Potential double layers are observed to form as nested cylindrical sheaths that energize charge particles in the absence of any externally applied magnetic field. These visibly glowing nested cylindrical sheaths are named as “Fire Tube” in the present work. Sheaths, in unmagnetized collisionless plasmas, have been observed to be functional in generating energetic charge particles. Two characteristically different plasma sources are compared in terms of the dependence of potential and density profiles on the plasma sheath formations near the source boundary. The sheath structures, complex fire tube formation, and space charge formations demarcate the two sources in terms of complex structure formations and motion of the charge particles. We present here the characteristic study of high pressure collisional boundary sheath formations through systematic experiments carried out during the transition from unmagnetized to magnetized charge particles, in the case of two different plasma sources designed. The cylindrical ambient plasma sheaths are observed to energize the charge particles, in the absence of any external magnetic field. The fire tube formations essentially represent a non-neutral region located radially away from the plasma source boundary, connecting the ion sheath with the electron sheath. The probe diagnostic results suggest a significant role of energetic electrons in the formation of multiple double layer structures in the present operational regime. Generation of nonthermal electrons during the formation of MDL in radio frequency capacitive discharges is subjected to interactions of the plasma with the electrodes as well as the confining wall material.

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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.

Multiple luminous sheath structures develop in the localised plasma formation inside a cylindrical gridded cathode plasma source. These structures gradually expand into the whole vessel and undergo a critical state through self‐organised criticality (SOC) along with pronounced sheath oscillations during the variation of anode potential. The present investigation emphasises the stability properties associated with the oscillations of the sheath potential structures in the cylindrical‐gridded cathode in glow discharge regime through SOC phenomena through non‐linear time series analysis. The non‐linear temporal and spatial analysis of potential structure and dynamics of charged particles are correlated with SOC in cylindrical‐gridded cathode in glow discharge regime through the dynamics of multiple sheath structure formations. The existence of flicker noise and long‐range correlation in the time series suggests the existence of SOC behaviour in the system, the multiple sheath structures evolve through reduction and addition of layers. Cylindrical‐gridded cathode discharge initiation during formations of multiple sheath structures, switching of discharge regimes with anode potential, layer reduction and addition inside the sheath structures through SOC behaviour, renders uniqueness to the present regime of investigation. Self‐organised pattern formations and self‐organised criticality behaviour investigated in the present glow discharge regime using the cylindrical‐gridded cathode source are of prime importance to understand the complex behaviour of plasmas in the field of hollow cathode discharges.