Charge-up of Metal Plate Treated by Low-Temperature Atmospheric Pressure Helium Plasma Jet

Low-temperature atmospheric pressure plasmas have been intensively investigated for biomedical applications. Nowadays an application spectrum is very broad including sterilization, wound care, cancer therapy, blood coagulation, and regenerative medicine. In wound care, there are already several clinical studies conducted using the low-temperature atmospheric pressure plasmas. Moreover, the application filed has expanded to agriculture such as food preservation, promotion of seed germination, disease management, and the promotion of growth.<br/>From the low-temperature atmospheric pressure plasmas, there are several agents responsible for biomedical effects including charged particles, reactive nitrogen and oxygen species, UV light, and heat. So far, the biomedical effects by the plasmas are mainly discussed in terms of reactive species. For example, bactericidal property in plasma activated water is well explained by the reactive species and their reaction [1]. Moreover, acetyl and pyruvic acid-like groups generated in plasma-treated Ringer’s lactate solution contributed to the anti-tumor effect [2]. However, charging on surface could also contribute to the biomedical effects. For example, the local charging results in a built-up of strong electric field and cell rupture accordingly. Moreover, the developed electric field can influence on the transport of reactive species in liquid because some reactive species have a charge. In this contribution, we investigated a charge-up on electrically floating metal plate treated by low-temperature atmospheric pressure helium plasma jet.<br/>In this study, an atmospheric pressure helium plasma jet was used. This plasma jet has been developed and tested for blood coagulation. The plasma device has a dielectric barrier discharge plasma source inside and it was driven by applying a high voltage of maximum 6 kV peak-peak at 62 kHz in frequency [3]. Using helium gas of 1 l/min, a plasma flare was ejected from the nozzle (quartz tube of 1.4 mm in diameter) of plasma device. An electrically floating copper plate was treated by the plasma and the capacitance between the plate and ground was 15 pF. The distance between the nozzle of plasma device and cooper electrode was changed between 5 and 25 mm in this experiment. The potential of copper plate was measured by an electrostatic sensor in a non-contact manner. The sensor was placed about 50 mm away from the plasma treatment position. It was confirmed that the use of electrostatic sensor did not disturb the electrical characteristics of plasma.<br/>The measurement of potential on the copper plate showed that the potential could be controlled from positive to negative by changing the distance between the plasma device and the copper plate. When the distance was small, the formed potential on the copper plate was positive. On the other hand, the potential was negative with larger distance. In the presentation, we introduce the potential on the copper plate as a function of the distance between the nozzle of plasma device and the copper plate. The distribution of charged particles in the plasma flare is mentioned and the relation between charging and the distribution of charged particles will be discussed. Moreover, the other charging mechanism including electron emission through thermionic, photoelectric processes, etc. will also be considered.<br/>References: [1] Ikawa et al. Plasma Process. Polym. <b>7</b>(2010)33. [2] Tanaka et al. Sci. Rep. <b>6</b>(2016)36282. [3] Takeda et al. J. Phys. D: Appl. Phys. <b>52</b>(2019)165202.