Anode Plasma Formation at the Initial Stage of a Nanosecond Air Discharge

Parkevich, E. V.; Khirianova, A. I.; Agavonov, A. V.; Ткаченко, С. И.; Mingaleev, A. R.; Shelkovenko, T. A.; Огинов, А. В.; Pikuz, S. A.

doi:10.1134/s1063776118030160

Cited by 21 publications

(19 citation statements)

References 9 publications

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“…These spots were already reported in Ref. [19,24]. To observe the evolution of the plasma during the applied pulse at different pressures, ICCD imaging and OES are performed with a temporal resolution of 480 ps.…”

Section: Methodsmentioning

confidence: 86%

“…In addition, the hydrodynamic effects of the discharge were measured by laser interferometry. Parkevich et al [22][23][24] recently measured the full ionization of nanosecond discharges by laser interferometry. In their conditions [23], they showed that the discharge propagated in the form of more than ten fully ionized filaments of diameter in the range 10-50 μm.…”

Section: Introductionmentioning

confidence: 99%

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Fully ionized nanosecond discharges in air: the thermal spark

Minesi

Stepanyan

Mariotto

et al. 2020

Plasma Sources Sci. Technol.

106

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The formation and decay of the thermal spark generated by a single nanosecond highvoltage pulse between pin electrodes are characterized in this study. The influence of air pressure in the range 50 -1000 mbar is investigated at 300 K. By performing short-gate imaging and Optical Emission Spectroscopy (OES), we find that the thermal sparks exhibit an intense emission from excited electronic states of N + , in contrast with non-thermal sparks for which the emission is dominated by electronic transitions of N2. Spark thermalization consists of the following steps: (i) partial ionization of the plasma channel accompanied by N2 emission, (ii) creation of a fully ionized filament at the cathode characterized by N + emission, (iii) formation of a fully ionized filament at the anode, (iv) propagation of these filaments toward the middle of the interelectrode gap, and (v) merging of the filaments. The formation of the filaments, steps (ii) and (iii), occurs at subnanosecond timescales. The propagation speed of the filaments is on the order of 10 4 m/s during step (iv). For the 1-bar condition, the electron number densities are measured from the Stark broadening of N + and Hα lines, with spatial and temporal resolution. The electron temperature is also determined, from the relative emission intensity of N + excited states, attaining a peak value of 48,000 K. In the post-discharge, the electron number density decays from 4×10 19 to 2×10 18 cm -3 in 100 ns. We show that this decay curve can be interpreted as the isentropic expansion of a plasma in chemical equilibrium. Comparisons with previous experiments from the literature support this conclusion. Expressions for the Van der Waals and resonant broadenings of H, Hβ, and several lines of O, O + , N and, N + are derived in the appendix.

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Section: Methodsmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Fully ionized nanosecond discharges in air: the thermal spark

Minesi

Stepanyan

Mariotto

et al. 2020

Plasma Sources Sci. Technol.

106

View full text Add to dashboard Cite

show abstract

“…This mechanism explains, in our opinion, the fast transition (< 1 ns) from a non-equilibrium to a thermal plasma, as experimentally observed with nanosecond discharges in Refs. [7][8][9][10][11][12][13].…”

Section: Discussionmentioning

confidence: 99%

“…The different states of non-equilibrium NRP plasmas (corona, glow, and spark) have been described by Pai et al [2]. However, other works [7][8][9][10][11][12][13][14] have shown that nanosecond discharges can also produce fully ionized thermal plasmas. This type of nanosecond discharge, called the thermal spark, is in thermal equilibrium [7] and differs from the NRP spark described by Pai et al [2].…”

Section: Introductionmentioning

confidence: 96%

The role of excited electronic states in ambient air ionization by a nanosecond discharge

Minesi

Mariotto

Pannier

et al. 2021

Plasma Sources Sci. Technol.

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The mechanism of air ionization by a single nanosecond discharge under atmospheric conditions is studied using numerical simulations. The plasma kinetics are solved with ZDPlasKin and the electron energy distribution function is calculated with BOLSIG+. The model includes the excited electronic states of O and N atoms, which are shown to play the main role in plasma ionization for ne > 10 16 cm -3 .For electric fields typical in nanosecond discharges, a non-equilibrium plasma (Te > Tgas) is formed at ambient conditions and remains partially ionized for about 12 nanoseconds (ne < 10 16 cm -3 ). Then, the discharge abruptly reaches full ionization (ne ≈ 10 19 cm -3 ) and thermalization (Te = Tgas ≈ 3 eV) in less than half a nanosecond, as also encountered in experimental studies. This fast ionization process is explained by the electron impact ionization of atomic excited states whereas the fast thermalization is induced by the elastic electron-ion collisions.

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“…Recently, the study of these discharges at ambient conditions has shown that NRP discharges can also be fully ionized. In [12,13], Parkevitch et al showed by laser interferometry that approximately one nanosecond after a 25-kV voltage rise, a fully-ionized plasma is formed near the cathode surface in a pin-to-plane configuration. Moreover, they observed the formation of "clots" of dense plasma with electron number densities greater than 10 20 cm -3 .…”

Section: Introductionmentioning

confidence: 99%