomb coupling significantly affects ion and neutral temperature dynamics in atmospheric pressure plasmas, revealing rapid heating, relaxation, and recombination effects.

Contribution

The paper introduces an analytic model of temperature evolution that accounts for strong Coulomb coupling effects in atmospheric pressure plasmas, validated by simulations.

Findings

Ion-ion interactions are strongly coupled at low ionization fractions.

Disorder-induced heating rapidly increases ion temperature.

Ion-neutral collisional relaxation occurs over nanoseconds.

Abstract

Molecular dynamics simulations are used to model ion and neutral temperature evolution in partially-ionized atmospheric pressure plasma at different ionization fractions. Results show that ion-ion interactions are strongly coupled at ionization fractions as low as 10^-5 and that the temperature evolution is influenced by effects associated with the strong coupling. Specifically, disorder-induced heating is found to rapidly heat ions on a timescale of the ion plasma period (~10s ps) after an ionization pulse. This is followed by the collisional relaxation of ions and neutrals, which cools ions and heats neutrals on a longer (~ns) timescale. Slight heating then occurs over a much longer (~ 100s ns) timescale due to ion-neutral three-body recombination. An analytic model of the temperature evolution is developed that agrees with the simulation results. A conclusion is that strong coupling effects are important in atmospheric pressure plasmas.