No abstract

The dynamic behavior of ionization waves in glow discharge plasma was examined, particularly with regard to periodicity. In a series of experiments, neon plasma was produced by the glow discharge between two electrodes after the glass tube was evacuated to high vacuum. Fluctuations in the light intensity were sampled with a line-scan camera and photodiodes as spatiotemporal signals for data analysis. The largest Lyapunov exponents were calculated from the time series of the experimental samples to quantitatively estimate the complexity of the system. The signal-to-noise ratio (SNR) became saturated as the intensity of the external force applied to the chaotic state was gradually increased because chaotic oscillations in the ionization wave synchronized to the external force. A periodic orbit in the chaos system was emphasized, and the oscillation became coherent as the state SNR reached its maximum value. When the periodicity was emphasized, the oscillation became coherent not only in time but also in space. Periodicity was also observed in system-induced feedback without an external force. Similar results were obtained with an external force and feedback; however, the former caused the chaos system to synchronize with the external force, while the latter yielded periodic oscillations from the chaos-chaos interaction.

Spatiotemporal structures formed in ionization waves are experimentally investigated in this study. A system involving ionization waves in a discharge tube has a few degrees of freedom in time and space. In our experiment, neon plasma is produced in a glass tube by a glow discharge between electrodes after the tube is evacuated to form a high vacuum. Spatiotemporal signals for the analysis are sampled as fluctuations in the light intensity by using a line-scan camera and photodiodes. The largest Lyapunov exponents are calculated from the time-series data sampled from the line-scan camera and photodiodes. Reconnection in the spatiotemporal structure is observed, which is caused by Eckhaus instability. Topological defects in the spatiotemporal structure are observed, which result in the appearance of spatiotemporal chaos; this leads to an order structure when an electric pulse is applied to the system as an external force or when coupled oscillators are synchronized.