Plasma action on helium flow in cold atmospheric pressure plasma jet experiments

Abstract

In this work, helium flow modifications, visualized by schlieren imaging, induced by the plasma generated in a plasma jet have been studied in conditions used for biomedical treatments (jet being directed downwards with a low helium flow rate). It has been shown that the plasma action can shift up to few centimeters downstream the effects of buoyancy, which allows to the helium flow to reach a target below in conditions for which it is not the case when the plasma is off. This study reveals the critical role of large and long lifetime negative ions during repetitive operations in the kHz regime, inducing strong modifications in the gas propagation. The cumulative added streamwise momentum transferred to ambient air surrounding molecules resulting from a series of applied voltage pulses induces a gradual built up of a helium channel on tens of millisecond timescale. In some conditions, a remarkable stable cylindrical helium channel can be generated to the target with plasma supplied by negative polarity voltage pulses whereas a disturbed flow results from positive polarity operation. This has a direct effect on air penetration in the helium channel and then on the reactive species production over the target which is of great importance for biomedical applications. It has also been shown that with an appropriate combination of negative and positive polarity pulses, it is possible to benefit from both polarity features in order to optimize the plasma plume propagation and plasma delivery to a target.

Ar(1s5) absolute radial densities in a ns‐pulsed argon plasma jet impinging on dielectric targets at floating potential – plasma action on organic molecules

“…On the contrary, lower τ values were measured for Q = 0.3 l min −1 at z > 4 mm and −0.2 ≤ y ≤ 0.2 mm, and for Q = 0.4 l min −1 at extreme y coordinates. Besides the role of the dielectric target, a critical interplay between the argon jet and the ambient air molecules takes place at these positions . As so, the Ar(1s 5 ) is further quenched through collisions with H 2 O and N 2 /O 2 , resulting in a steep decrease of its effective lifetime.…”

“…The difference in the obtained for the two targets could be due to their different relative permittivity, which is almost the double in the case of the alumina. In fact, the relative permittivity of the material of the surface being impinged by the APPJ has a significant effect on the distribution of the electric field and, thus, on the dynamics of the discharge, and, consequently, on the production of charged and reactive species such as the argon metastables . A clearer overview of the mechanisms inducing the modification of the electric field distribution could be achieved through a numerical model describing the dynamic system APPJ‐target.…”

“…APPJs can be obtained through the excitation/ionization of a noble gas (usually argon or helium) by means of rf, kHz‐sinusoidal and ‐pulsed high voltages (HV) . Besides, they exhibit interesting properties for applications in biomedicine, agriculture, and interactions with inert targets . In the latter applications, the plasma impinges on different liquid and solid surfaces.…”

On the development of a deployable cold plasma endoscope

“…For the utilized inner diameter of 0.4 mm and He gas flow rate of 300 sccm, a gas velocity of about 40 ms −1 is obtained. This velocity is by a factor of 60 larger than the gas velocity of 0.66 ms −1 reported by Darny et al Thus, electro‐hydrodynamic forces interact with the gas flow but are not capable of altering the flow regime within small sample distances.…”

“…Another plasma operation aspect to consider is the interaction of neutral He feed gas with the generated plasma. From thorough investigations by Robert et al and Darny et al, it is known that strong modifications in the gas propagation appear for kHz‐driven cold atmospheric‐pressure He plasma jets . This can have a severe impact when treating biological samples, since the plasma treatment and the pure gas control might be completely different.…”