Suppression of Plasma Current by Insulator in Atmospheric Pressure Plasma Jet

Plasma is generated by applying a high voltage to electrode wrapped around the quartz tube. A jet-shape plasma is formed by flowing a rare gas inside a tube at atmospheric pressure. At atmospheric pressure, ions follow the flow of neutral gases, thus, the plasma current consists of electrons moving electromagnetic force. The plasma current passing through the quartz tube is suppressed by equipping an insulator to the outside of the quartz tube. Since the dielectric quartz is polarized internally, the plasma in contact with the inner surface of the quartz tube is induced to the positive polarity on the outer surface of the quartz tube. The high voltage applied to the copper electrodes generates electromagnetic induction noise spatially. Electromagnetic induction noise causes electrons in the atmosphere to vibrate, causing the surface of the insulator to become charged with electrons. The charged electrons on the surface of the insulator induce a positive polarity on the inner surface of the quartz tube. Therefore, inside the quartz tube in the radial direction, the polarization directions due to the applied voltage and the plasma are reversed, so that the net polarization strength inside the quartz tube is reduced. The polarization inside the quartz tube changes depending on the balance between the amount of electrons charged on the insulator surface and the amount of plasma charge. When the plasma charge weakens the polarization inside the quartz tube caused by electrons on the insulator surface, the plasma charge is reduced and the electromagnetic force acting on the plasma is suppressed. While when the amount of plasma charge is insufficient to weaken the polarization caused by electrons charging the insulator surface, or when the amount of plasma charge is excessive compared to the amount of electrons charging the insulator surface, the plasma induces electron charging on the insulator surface, thus the electromagnetic force acting on the plasma is suppressed and the plasma current decreases.