Experimental and numerical investigation of the transient charging of a dielectric surface exposed to a plasma jet

Abstract

This work investigates the dynamical charging of a surface under exposure of a non-equilibrium plasma jet at atmospheric pressure through a quantitative comparison between modeling and experiments. We show using mono-polar pulses with variable pulse duration and amplitude that the charging time (i.e. the time from impact of the ionization wave till the fall of the high voltage pulse) is a crucial element determining the plasma-surface interaction. This is done through direct measurements of the electric field induced inside the target using the optical diagnostic technique called Mueller polarimetry and comparison with the electric field calculated using a 2D fluid model of the plasma jet interaction with the target in the same conditions as in the experiments. When the charging time is kept relatively short (less than 100 ns), the surface spreading of the discharge and consequent surface charge deposition are limited. When it is relatively long (up to microseconds), the increased surface spreading and charge deposition significantly change the electric field to which the target is exposed during the charging time and when the applied voltage returns to zero.

Revealing Plasma-Surface Interaction at Atmospheric Pressure: Imaging of Electric Field and Temperature inside the Targeted Material

“…Locally, this electric field will be relatively high (15-20 kV/cm) due to charge separation allowing for the propagation of the ionization wave, but this does not mean that a targeted material experiences the same quantitative fields, as is shown here with experienced electric fields of 5 kV/cm. The separated fields caused by either volume or surface charges have been examined in 25,26 . Due to charge deposition and alteration of the propagation dynamics in the vicinity of the dielectric target, the electric field values in the plasma plume cannot easily be extrapolated to determine what targets are experiencing.…”

“…It has a significant advantage over conventional diagnostics where normally quantities are obtained inside the plasma in the gas phase and as such have to be extrapolated to estimate what the targeted materials experience at that instance. In our previous works, a comparison is made with a two dimensional fluid model 25,26 . This validates our technique and electric field results and shows that indeed the electric field in the gas phase and inside a dielectric target are different and should be measured separately.…”

Numerical Study of Jet–Target Interaction: Influence of Dielectric Permittivity on the Electric Field Experienced by the Target

“…1. The geometry taken is the same as in the experiments in Slikboer et al [37]. A dielectric quartz tube with relative permittivity of r = 4 , length 3.3 cm (between z = 1.0 cm and z = 4.3 cm), internal radius r in = 1.25 mm and outer radius r out = 2.0 mm is used.…”

“…r = 4 is the value used in the model in Viegas et al [44] and approximately corresponds to organic polymers, biological tissues and materials such as glass. In Slikboer et al [37] a BSO target of r = 56 has been used in the model, to match the electric field measurements with the same target. We should notice that the numerical description of the plasma-target interaction with this target has been validated through comparisons with experiments in that publication.…”

“…Furthermore, that work has allowed to describe the discharge dynamics and relate it with the electric field distributions. Then, in Slikboer et al [37], quantitative comparisons of temporally and spatially resolved electric field evolutions have been performed, considering the same conditions in experiments and simulations and the BSO target. The simulation results have been averaged over 25 ns and through the target thickness to be compared with experimental measurements with the same temporal and spatial resolution.…”