Interactions between ionization waves and potential structure formed at a constriction of the dc He positive column

Abstract

The potential structure formed at a sharp change in diameter of a diffusion-controlled positive column of a low-pressure and low-current dc He glow discharge has been experimentally investigated in relation to either externally or self-excited ionization waves. A strong electric field evolved on a typical distance of 1 cm in front of the constriction to provide the continuity of discharge current through it, when the constricted part of the plasma column is on the anode side. The electron energy distribution function is not in equilibrium with the field, showing the formation of a fast electron group that is quickly dumped out towards the anode because of the inelastic processes and the radial loss. Either an externally or a self-excited ionization wave disturbs the potential structure, by periodically weakening and strengthening it. As a result, large fluctuations of the local axial electric field in the structure occur and, related to them, fluctuations of the discharge voltage and current are yielded, which make the external discharge circuit a positive feedback loop for the ionization waves.

Self-Consistent Analysis of the Spatial Relaxation of a Disturbed Neon Glow Discharge

“…In the downstream region, a spatiotemporal evolution occurs which is similar to that observed in ionization waves. (1,43) The movement of the spatial relaxation structure in cathode direction corresponds to the negative phase velocity typical of ionization waves. A similar spatiotemporal evolution is found when analysing other macroscopic quantities, such as the electric field strength and the electron density.…”

“…While determining this boundary value, the undisturbed ambipolar loss frequency ν pc r is adjusted in such a way that the particle loss n e ν pc compensates for the total ionization, i.e., that the electron particle balance of the positive column is fulfilled. At the anode position, the partial absorption of electrons is characterized by the relationf 1 …”

“…Similar local disturbances may be caused also by constrictions, grids or geometrical changes of the discharge tube. Some papers can be found in the literature (1,2) which report on experimental investigations of the response of glow discharge plasmas on constrictions of the discharge tube.…”

Current-Free Electric Double Layer in a Small Collisional Plasma Thruster Nozzle Simulation

“…Although double layers have been mostly studied for collisionless plasmas, they also appear in collisional plasma (both current-carrying and current-free); examples are the current carrying DL in the cathode region of DC (direct current) discharges with two field reversals in the negative glow and Faraday dark space [37] and in the anode region of DC discharges [38]; the positive column of DC discharges in a constricted tube shows the formation of a DL often associated with the appearance of standing striations near the tube constriction [39,40]. The DL is also found in hollow cathode collisional discharges in which the anode is placed in a separate vacuum vessel communicating with the discharge chamber through an orifice [41].…”

Two-dimensional positive column structure in a discharge tube with radius discontinuity

“…10,11 Formation of the spatially periodical structures in low-pressure discharges behind any perturbation of positive column is of great interest itself. [12][13][14][15] At the present time, the multi-dimensional simulations of glow discharges based on ether the particle-in-cell technique or the moments approach. Particle-in-cell method requires large computational resources and is applicable for discharges with relatively simple structures.…”