Low-frequency one-electrode discharge in long tubes at low gas pressure

TL;DR

This study investigates a novel low-frequency, one-electrode capacitive discharge in long tubes filled with neon or argon at low pressure, revealing unique plasma behaviors and wave propagation mechanisms not seen in RF discharges.

Contribution

It introduces and characterizes the one-electrode discharge (OED) phenomenon, including its plasma generation mechanism, wave dynamics, and striation formation, which were not previously described.

Findings

Discovered low-frequency OED with unique plasma patterns.

Identified ionization waves as key to plasma formation.

Proposed a kinematic model for wave propagation and plasma parameters.

Abstract

The specific form of one electrode capacitive discharge was studied in long tubes filled with high purity neon or argon at pressure 1-4 Torr. The main feature of the discharge is the low rate (less than 10 kHz) of the voltage pulses of given polarity which are applied to only one electrode of the tube, while another one remains free or missing. This type of the discharge was named one-electrode discharge (OED), and seems not to be described in previous studies. The discharge is observed as a glowing plasma column which occupies either entire tube or its part dependent on actual voltage amplitude and on its rate. Current-volt characteristics, ignition thresholds and the OED length changing patterns demonstrate features unknown for RF discharges. It was found that the plasma generation mechanism in OED consists in formation and traveling of the set of ionization waves (IW). It was shown that the wave motion is characterized by a pronounced attenuation the patterns of which were investigated by the time-position diagrams method. The attenuation specifies the length of the occupied plasma area as well as other OED parameters. Kinematic model of the wave propagation is proposed. This model allows to estimate the electric field in different OED points as well as average electron concentration via the current measurements; the typical values of the above parameters are $5 V/cm$ and $10^9-10^{10}$ $cm^{-3}$. It was shown that nonhomogeneous electric field behind the IW front creates the conditions for appearance of plasma channel striations observed in the experiment. The stationary striations found in neon are more distinctive for negative polarity OED. It was shown that ionization-drift mechanism with account of metastable states existence in plasma seems to be much adequate for the OED striation description.