Synergistic control of radical generation in a radio frequency atmospheric pressure plasma jet via voltage waveform tailoring and structured electrodes

TL;DR

This study demonstrates how combining tailored voltage waveforms with structured electrodes in RF atmospheric-pressure microplasmas enables spatially selective radical generation, enhancing control over plasma processes.

Contribution

It introduces a novel approach of waveform and electrode structuring synergy to achieve localized radical production in RF microplasmas.

Findings

Asymmetric waveforms localize electron power absorption.

Structured trenches focus radical generation spatially.

Reversible control of plasma activity at specific electrode regions.

Abstract

The synergy between voltage waveform tailoring and structured electrodes is investigated in a radio-frequency (RF) atmospheric-pressure microplasma jet operated in helium with a 0.1% oxygen admixture. The device incorporates rectangular trenches in both electrodes and is driven by "Peaks" and "Valleys" waveforms synthesized from four harmonics (base frequency $f_{\rm b} = 13.56$~MHz, $V_{\rm pp} = 500$~V, $P=$1.2~W). Two-dimensional plasma fluid simulations, together with spatially and temporally resolved optical diagnostics (Phase-Resolved Optical Emission Spectroscopy and Tunable Diode Laser Absorption Spectroscopy), are used to demonstrate that the combination of asymmetric voltage waveforms with electrode structuring leads to strong spatial localization of electron power absorption and radical generation. This synergy results in a single pronounced maximum inside a trench at either the powered or grounded electrode, depending on the applied waveform, unlike a symmetric excitation, which produces a spatially symmetric enhancement at both electrodes. The effect is attributed to the interplay between waveform-induced sheath dynamics and geometric focusing provided by the trenches, enabling electrically reversible and selective enhancement of electron power absorption at a chosen location.