Comparison between electropositive and electronegative cold atmospheric‐pressure plasmas: a modelling study

Abstract

Cold atmospheric-pressure He + N 2 and He + O 2 plasmas are chosen as the representatives for electropositive and electronegative plasmas, of which the discharge characteristics are studied and then compared to each other by fluid models. As the increase of the impurity (N 2 or O 2) fraction from 0 to 10%, for He + N 2 plasmas the electron density and ion density increase, the spatiotemporal distributions of electron density, ion density, electron temperature and electron generation rate change a little. On contrast, for He + O 2 plasmas the electron density decreases, the ion density first increases and then decreases, the electron temperature increases in the bulk region, but decreases in the sheath region, and the plasmas transform from g mode to α mode as the significant change of electron generation rate distributions. Larger electric field is needed in the bulk region to sustain the electronegative plasma, so the electrical characteristics of He + O 2 plasmas transform form capacitive to resistive with increasing O 2 fraction. Meanwhile, the ion-coupling power increases dramatically, which can be estimated by a formula based on the electronegativity. A new criterion for determining the sheath boundary, |∇E| = 5 kV/cm 2 , is put forward, which is found suitable for both the electropositive and electronegative plasmas.

Atomic oxygen generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and O2

“…This is similar to observations in low pressure oxygen discharges, where at specific conditions and due to the increasing electronegativity the electron density inside the bulk region is almost constant [99][100][101][102]. At high oxygen admixtures, due to the enhanced electronegativity, the electron density decreases sharply [98] and, therefore, a stronger bulk electric field is generated to sustain the plasma. In such strong electric fields, the electrons gain more efficiently energies needed to produce atomic oxygen.…”

“…Due to the electronegative nature of oxygen [97], at higher oxygen admixtures the excitation pattern inside the bulk also changes (see figures 8(a)-(c), orange arrows '2'), showing a transition from an electropositive plasma (similar to He/N 2 mixtures [49]) to an electronegative plasma [98]. The excitation maxima move from the expanding sheath edge (at 0.05% O 2 ) to the collapsing sheath edge (at 0.5% O 2 ).…”

Physicochemical properties of the AC-excited helium discharges using a water electrode

“…through the Penning ionization (R6) [34,35]. The OH (A-X) band can be produced from the dissociative electron recombination of H 2 O + (or H 3 O + ), and with the dissociative electron recombination which leads to production of OH (X), and then, to excitation to OH (A) through the electron impact reaction ((R7)-(R9)) [36].…”

Global model of plasma‐activated water over long time scale: Pulsed discharge and afterglow

“…Liu et al. explored the polarity effect and the effect of gas purity of helium plasma by a 2D model [25]. Tian et al.…”

“…Several numerical models such as 2D fluid model or hybridmodel have been developed to study plasma-liquid interactions. Liu et al explored the polarity effect and the effect of gas purity of helium plasma by a 2D model [25]. Tian et al investigated DBD discharge in wound treatment by a 2D simulation model [26].…”