Temporal evolution of the relative vibrational population of N2 (C³∏_u) and optical emission spectra of atmospheric pressure plasma jets in He mixtures

Abstract

In this study, spatial-temporal resolved optical emission spectroscopy and electrical characteristics are employed to study the dynamic evolution of molecules, vibrational distributions, reactive species, and streamer head speed in the generation and propagation of atmospheric pressure plasma jets (APPJs). The images of discharge, waveforms of pulse peak voltage and discharge current, and spatial-temporal emission spectra of N 2 (C 3 Π u → B 3 Π g , 380.5 nm), N + 2 (B 2 Σ + u → X 2 Σ + u , 391.4 nm) and He (3s 3 S → 2p 3 P, 706.5 nm) are recorded, the relative vibration population of N 2 (C 3 Π u ) and the key dynamic process of each discharge pulse are discussed. The effects of pulse peak voltage on emission intensity, vibration population of N 2 (C 3 Π u ) and APPJ speed are also investigated. The results show that the streamer head speed is about 10 5 m s −1 under the pulse peak voltage of 5-9 kV, and both the streamer head speed and emission intensities increase with pulse peak voltage. The emission intensities of N 2 (C 3 Π u → B 3 Π g , 380.5 nm) rise for about 10 ns but fall for several tens of nanoseconds. During the plasma generation process, the direct electron impact process is dominant in generating electronic, vibrationally and rotationally excited N 2 . Several tens of nanoseconds after the generation, spontaneous emission, quenched by N 2 and O 2 dominate the decay process. While the step excitation and Penning ionization extend the duration time of emission intensity. It is also found that the ratio of N 2 (C, υ = 1)/N 2 (C, υ = 0) is at high level within 1µs. The evolution of the ratio is dominated by the direct electron impact in the initial time, and is then possibly influenced by the vibrational relaxation process and downward vibrational-vibrational energy transmission process.

Mode transition and plasma characteristics of nanosecond pulse gas–liquid discharge: Effect of grounding configuration

“…For the spectra of N 2 (C 3 Π u → B 3 Π g ) and N (3 p 4 S o → 3 s 4 P, 746 nm), the excited N 2 (C 3 Π u ) and N (3 p 4 S o ) are mainly generated via the electron‐impact processes. According to the previous studies, when the excited species are generated from the ground state via the electron‐impact processes, their spectral intensities reflect the mean electron energy and density. Therefore, the higher emission intensities of N 2 (C 3 Π u → B 3 Π g ) and N (3 p 4 S o → 3 s 4 P, 746 nm) in the direct grounding discharge indicate that the mean electron energy and density are higher in the direct grounding discharge.…”

“…The relation between the number density of N 2 (C) and the vibrational temperature is given as follows: where N 0 and N 1 are the number density of N 2 (C) at vibrational levels 0 and 1, respectively, E 0 and E 1 are the energy of N 2 (C) at vibrational levels 0 and 1, and k is the Boltzmann constant. The ratio N 0 / N 1 in Equation can be expressed as the ratio of the intensity of N 2 (C 3 Π u → B 3 Π g , 0–2) and N 2 (C 3 Π u → B 3 Π g , 1–3): where I 0 and I 1 are the intensities of N 2 (C 3 Π u → B 3 Π g , 0–2) and N 2 (C 3 Π u → B 3 Π g , 1–3), respectively, v 0 and v 1 are wavenumbers of 380.5 and 375.5 nm, respectively, and q 1 and q 2 are the Franck–Condon factors. According to Equations and , we can conclude that the vibrational temperature is proportional to the ratio of the emission intensities of N 2 (C 3 Π u → B 3 Π g , 0–2) and N 2 (C 3 Π u → B 3 Π g , 1–3).…”

Numerical analysis of nitrogen fixation by nanosecond pulse plasma

“…Nanosecond pulse discharge can provide a lower gas temperature compared with alternate current dielectric barrier discharge (AC DBD) [20]. By adjusting the pulse amplitude, rise time, pulse frequency, and duty cycle, it is expected that the electron temperature, vibrational temperature, and rotational temperature can be efficiently controlled, thus optimizing the efficiency of NO x production [21][22][23]. However, the discharge dynamics at the nanosecond and the subnanosecond timescale are still unclear.…”

Enhancing the adsorption property of macroporous XAD‐2 resin by nanosecond‐pulsed discharge plasma modification

“…Nowadays, nonthermal plasma (NTP) has been regarded as a highly efficient method in many fields [ 17‐25 ] with the characteristics of rich active species, high electron temperature, low gas temperature, [ 26‐28 ] and without chemical wastes. [ 29‐31 ] Additionally, plasma acts only on the sorbent surface of the nanometer scale without damaging the matrix properties of the sorbent.…”