Self-organization of multiple anodic double layers in magnetized plasma

Abstract

We report on the self-organization of multiple double layers (MDLs) and self-organized criticality (SOC) behavior through subsequent layer reduction process around the anode during DC glow discharge in a linear cylindrical vacuum vessel. The present study provides an insight into the characteristic features of self-organized MDLs around the anode itself and the effect of an external magnetic field during its evolution. The MDL formations around the anode initiate through an abrupt jump in the floating potential, ion saturation, and discharge current signals, which suggests an associated sheath—plasma instability of the system. The frequency spectrum of the floating potential exhibits mixed mode oscillations, which later disappears on applying an external magnetic field. The comparative results reveal the complex nature of a simple glow discharge through repeated coupling and decoupling of MDL dynamics during layer reduction process in the presence of an external magnetic field in cusp configuration, while the discharge turns largely oscillatory in the presence of an external magnetic field in mirror configuration. Existence of the SOC behavior in the system is further investigated through nonlinear dynamical analysis of the floating potential fluctuations. The present study on self-organization phenomena in a glow discharge plasma is important for applications regarding utilization or mitigation of self-organization. Self-organized patterns are often formed during plasma interaction with the liquid surface, which play a vital role in diverse applications of plasmas in nanomaterial synthesis and medicine.

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

“…Such multiple sheath formations with progressive anode potential (V A ) through re‐organisation of the multiple sheaths essentially suggest SOC behaviour of discharge, confirmed later through the nonlinear dynamic analysis of time series of discharge current fluctuations in section III‐B. [ 12,24,25 ] A steep rise in the discharge current at V A ∼ 525 V, along with the distinct visual change in the discharge characteristics, indicates a distinctly different discharge mode denoted by (E) in the I‐V A plot in Figure 2. Figure 3d depicts the resulting expansion of plasma inside the whole vessel.…”

“…Figure 3c depicts the visual glow of the last transformation near the anode. With progressive anode potential (A–D in Figure 2), the shape of the multiple sheath formation changes through re‐organisation of the layers, [ 12 ] as clearly visible in Figure 3a–c. Such multiple sheath formations with progressive anode potential (V A ) through re‐organisation of the multiple sheaths essentially suggest SOC behaviour of discharge, confirmed later through the nonlinear dynamic analysis of time series of discharge current fluctuations in section III‐B.…”

“…Subsequently, the localised glow reduces to single sheath structure formation around the anode through harmonic generation, as shown in Figure 3c. On increasing V A above the critical voltage (V A > 525 V), transition in the reconstructed phase space occurs along with a steep increase in the discharge current, whilst the discharge expands into the whole vessel releasing the trapped charged particles, [ 12 ] as shown in Figure 7e. The discharge passes through the critical stage with excursion in the reconstructed phase space, shown in Figure 7e.…”

“…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 ]…”

“…[11] Moreover, the discharge mode transitions occur through the re-organisation of charged particles during the present study that undergoes charged layer reduction and layer addition through self-organisation in the glow discharge regime with progressive anode potential. [12,13] The locally sustained multiple sheath structure formations gradually transit to a critical state of equilibrium on changing the anode potential. Interestingly, the present experiments were carried out in the operational regime of 0.1 torr.cm < pressure (P) × inner diameter (d) of cathode <10 torr.cm in the glow discharge regime resembles largely with some of the hollow cathode discharge operations, [8,11,14] but out of range compared to some of the hollow cathode experimental regime of 0.750 Torr.…”