Propagation of plasma diffusion waves in various plasma discharge columns

Abstract

Summary form only given. The plasma bullet has been explained with the model of streamer propagation in many reports. The streamer theory of ionization wave for plasma plume/bullet might not be enough for proper explanation. The streamer discharge is represented in general to be the random channeling behavior in a wide open space where the discharge path is not restricted. For instances, the discharge of transient state or quasi-steady state must be a streamer discharge in the atmospheric discharge with a sharp needle electrode or with a plane electrode like a dielectric barrier discharge (DBD). However, the plasma jet seems to be a steady state when the discharge path is defined by the glass tube through which the discharge gas is blowing. Therefore, the discharge of plasma jet accompanied with the glass tube seems not to be explained only with the streamer discharge but it must be a normal glow, since the discharge of plasma jet is guided by the flow of inert gas as well as by the discharge route of glass tube or other structures. In this study the electrostatic plasma diffusion waves driven by a plasma density gradient are described to verify the propagation of light signals observed in the discharge experiments such as long discharge tubes, plasma jets, and plasma display panels. Plasma diffusion waves, electron waves and ion waves, propagate together with the group velocity of the wave-packet as u <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g≈</sub> c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /u <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> , with the acoustic velocity c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and the plasma diffusion velocity u <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> . The propagation phenomena are explained in terms of the plasma density gradient associated with discharge parameters such as the plasma scale, the plasma current, and the electric field strength. The evidence of plasma diffusion wave is shown in the observation results of optical signals providing the information of plasma behavior in the atmospheric plasma jet. In a plasma column between a high-voltage electrode and the virtual ground of infinite open air, the velocity is varied at each area as it is about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> m/s inside the glass tube, it becomes fast as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> m/s at the plasma plume exiting the glass tube, and it is slow down to the open air. If the variation of optical intensity corresponds to the plasma density, the propagation velocity could be understood with the density gradient of the plasma. In the optical signals observed in the plasma jets, two types of waves are analyzed. One is a traveling wave along the forward direction of plasma density gradient from high voltage side to the ground electrode. The other is a backward wave from the backward direction of plasma density gradient and a reflecting wave from the ground electrode.