Browsing by Author "Slikboer, Elmar"

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    Revealing Plasma-Surface Interaction at Atmospheric Pressure: Imaging of Electric Field and Temperature inside the Targeted Material
    ([London] : Springer Nature, 2020) Slikboer, Elmar; Acharya, Kishor; Sobota, Ana; Garcia-Caurel, Enric; Guaitella, Olivier
    The plasma-surface interaction is studied for a low temperature helium plasma jet generated at atmospheric pressure using Mueller polarimetry on an electro-optic target. The influence of the AC kHz operating frequency is examined by simultaneously obtaining images of the induced electric field and temperature of the target. The technique offers high sensitivity in the determination of the temperature variation on the level of single degrees. Simultaneously, the evolution of the electric field in the target caused by plasma-driven charge accumulation can be measured with the threshold of the order of 105 V/m. Even though a specific electro-optic crystal is used to obtain the results, they are generally applicable to dielectric targets under exposure of a plasma jet when they are of 0.5 mm thickness, have a dielectric constant greater than 4 and are at floating potential. Other techniques to examine the induced electric field in a target do not exist to the best of our knowledge, making this technique unique and necessary. The influence of the AC kHz operating frequency is important because many plasma jet designs used throughout the world operate at different frequency which changes the time between the ionization waves and hence the leftover species densities and stability of the plasma. Results for our jet show a linear operating regime between 20 and 50 kHz where the ionization waves are stable and the temperature increases linearly by 25 K. The charge deposition and induced electric fields do not increase significantly but the surface area does increase due to an extended surface propagation. Additionally, temperature mapping using a 100 μm GaAs probe of the plasma plume area has revealed a mild heat exchange causing a heating of several degrees of the helium core while the surrounding air slightly cools. This peculiarity is also observed without plasma in the gas plume.
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    Towards plasma jet controlled charging of a dielectric target at grounded, biased, and floating potential
    ([London] : Springer Nature, 2022) Slikboer, Elmar; Guaitella, Olivier; Garcia-Caurel, Enrique; Sobota, Ana
    Electric field and surface charge measurements are presented to understand the dynamics in the plasma–surface interaction of a plasma jet and a dielectric surface. The ITO coated backside of the dielectric allowed to impose a DC bias and thus compare the influence of a grounded, biased and floating potential. When imposing a controlled potential at the back of the target, the periodical charging is directly dependent on the pulse length, irrespective of that control potential. This is because the plasma plume is sustained throughout the pulse. When uncontrolled and thus with a floating potential surface, charge accumulation and potential build-up prevents a sustained plasma plume. An imposed DC bias also leads to a continuous surface charge to be present accumulated on the plasma side to counteract the bias. This can lead to much higher electric fields (55 kV/cm) and surface charge (200 nC/cm2) than observed previously. When the plasma jet is turned off, the continuous surface charge decreased to half its value in 25 ms. These results have implications for surface treatment applications.