Micro atmospheric pressure plasma jets excited in He/O₂ by voltage waveform tailoring: a study based on a numerical hybrid model and experiments

Abstract

A hybrid simulation code is developed to treat electrons fully kinetically by the particle-in-cell/Monte Carlo collision (PIC/MCC) algorithm, while ions and neutral species are handled by a fluid model, including a time slicing technique to reduce the computational expenses caused by the responses of various species on different time scales. The code is used to investigate a capacitively coupled COST reference micro atmospheric pressure helium plasma jet with 0.1% oxygen admixture excited by a valley-type tailored voltage waveform with a fixed peak-to-peak voltage of 400 V, and a fundamental frequency of 13.56 MHz. The computational results are compared to experiments based on several sophisticated diagnostics, showing good agreement in the electron impact helium excitation rate, the helium metastable density, and the atomic oxygen density. The spatio-temporal electron heating dynamics, are found to be asymmetrical due to the specific shape of the driving voltage waveform. Tailoring the voltage waveform is shown to enable to control the electron energy probability function (EEPF) in distinct spatio-temporal regions of interest. As a consequence, the generation of reactive neutral species can be enhanced by increasing the number of consecutive harmonics. Based on a simplified two dimensional neutral transport model in the hybrid code, it is demonstrated that the transport between the electrodes, as well as the gas flow have different effects on various neutral species distributions due to the relevant chemical reaction rates for the generation and destruction of species.

Electron heating mode transitions in radio-frequency driven micro atmospheric pressure plasma jets in He/O2: a fluid dynamics approach

“…The number of total reactions is reduced according to the sensitivity analyses [40]. The chemical reactions considered in this work are the same as those listed in [18]. Surface coefficients for neutral species are treated as a loss probability [33,55].…”

“…The control of the production of reactive oxygen and nitrogen species (RONS) within the discharge volume is crucial for these applications. One method is the use of voltage waveform tailoring [12,13], which has been shown the capability of tuning the dynamics of electron energy distributions (EEDs) [14][15][16][17][18]. Typically, the EED deviates from a Maxwellian distribution particularly for high energies even at atmospheric pressure since the energy relaxation length can be larger than length scale of the reduced electric field gradients.…”

Electron heating mode transitions in radio-frequency driven micro atmospheric pressure plasma jets in He/O$_{2}$: A fluid dynamics approach

“…A real hybrid model would be a more effective solution for simulating sophisticated discharges with multiple species more accurately. This has been already shown by the authors elsewhere based on a coupling between a 1d3v (one dimension in displacement, three dimensions in velocity) PIC/MCC model and a 2D simplified fluid model [18]. However, in order to consider the lateral gas flow, a sophisticated hybrid model including 2d3v PIC/MCC algorithm and 2D fluid model would be ultimately needed.…”

“…The control of the production of reactive oxygen and nitrogen species (RONS) within the discharge volume is crucial for these applications. One method is the use of voltage waveform tailoring [12,13], which has been shown the capability of tuning the dynamics of electron energy distributions (EED) [14][15][16][17][18]. Typically, the EED deviates from a Maxwellian distribution particularly for high energies even at atmospheric pressure since the energy relaxation length can be larger than length scale of the reduced electric field gradients.…”

Propagation dynamics and interaction of multiple streamers at and above adjacent dielectric pellets in a packed bed plasma reactor

“…−5 kV was found not be high enough to achieve plasma breakdown in the simulation, while in experiments, a discharge is generated at −2.5 kV by initially increasing the voltage above this value and later decreasing it. The higher voltage may be required as the model cannot capture the kinetic effects as explained for micro atmospheric pressure RF plasma jets [37,38]. A rise-time approximately similar to the corresponding experimental value of 28 ns was used in the modeling for an applied voltage of −8 kV.…”