Observation of a comb-shaped filamentary plasma array under subcritical condition in 303-GHz millimetre-wave air discharge

Masafumi Fukunari,Ryuji Shinbayashi,Yoshinori Tatematsu,Shunsuke Tanaka,Yuusuke Yamaguchi,Teruo Saito

doi:10.1038/s41598-019-54333-5

Masafumi Fukunari, Ryuji Shinbayashi + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-54333-5

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Journal: Scientific Reports	Publication Date: Nov 29, 2019
Citations: 20	License type: open-access

Affiliation: University of Fukui

Abstract

Gas breakdown in the millimetre-wave frequency band is an interesting phenomenon in nonlinear dynamics such as self-organized structure formation. We observed the transition between two types of filamentary plasma arrays in air discharge driven by a 303-GHz millimetre wave. Plasma is ignited at a parabolic mirror’s focal point in the overcritical condition. One array parallel to the electric field vector appears with a spacing of λ/4 at the focal point. Filaments then separate into plasma lumps ~10 μs after ignition. At 20 μs, a new comb-shaped array grows in the subcritical condition. Filaments are parallel to the incident beam with spacing of 0.96 λ and elongate towards the incident beam. This comb-shaped array appears only in the electric field plane; bulk plasma with a sharp vertex forms in the magnetic field plane. This array is created by a standing wave structure generated by waves diffracted from the plasma surface. Filamentary plasma array formations can influence the energy absorption by the plasma, which is important for engineering applications such as beamed energy propulsion.

Highlights

Gas breakdown in the millimetre-wave frequency band is an interesting phenomenon in nonlinear dynamics such as self-organized structure formation
Experimental and numerical studies indicate that their structure is determined by the diffusion process of electrons and by the standing wave generated by the incident beam and reflected beam from the ionization front
The dynamic transition of the discharge structure from OC to SC conditions has been observed as a series of images

Summary

Introduction

Gas breakdown in the millimetre-wave frequency band is an interesting phenomenon in nonlinear dynamics such as self-organized structure formation. Experimental and numerical studies indicate that their structure is determined by the diffusion process of electrons and by the standing wave generated by the incident beam and reflected beam from the ionization front. A comb-shaped filamentary plasma array parallel to the incident beam has been predicted using an artificial ionization term with low critical intensity[22].

Results

Conclusion