Time evolution of atomic nitrogen density in pure-nitrogen-pulsed barrier discharge at sub-atmospheric pressure

Abstract

Ground state atomic nitrogen N([Formula: see text]) was analyzed using two-photon absorption laser-induced fluorescence (TALIF) in sub-atmospheric pressure nitrogen pulsed barrier discharge under needle-to-hemisphere electrode configuration. By reducing the pressure from 90 to 30 kPa, the discharge form transitioned from multiple filaments to a single column, improving the reacting region uniformity. The TALIF measurement revealed that the amount of atomic nitrogen near the needle anode increased over tens of microseconds after the discharge, and this N-production during afterglow was enhanced by reducing the pressure. Reducing the pressure from 90 to 30 kPa extended the half-life period of atomic nitrogen near the anode by 350 [Formula: see text], while maintaining the peak amount of atomic nitrogen. The lifetime extension with the same amount of atomic nitrogen helped improving the chemical activity near the anode. The origin of the N-production during afterglow was not identified as a single factor, but its time constant indicated the contribution of N[Formula: see text] quenched by the ground state atomic nitrogen, along with the quenching of N[Formula: see text], which was previously considered as a major source of afterglow production of the ground state atomic nitrogen. Under 30 kPa, higher discharge energy resulted in faster and larger amount of atomic nitrogen production during afterglow, which indicates the involvement of highly excited particles including metastable atomic nitrogen. In contrast, the decay rate of atomic nitrogen did not depend on the discharge energy. This suggests that the increasing discharge energy broadens the N-productive region while maintaining the local N density.

Concentration measurements of atomic nitrogen in an atmospheric-pressure RF plasma jet using a picosecond TALIF

“…The obtained lifetime values agreed well (within 13%) with their theoretical estimations based on the known quenching rate coefficients [22]. We did not found any significant change of N * lifetime caused by variation of the RF power, which is similar to the observation of Nakagawa et al [47] in a pulsed barrier discharge.…”

“…Finally, the discharge extinguished when 0.7% of N 2 was added to He. Nakagawa et al [47] extended the work of Dvořák et al [18] in nitrogen pulsed barrier discharge under needle-to-hemisphere electrode configuration. In both works [18,47] influence of pressure on the production of atomic nitrogen was studied, and the results indicated that higher pressures lead to increased concentration of atomic nitrogen.…”

“…Nakagawa et al [47] extended the work of Dvořák et al [18] in nitrogen pulsed barrier discharge under needle-to-hemisphere electrode configuration. In both works [18,47] influence of pressure on the production of atomic nitrogen was studied, and the results indicated that higher pressures lead to increased concentration of atomic nitrogen. Niemi et al [34] analyzed the trend of absolute density of atomic nitrogen in radio-frequency (RF) atmospheric-pressure plasma source operated in a helium feed gas with air-like mixtures of N 2 /O 2 (4:1).…”

“…There is a lack of data on Rabi frequency for the used transition, but from the low value of the two-photon absorption cross-section, we estimate that the used laser intensity was sufficiently low to use the rate equation approximation [52]. Therefore, the average density of the atomic nitrogen was calculated by the wellknown method reported in [18,25,47]. Accordingly,…”

“…Considering our findings on atomic nitrogen density to previous studies, we find that our results are within a comparable range. For examples, in the pure-nitrogen-pulsed barrier discharge, [47] and filamentary streamer discharge [18] experiments, the highest reported concentration values of atomic nitrogen were 1.2 • 10 15 cm −3 and 1.4 • 10 15 cm −3 respectively. In the case of the micro-scale APPJ [58] with 0.25% N 2 admixture in helium gas, the maximum density of atomic nitrogen achieved was approximately 1.5 • 10 14 cm −3 .…”