Guided plasma jets directed onto wet surfaces: angular dependence and control

Abstract

The optimal use of atmospheric pressure plasma jets (APPJs) for treatment of surfaces—inorganic, organic and liquid—depends on being able to control the flow of plasma-generated reactive species onto the surface. The typical APPJ is a rare gas mixture (RGM) flowed through a tube to which voltage is applied, producing an RGM plasma plume that extends into the ambient air. The RGM plasma plume is guided by a surrounding shroud of air due to the higher electric field required for an ionization wave (IW) to propagate into the air. The mixing of the ambient air with the RGM plasma plume then determines the production of reactive oxygen and nitrogen species (RONS). The APPJ is usually oriented perpendicular to the surface being treated. However, the angle of the APPJ with respect to the surface may be a method to control the production of reactive species to the surface due to the change in APPJ propagation properties and the resulting gas dynamics. In this paper, we discuss results from computational and experimental investigations addressing two points—propagation of IWs in APPJs with and without a guiding gas shroud as a function of angle of the APPJ with respect to the surface; and the use of this angle to control plasma activation of thin water layers. We found that APPJs propagating out of the plasma tube into a same-gas environment lack any of the directional properties of shroud-guided jets, and largely follow electric field lines as the angle of the plasma tube is changed. Guided APPJs propagate coaxially with the tube as the angle is changed, and turn perpendicularly towards the surface only a few mm above the surface. The angle of the APPJ produces different gas dynamic distributions, which enable some degree of control over the content of RONS transferred to thin water layers.

Interaction of atmospheric pressure helium plasma jet with tilted dielectric target: split and deviation of ionization waves

“…The split can be observed with ε r ⩾ 9, and the split is more pronounced as ε r increases from 9 to 56. The increase in ε r leads to an increase in the electric field between the IW and surface, which has been confirmed through the numerical works [22,39]. The enhanced field led to the split of IW.…”

“…When the IW ejects from the nozzle with small α, the IW rapidly split towards the surface at a few mm above the surface. Previous studies have shown that the gas flow field can be affected by the angle of the gas injection [16,22], the helium flow preferentially flows along the surface in the direction of the angled jet. This can result in changes in the propagation of the IW and thus the deviation value is increased.…”

“…Several studies suggested that the relative angle of the APPJ to the target could be used as a control method, for example, to increase the treatment surface area of the target or increase the activity of the plasma activated water [22]. So far, there has been little discussion about the interaction of APPJs with a tilted target.…”

“…The results show that the electric field distribution shape of the target surface discharge is mainly driven by the gas flow rate. Parsey et al [22] suggested that the IW propagates coaxially with the tube after exiting the tube, but eventually IW impacts the target in a direction perpendicular to the surface. Babaeva et al [32] reported the deviation of the IW strikes point on the target from the tube axis, and their results show that the deviation depends on relative permittivity (ε r ) of the dielectric target.…”

Discharge aspects of a snake‐like plasma plume generated by an atmospheric pressure plasma jet with variable argon flow rate

“…Without the restrictions imposed by vacuum systems, atmospheric pressure plasma jets can generate a plasma generally extending a few centimeters from the end of the device. [1,2] The produced plasma in air ambient is also called a plasma plume, [3][4][5][6] in which there are abundant active species. [7] Due to its flexibility and low cost, plasma jet has become a promising tool for the applications in biomedicine, [8,9] material synthesis, [10][11][12] surface modification, [13][14][15] light source, [16] and water purification.…”