Ionization fronts in planar dc discharge systems with high-ohmic electrode

Area of Science:

• Plasma Physics
• Nonlinear Dynamics
• Electrical Engineering

Background:

• Electric breakdown in gases is crucial for many applications.
• High-ohmic cathodes in dc discharges support complex current patterns.
• Understanding ionization fronts is key to controlling discharge behavior.

Purpose of the Study:

• To theoretically investigate electric breakdown and ionization fronts in a dc discharge with a high-ohmic cathode.
• To model the discharge dynamics using a reaction-diffusion system.
• To explain the formation and propagation of ionization fronts and associated current phenomena.

Main Methods:

• Adiabatic electron description.
• Two-scale expansion for macroscopic time scales.
• Analysis of a two-component reaction-diffusion system.

Main Results:

• The discharge in the low-current Townsend mode is governed by a reaction-diffusion system.
• Breakdown is an instability of the overvoltage state, triggering a shock-like ionization front.
• The ionization front propagates at a constant speed (approx. 10^4 cm/s) and exhibits monotonic or oscillatory behavior based on cathode resistivity.
• Damping transient oscillations of global current are explained by the reaction-diffusion model.

Conclusions:

• The reaction-diffusion system provides a quantitative description of the discharge on macroscopic time scales.
• The model successfully explains the emergence of ionization fronts and current patterns in this specific discharge configuration.
• The study offers insights into the fundamental physics of electric breakdown and wave propagation in gaseous systems.