Abstract
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.
Highlights
Www.nature.com/scientificreports birefringent pattern was subtracted to obtain the electric field results
Recent numerical work[22] has shown that the experienced electric field inside targets of 0.5 mm thickness at floating potential are similar when the dielectric constant is higher than 4. This means that the reported electric field values and patterns in this work could be comparable to the electric field which is experienced inside e.g. a thin liquid layer, biological tissues, and polymers that are 0.5 mm when they are treated by a helium plasma jet and they are not grounded
Mueller polarimetry is applied to examine the plasma surface interactions in terms of the electric field which is induced inside a target and the temperature pattern that is formed
Summary
Www.nature.com/scientificreports birefringent pattern was subtracted to obtain the electric field results. In the method section the calibration procedure is explained to show how the temperature spatial profile is obtained together with the induced electric field profile This offers a unique diagnostic to investigate the plasma surface interaction. A comparison is made with a two dimensional fluid model[25,26] This validates our technique and electric field results and shows that the electric field in the gas phase and inside a dielectric target are different and should be measured separately. When the operating AC frequency changes, the stability of the ionization waves can alter due to a change in left-over species densities The effect this has on the targeted surface in terms of plasma surface propagation, charge deposition (an induce electric field) and temperature of the sample are reported in this work. The effect this has on the surface interaction is unknown and makes this work important
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
