Self-organized criticality: An interplay between stable and turbulent regimes of multiple anodic double layers in glow discharge plasma

Abstract

The role of self-organized criticality (SOC) in the transformation of multiple anodic double layers (MADLs) from the stable to turbulent regime has been investigated experimentally as the system approaches towards critical behavior. The experiment was performed in a modified glow discharge plasma setup, and the initial stable state of MADL comprising three concentric perceptible layers was produced when the drift velocity of electrons towards the anode exceeds the electron thermal velocity (νd ≥ 1.3νte). The macroscopic arrangement of both positive and negative charges in opposite layers of MADL is attributed to the self-organization scenario. Beyond νd ≥ 3νte, MADL begins to collapse and approaches critical and supercritical states through layer reduction which continue till the last remaining layer of the double layer is transformed into a highly unstable radiant anode glow. The avalanche resulting from the collapse of MADL leads to the rise of turbulence in the system. Long-range correlations, a key signature of SOC, have been explored in the turbulent floating potential fluctuations using the rescaled-range analysis technique. The result shows that the existence of the self-similarity regime with self-similarity parameter H varies between 0.55 and 0.91 for time lags longer than the decorrelation time. The power law tail in the rank function, slowly decaying tail of the autocorrelation function, and 1/f behavior of the power spectra of the fluctuations are consistent with the fact that SOC plays a conclusive role in the transformation of MADL from the stable to turbulent regime. Since the existence of SOC gives a measure of complexity in the system, the result provides the condition under which complexity arises in cold plasma.

Formation of multiple anodic fire spots inside an electrostatic cavity

“…The H-exponent is a self-similar parameter that determines the long-term correlation in the recorded time series. [8,10,12,33] Generally, 0.5 < H < 1 indicates the persistency of the signal, H = 0.5 [8] The variation of the H-coefficient with anode potential is shown in Figure 10. The charged particles are reorganized during the SOC behaviour and balance the flux of charged particles inside the anode spots to maintain the quasineutrality.…”

“…[1][2][3][4][5] However, in almost all of these cases, an ambient cathode plasma was produced by filament within a certain gas pressure range, in the absence of a magnetic field as well as in the presence of a magnetic field. [6 -9] Self-organized criticality (SOC) behaviour was investigated earlier during Double Layer (DL) formations in various confinement devices, mostly near the electrodes, [8,10,12] owing to its vital importance in the investigation and understanding of complexities in space plasma and fusion plasmas. [13 -15] The SOC indicates the existence of self-similarity in the discharge states and helps in understanding the fractal dimensions during such a discharge regime.…”

“…The nonlinear analysis of the Hurst exponent and the presence of 1/f power law in the dynamical systems is the identification of the SOC behaviour resulting in the formation and dynamics of multiple potential structures and indicating the complexities of the plasma discharge during the formation of multiple potential structures. [8,12,16,17] The paper also presents a detailed analysis of the identification of coherent modes as well as the distribution of energy among them during the SOC behaviour of the discharge through the application of the Empirical Mode Decomposition (EMD) technique. [21] The statistical technique, Empirical Mode Decomposition (EMD), resolves a signal into its inherent modes and identifies them as intrinsic mode functions (IMFs).…”

Study of self‐organised criticality in a coaxial plasma source with gridded cathode

“…During V A reversal, the expanded glow in regime II remains stable up to ∼536 V denoted by (F) in Figure 2, and for V A < 530 V, the glow discharge re-organises to maintain quasineutrality through localisation of the plasma inside the coaxial plasma source, up to three distinctly visible multiple sheaths with sharp boundaries at the opening of the plasma source, through the addition of layers. [12,26] F I G U R E 3 Images show the complex structure evolution and transformation of discharge during the variation of anode potential at a constant gas pressure of 0. Henceforth, the anode potential V A ∼ 536 V will be termed as the lower critical voltage during the lowering of anode potential.…”

“…During the formations and collapse of such multiple sheath structures, the phase space trajectories suggest significant SOC behaviour in the present discharge regime. [12,26] The power spectrum analysis also reveals the frequency distribution over the entire time series, as the logarithmic plot of the frequency with power spectrum shows the stability of the system while indicating the transition of states. [33] During the layer reduction, the power spectrum analysis corresponding to SOC follows the power-law 1/f β in the logarithmic plot of the frequency with power, where 'f' is the frequency and 'β' is the fractional power of the frequency.…”