06_kdowaki_streamer - 484 K. Kadowaki et al.: Space Charge...

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K. Kadowaki et al.: Space Charge Effect for Streamer Initiation and Propagation 1070-9878/06/$20.00 © 2006 IEEE 484 Space Charge Effect for Streamer Initiation and Propagation in Water Subjected to Reciprocal Traveling Wave Voltage Pulse Kazunori Kadowaki, Sakae Nishimoto and Isamu Kitani Ehime University Faculty of Electrical and Electronic Engineering Bunkyo-cho 3, Matsuyama, Ehime, 790-8577, Japan ABSTRACT This paper deals with initiation and propagation processes of streamer discharges in water subjected to high-speed repetitive voltage pulse. The 50%-duty repetitive pulses were produced by the reciprocal traveling wave in a pulse forming cable which was connected with a point-plane electrode gap in a water-cell. Laue plot of time lag distributions for the streamer initiation indicated that the initiation probability during the second pulse application became much higher than that during the first pulse application. We concluded that the change in space charges distribution due to internal field during the rest-time after the first pulse enhanced the streamer initiation probability at the second pulse application. Temporal development in the positive streamers during the repetitive pulse application was observed using a gated image intensifier. When the pulse was relatively high, the streamer discharges started the propagation at the first pulse and then the discharge channel became long step by step at the subsequent pulse applications. It was also found that the periodical emission due to excitation of OH radicals was detected for a long period after the development of the streamer discharge in a spectroscopic measurement. Index Terms Transient propagation, water pollution, delay estimation, space charge, Laue plots, streamer discharges, liquid dielectrics, OH radicals, spectroscopic measurements. 1 INTRODUCTION THERE are many studies on streamer discharges in water and their applications for pollution control and for sterilization [1-6]. It is known that the streamer propagation in water results in UV light emission, shock-wave propagation and the generation of active species, such as OH, O, O 3 and H 2 O 2 . From the viewpoint of the energy efficiency for the water treatment, streamer discharges produced by a short width voltage pulse has a great advantage for low power consumption because the voltage pulse can produce non- equilibrium plasma in which only the electron component has a high kinetic energy. During the last three decades, physical processes of the streamer propagation in water have been studied by many researchers [7-13]. In these studies, only a single rectangle voltage pulse has been used for the tests although the shape of the voltage pulse plays important roles for the streamer propagation.
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06_kdowaki_streamer - 484 K. Kadowaki et al.: Space Charge...

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