Time-resolved imaging and spectroscopy of atmospheric pressure plasma bullet propagation and RONS production

Abstract

An atmospheric pressure plasma jet visually appears as a continuous plasma, but is actually comprised of a series of fast moving ionization waves, commonly called plasma bullets. Plasma bullets are the visible front of ionization streamers. Studying their spatiotemporal formation and propagation can help understand the plasma dynamics. In this work, the formation and lifetime of a high voltage pulsed dc plasma jet and the subsequent bullets were observed using time-resolved synchronized measurements with an intensified charge-coupled device (ICCD) camera and an ICCD spectrometer. The operating voltage, helium flow rate, and pulse width were varied to observe changes in bullet behavior. The measured velocities of the plasma bullets largely depended on voltage but showed that flow rate can have an effect. The formation of OH and excited N 2 (2+) was measured at the nanosecond timescale. It was seen that the formation of these species begins at the visible bullet, but the peak emission and decay occur ∼50-100 ns after bullet passage, indicating a finite time of reaction, excitation, and emission. Observing the temporal formation of plasma bullets and reactive species provides insight into some of the reactions occurring in the discharge and how to tailor the plasma operating conditions.

Studies on plasma‐activated perilla seed oil: Diagnosis, optimisation, and validation of reactive species

“…Discharge imaging is a useful and intuitive method to analyse plasma evolution in plasma jet [37]. Figure 3 reveals that the CAP jet is composed of plasma bullets with the propagation velocity of about 10 5 m/s, much higher than the gas flow rate (3.18-5.31 m/s), indicating that the propagation of plasma bullets depends on the electric fields rather than the gas flow, which is consistent with the previous reports [38,39]. When the gas flow rate is increased from 0.6 to 1 standard litre per minute (SLM), the plasma bullet propagates from the jet tube earlier, indicating that the increase of gas flow rate is conducive to the advance of discharge.…”

Contrasting the characteristics of atmospheric pressure plasma jets operated with single and double dielectric material: physicochemical characteristics and application to bacterial killing

“…In another commonly used configuration, a single dielectric material separates the HV and the ground electrode [11,16]. Both configurations of the plasma jets have been studied for different applications including biomedicine and water purification [17][18][19][20][21]. Despite the scale of their applications, there is considerable ambiguity as to their relative characteristics and merits for the aforementioned applications, thus making direct comparisons between studies difficult.…”

A 2D steady state analytical model for atmospheric pressure RF plasma jet

“…Despite substantial efforts, characterization of the plasma jet region is felt to be inadequate even today, not only due to its small size, non-equilibrium nature and complexity, but also due to limitations of the diagnostic tools (including their cost) and the difficulties involved in data acquisition and analysis [23,32,[38][39][40]. On the other hand, much can be gleaned about this region from an analytical model of the plasma in the discharge tube.…”

“…It must be pointed out here that the field of RF-based APPJ lacks a detailed and realistic analytical model even for the plasma in the discharge tube and this work attempts to fill the gap in this direction. The model developed is a 2D model for continuous, steady-state plasma, which assumes, as already mentioned earlier, that the frequency of the applied RF power is high enough so that the formation of streamers and plasma bullets (due to periodic quenching of the plasma in each quarter of a cycle) is ruled out [23,39]. In such a model, RF power absorption is assumed to be due to electron-atom collisions.…”