A self-consistent hybrid model of kinetic striations in low-current Argon discharges

TL;DR

This paper presents a self-consistent hybrid kinetic model for understanding standing and moving striations in low-current DC noble gas discharges, incorporating surface diffusion in phase space and detailed plasma chemistry.

Contribution

It introduces a novel kinetic model with surface diffusion in phase space and couples it with ion transport and Poisson equations to simulate striation dynamics.

Findings

Standing striations occur at low currents in Townsend and glow discharges.

Moving striations originate at the anode and propagate towards the cathode at higher currents.

The model reproduces experimental-like s and p striation patterns.

Abstract

A self-consistent hybrid model of standing and moving striations was developed for low-current DC discharges in noble gases. We introduced the concept of surface diffusion in phase space described by a tensor diffusion in the nonlocal Fokker-Planck kinetic equation for electrons in the collisional plasma. Electrons diffuse along surfaces of constant total energy between energy jumps in inelastic collisions with atoms. Numerical solutions of the 1d1u kinetic equation for electrons were obtained by two methods and coupled to ion transport and Poisson solver. We studied the dynamics of striation formation in Townsend and glow discharges in Argon gas at low discharge currents using a two-level excitation-ionization model and a full chemistry model, which includes stepwise and Penning ionization. Standing striations appeared in Townsend and glow discharges at low currents. Moving striations were obtained for glow discharges at currents exceeding a critical value. They originate at the anode and propagate towards the cathode. We have obtained two types of moving striations with the two-level and full chemistry models, which resemble the s and p striations previously observed in the experiments. Simulations indicate that processes in the anode region could control moving striations in the positive column plasma. The developed model helps clarify the nature of standing and moving striations in DC discharges of noble gases at low discharge currents and low gas pressures.