Characterization of the behavior of chemically reactive species in a nonequilibrium inductively coupled argon-hydrogen thermal plasma under pulse-modulated operation

Abstract

The temporal and spatial dependence of species densities in a pulse-modulated inductively coupled plasma (PM-ICP) in an argon-hydrogen mixture was investigated by means of numerical modeling, taking into account time dependence, two temperatures, and chemical nonequilibrium, and also through spectroscopic measurements. Conservation equations for mass, momentum, electron energy, heavy-species energy, each species, and the electromagnetic field were developed and solved self-consistently. The transient behavior of the mass fraction of each species was determined by including chemical kinetics source terms in the species conservation equations. Fourteen chemical reactions involving seven species (e, Ar, Ar+, H2, H2+, H, and H+) were considered. The transport properties were evaluated based on the local species densities using the first-order approximation of the Chapman-Enskog method. Time-resolved electron density profiles were obtained from measurements of the Stark broadening of the Hβ line (486.1nm), performed using an optical system positioned using a stepper motor. The investigations were conducted for a maximum power level of 11.7kW with a duty factor of 66.7% and at a pressure of 27kPa. Reasonable agreement was found between the predicted and measured electron densities. The electron density in the discharge region varied considerably over a pulse cycle, while the hydrogen atom density remained high throughout the cycle, and peaked in a region that has been experimentally demonstrated to have optimal efficiency for hydrogen doping of materials. The main mechanisms responsible for the production of the relevant species in the PM-ICP are discussed.