Experimental and computational investigations of electron dynamics in micro atmospheric pressure radio-frequency plasma jets operated in He/N₂ mixtures

Abstract

The electron power absorption dynamics in radio frequency driven micro atmospheric pressure capacitive plasma jets are studied based on experimental phase resolved optical emission spectroscopy and the computational particle in cell simulations with Monte Carlo treatment of collisions. The jet is operated at 13.56 MHz in He with different admixture concentrations of N 2 and at several driving voltage amplitudes. We find the spatio-temporal dynamics of the light emission of the plasma at various wavelengths to be markedly different. This is understood by revealing the population dynamics of the upper levels of selected emission lines/bands based on comparisons between experimental and simulation results. The populations of these excited states are sensitive to different parts of the electron energy distribution function and to contributions from other excited states. Mode transitions of the electron power absorption dynamics from the Ωto the Penning-mode are found to be induced by changing the N 2 admixture concentration and the driving voltage amplitude. Our numerical simulations reveal details of this mode transition and provide novel insights into the operation details of the Penning-mode. The characteristic excitation/emission maximum at the time of maximum sheath voltage at each electrode is found to be based on two mechanisms: (i) a direct channel, i.e. excitation/emission caused by electrons generated by Penning ionization inside the sheaths and (ii) an indirect channel, i.e. secondary electrons emitted from the electrode due to the impact of positive ions generated by Penning ionization at the electrodes.

Effects of excitation voltage pulse shape on the characteristics of atmospheric-pressure nanosecond discharges

“…This significant difference indicates that most likely the initial charge density is lower in the experiments than our n 0 value, as the plasma density and the peak current sensitively depend on the initial charge density, as it was seen, e.g., in [22]. Despite of this discrepancy in the peak current value, we trust that our code has a predictive ability, as essentially the same code has been used for the description of radiofrequency driven atmospheric pressure microplasma jets, and an excellent agreement was found between the experimental and computed characteristics of these plasma sources [57,58]. Finally we note that while throughout our studies we considered conducting electrodes, the case of dielectric electrodes can also be addressed by our simulation code.…”

Atmospheric pressure dual RF–LF frequency discharge: transition from α to α – γ -mode

“…Bischoff et al [18] studied the modification of the electron power absorption dynamics induced by changing the driving voltage amplitude and the N2 concentration in atmospheric pressure plasma jets operated at 13.56 MHz in He/N2 Penning mixture. Their experiments are based on phase resolved optical emission spectroscopy and their simulations are performed with a Particle In Cell (PIC) code including Monte Carlo treatment of collision processes (PIC MCC).…”

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.…”