Impact of ion-neutral collisions in fluid models of plasma sheath

In this thesis, the development of an improved one-dimensional self-consistent fluid modeling of argon plasmas in DC discharges, including the sheath regions, is presented. Comparison of the charged species density, electron mean energy, plasma potential and ion velocity profiles with the profiles obtained by other fluid models and the profiles obtained with 1D3V (one dimension in space and three dimension in velocity) Particles-In-Cell simulations were performed. It is shown that for moderate argon pressure (10 \sim 10² Pa), ion collisions with neutral atoms must absolutely be considered in the fluid model to accurately simulate the discharge, especially in the sheath region, and self-consistent calculation of the ion temperature profile is necessary in the whole simulation domain. Indeed, in the cathode sheath where there is large potential fall, the ion temperature can be several orders of magnitude larger than the background gas temperature. It was found that ion-neutral collisions are responsible for a progressive spreading of the ion velocities in the directions perpendicular to the simulation axis in the cathode sheath. The revised fluid model solves the moment equations of order zero, one and two for both electrons and ions. Also, a clear distinction of parallel and perpendicular directions to the applied electric field was observed, thus the assumption of an isotropic temperature was dropped. Instead, the problem was reduced to one dimension in the fluid model to resolve the parallel direction of the discharge. The new fluid model showed much improved agreement with the PIC results, particularly within the cathode sheath. The new model reproduced well the theoretical Paschen's curve for direct-current argon discharges. The lower pressure limit of the current fluid model was also tested, and the observations highlight the necessity of a similar analysis for the electron collisionality.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Physics

Grantor

University of Saskatchewan

Year dc:date.issued

2025

Author dc:creator

• Mun, Jong Hern

Advisors dc:contributor.advisor

• COUËDEL, Lénaïc
• MURAGLIA, Magali
• AGULLO, Olivier

Committee members dc:contributor.committeemember

• STAFFORD, Luc
• HAGELAAR, Gerjan
• PLIHON, Nicolas
• SMOLYAKOV, Andrei
• BOURASSA, Adam
• ARNAS, Cécile
• NEUFELD, Eric

• plasma, direct-current gas discharge plasma, fluid model, ion temperature, ion collisionality

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10388/16934

OAI identifier oai:identifier

oai:harvest.usask.ca:10388/16934