Experimental and modeling study of warm plasmas and their applications

Shailesh Pradeep Gangoli

doi:10.17918/etd-1864

Conventionally, plasmas are classified into two main types - 'thermal' or 'equilibrium' plasmas and 'non-thermal' or 'non-equilibrium' plasmas. Based on their properties, they are applied for relevant applications such as, thermal plasma for metal spray coatings (requires high temperature) and non-thermal plasma for surface modification of materials (requires high selectivity). However, there exists another group of plasmas that cannot clearly be classified into one of the above two categories - we refer to them as 'warm plasmas'. Warm plasmas operate at moderate power densities (tens of W · cm⁻¹), intermediate gas temperature (T[g] ~ 1500 - 4000 K) and electron density (ne/n ~ 10⁻⁶ - 10⁻³), non-equilibrium electron temperature (T[e] > T[g]). This makes warm plasmas very interesting for applications where both non-equilibrium selectivity and gas temperature simultaneously contribute to the enhancement of the process. The current thesis deals with two specific applications of warm plasmas pursued at the Drexel Plasma Institute. The first part of the thesis deals with the gliding arc (GA) discharge. It is a popular choice of (warm) plasma for use in energy applications such as fuel conversion. However, its highly transient nature poses a problem for controlled plasma enhancement studies. A novel magnetically stabilized gliding arc discharge (MGA) is designed such that it can be coupled with a counter-flow burner system for the study of plasma enhanced ignition and combustion processes. The experimental development and characterization of the MGA is discussed. The second part of the thesis deals with a modeling study of production of atomic fluorine (F) using remote (warm) toroidal plasma source and its transport for cleaning of CVD chambers off silicon-based deposits is pursued. Commonly used etchant gases such as CF₄ entail the deposition of carbonaceous compounds on the chamber surfaces. They also produce perfluorocarbons (PFCs) that have global warming implications. Lately, NF₃ is being used as a substitute since its dissociation products are mostly F and N₂. A zero-dimensional chemical kinetic model is used to describe the production of atomic F from NF₃. The transport model uniquely combines both physical (diffusion, adsorption and desorption) and chemical processes (surface and three-body volume recombination) into a reduced kinetic mechanism. This helps us parametrically study the system factors contributing to fluorine recombination and suggest optimal conditions for operation.

Experimental and modeling study of warm plasmas and their applications

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Experimental and modeling study of warm plasmas and their applications

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