The paper presents an application of empirical mode decomposition (EMD) for the analysis of intermittent chaotic fluctuations from a glow discharge plasma. Here, the nature of the oscillations changes from an initial relaxation oscillation to a final chaotic oscillatory state via intermittent chaos. The time series data have been decomposed into several intrinsic mode functions (IMFs) using EMD. Furthermore, the estimation of the variance of the IMFs and the correlation of these IMFs with the original time series help us to identify the presence of coherent modes in the fluctuations. Through this analysis, we could clearly observe that initially during the relaxation oscillations the system was dominated by one type of coherent mode, whereas in the final chaotic state, it was dominated by another coherent mode. In the intermediate case, i.e., intermittent chaotic state, both the coherent modes are seen to be present. We have also used rescaled range (R/S) statistical method to identify the coherent modes and corroborate with the results obtained using EMD. The Hilbert Huang spectrum of the fluctuations clearly suggests the intermittent change in the frequency with time.
Intermittent chaos was observed in a glow discharge plasma as the system evolved from regular type of relaxation oscillations (of larger amplitude) to an irregular type of oscillations (of smaller amplitude) as the discharge voltage was increased. Floating potential fluctuations were analyzed by different statistical and spectral methods. Features like a gradual change in the normal variance of the interpeak time intervals, a dip in the skewness, and a hump in the kurtosis with variation in the control parameter have been seen, which are strongly indicative of intermittent behavior in the system. Detailed analysis also suggests that the intrinsic noise level in the experiment increases with the increasing discharge voltage. An attempt has been made to model the experimental observations by a second order nonlinear ordinary differential equation derived from the fluid equations for an unmagnetized plasma. Though the experiment had no external forcing, it was conjectured that the intrinsic noise in the experiment could be playing a vital role in the dynamics of the system. Hence, a constant bias and noise as forcing terms were included in the model. Results from the theoretical model are in close qualitative agreement with the experimental results.
Floating potential fluctuations of a glow discharge plasma are found to exhibit different kinds of mixed mode oscillations. Power spectrum analysis reveals that with change in the nature of the mixed mode oscillation (MMO), there occurs a transfer of power between the different harmonics and subharmonics. The variation in the chaoticity of different types of mmo was observed with the study of Lyapunov exponents. Estimates of correlation dimension and the Hurst exponent suggest that these MMOs are of low dimensional nature with an anti persistent character. Numerical modeling also reflects the experimentally found transitions between the different MMOs.
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