Effects of humidity on the dynamics and electron recombination of a pin-to-pin discharge in He + H₂O at atmospheric pressure

Abstract

Control of the plasma chemistry is essential for the effectiveness of atmospheric pressure plasmas in many applications. For this, the effects of the humidity of the feed gas on the discharge chemistry need to be considered. Detailed studies are scarce and many of them are dominated by surface interactions, obscuring any volume effects. Here, a negative nanosecond pulsed discharge is generated in a pin-pin 3 mm gap geometry in He+H2O that enables the study of volume kinetics due to minimal surface area. The effect of humidity on the discharge development, electric field and electron density is investigated through experiments and modelling. It is found that the presence of water vapour affects both the electron density at the start of the pulse (remaining from the previous pulse) and the ionisation rates during the ignition phase, leading to a complex dependence of the discharge development speed depending on the water concentration. The electron decay is studied using the 0D global kinetics model GlobalKin. The dominant reactions responsible for the electron decay depending on the concentration of water vapour are determined by comparing experimental and simulated results and these reactions are grouped in simplified kinetic models. It is found that with water concentrations increasing from 0 to 2500 ppm, the complexity of the dominant reactions increases with in particular O2 +, H2O3 + and water clusters becoming important for high water concentrations. This work also provides experimental data for validation of kinetic models of plasmas in controlled environments.

Plasma‐enhanced evaporation and its impact on plasma properties and gaseous chemistry in a pin‐to‐water pulsed discharge

“…The process of net electron attachment by water vapor is also responsible for the observed low n e in the solution surface region according to the modeling simulation of an atmospheric‐pressure He + H 2 O plasma [ 53 ] . The time‐decay behaviors of n e are in accordance with that observed by Verreycken et al [ 49 ] and Brisset et al [ 56 ] in a positive and negative nanosecond pulsed He‐H 2 O discharge. The peak n e is always appearing in the discharge central core, as illustrated in Figure 7b.…”

“…These fast depletion processes, including following important reactions R1-R5, dramatically accelerate the drop in the amount of electrons particularly at the solution surface, compared to that at the other two discharge areas: The process of net electron attachment by water vapor is also responsible for the observed low n e in the solution surface region according to the modeling simulation of an atmospheric-pressure He + H 2 O plasma [53] . The time-decay behaviors of n e are in accordance with that observed by Verreycken et al [49] and Brisset et al [56] in a positive and negative nanosecond pulsed He-H 2 O discharge. The peak n e is always appearing in the discharge central core, as illustrated in Figure 7b.…”

“…The mechanism behind n e reduction in the solution surface is supposed to be as a result of the enhanced process of electron-ion recombination [52,54] . Water cluster ions such as H 2 O 3 + and H 3 O + (H 2 O) n are formed abundantly under a high vapor population condition [55] . These cluster ions quickly lose electrons through the dissociative recombination process at an extremely high rate coefficient of an order of 10 −5 -10 −8 cm 3 s −1 [52,53] .…”

Evolutions of streamer dynamics and discharge instabilities under repetitive pulses in humid air

“…The streamer discharge is susceptible to environmental conditions (humidity, gas flow, etc) in open air [10,11]. The gas humidity, either from the water vapor concentration in the surrounding air [12,13] or intentionally supplemented in the gas inlet [14,15], is an important factor for the plasma chemistry [16,17]. On the other hand, streamer discharge evolutions under high-frequency repetitive pulses are more complicated than the conventional double-pulse test [18][19][20], e.g.…”

The spatial density distribution of H2O2 in the effluent of the COST-Jet and the kINPen-sci operated with a humidified helium feed gas

“…Their versatility has allowed their application in medicine, materials processing, green industry and agriculture [1][2][3][4][5][6][7]. When operated with a helium feed gas containing small admixtures of water vapour, CAPJs can generate reactive oxygen and nitrogen species (RONS) in appreciable quantities [8][9][10]. The effluent region of CAPJs contains a complex mixture of these RONS, making these devices desirable for biomedical applications such as microbial sterilisation, cancer therapy, and the treatment of chronic wounds [11][12][13].…”