Control of electron dynamics, radical and metastable species generation in atmospheric pressure RF plasma jets by Voltage Waveform Tailoring

Abstract

Atmospheric pressure capacitively coupled radio frequency discharges operated in He/N2 mixtures and driven by tailored voltage waveforms are investigated experimentally using a COST microplasma reference jet and by means of kinetic simulations as a function of the reactive gas admixture and the number of consecutive harmonics used to drive the plasma. Pulse-type ‘peaks’-waveforms, that consist of up to four consecutive harmonics of the fundamental frequency (f = 13.56 MHz), are used at a fixed peak-to-peak voltage of 400 V. Based on an excellent agreement between experimental and simulation results with respect to the DC self-bias and the spatio-temporal electron impact excitation dynamics, we demonstrate that Voltage Waveform Tailoring allows for the control of the dynamics of energetic electrons, the electron energy distribution function in distinct spatio-temporal regions of interest, and, thus, the generation of atomic nitrogen as well as helium metastables, which are highly relevant for a variety of technological and biomedical applications. By tuning the number of driving frequencies and the reactive gas admixture, the generation of these important species can be optimised. The behaviour of the DC self-bias, which is different compared to that in low pressure capacitive radio frequency plasmas, is understood based on an analytical model.

Kinetic Simulation of He radio frequency capacitively coupled plasma

“…The highest peak of the IAD belongs to case (3) and the lowest one is due to case (2). From previous calculations, increasing the ion flux, the sheath potential, and decreasing the sheath width allow high peak of the ion angular distribution [8]. This matches very well with case (3), please investigate Figs ( 1) and (2).…”

“…7 is higher than relevant peaks in Fig. (8). This means a larger occupation of bulk electrons in that energy range with respect to the electron occupation at the electrode.…”

“…Only for cases (1) and (2) at the electrode, the height and the width of the distribution increased by adding a phase shift of π/2. If we compare the peaks of the electron distribution in Figs (7) and (8), the peaks at energies roughly from 3 to 5 eV in Fig. 7 is higher than relevant peaks in Fig.…”

“…The driven frequencies are 60 MHz and 1 MHz. Tailoring the driven potential or driven electrodes with different radio frequencies is one of the hot topics of research nowadays [7,8,9].…”

Selective modulation of plasma parameters in an atmospheric dielectric barrier discharge driven by sawtooth-type tailored voltage waveforms

“…In 2019, Korolov et al used the tailored voltage waveform and also effective control of electron dynamics and metastable species generation at atmospheric pressure. [27][28][29] The above-mentioned modulation technology is still in its early phase of theoretical and laboratory studies, as well as feasibility studies for translation to other downstream technological applications. Associated modulation mechanisms still require significant and thorough investigation and analysis for clearer understanding of the physics involved.…”