Bulletin of the American Physical Society
76th Annual Gaseous Electronics Conference
Volume 68, Number 9
Monday–Friday, October 9–13, 2023; Michigan League, Ann Arbor, Michigan
Session HR4: Plasma in Liquids
1:30 PM–3:30 PM,
Thursday, October 12, 2023
Room: Michigan League, Michigan
Chair: Ahmad Hamdan, Université de Montréal
Abstract: HR4.00006 : Initiation and propagation mechanisms of underwater streamers*
3:00 PM–3:30 PM
Presenter:
Takehiko Sato
(Tohoku University)
Authors:
Takehiko Sato
(Tohoku University)
Hidemasa Fujita
(Tohoku Univ.)
Ryo Kumagai
(Tohoku Univ.)
Seiji Kanazawa
(Oita Univ.)
Kiyonobu Ohtani
(Tohoku Univ.)
Atsuki Komiya
(Tohoku Univ.)
Tomoki Nakajima
(Tohoku Univ.)
Toshiro Kaneko
(Tohoku University)
The initiation process of the positive streamers visualized by a high-speed camera of 100 Mfps was related to the bubble theory because the streamer inception was observed from the tip of a protrusion on the surface of this bubble cluster. Regarding the secondary steamer propagation with a velocity of 32 km/s, the streak imaging showed that luminescence preceded gas channel generation, suggesting a mechanism of direct ionization in water. In addition, the streak imaging of primary streamer propagation with a velocity of 2.4 km/s revealed intermittent propagation, synchronized with repetitive pulsed currents. Shadowgraph imaging of streamers synchronized with the light emission signal indicated the possibility of direct ionization in water for primary and secondary streamer propagation.
For the propagation processes of the negative streamers, as negative streamers are much smaller and have weaker luminescence compared with the positive streamers, a new visualization optical system was newly developed to detect weak pressure waves using a pair of polarizing plates. The generation of pressure waves was observed at the same time as the pulsed currents accompanied by light emissions detected by a streak camera. Our results indicated that the initiation of the streamer generates pressure waves. Analysis of temporal resolution with nano-second order clarified that the streamer propagates intermittently with the distance of ~20 µm and the interval of ~20 ns, and also the branching phenomenon occurred at different times resulting in the branching streamer propagation in different directions.
*This study was partly supported by the JSPS KAKENHI (Grant No. 24108004, No. JP16H02311), and by a grant from the Collaborative Research Project of the Institute of Fluid Science, Tohoku University.
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