SCIENCE SEMINAR
Characterisation of an atmospheric cold plasma produced by a dielectric barrier discharge, using optical emission spectroscopy
Dr. Anca Marina Ionascut Nedelcescu
University of Sherbrooke
Friday, October 2, 2009
1.30 p.m.
Nicolls 1
Cold plasmas are non-equilibrium systems. Consequently, understanding their main physical phenomena as well as determining the temperature and particle density represent key factors in characterising such plasmas. This seminar presents how optical emission spectroscopy is applied to determine the temperature and particle density, and to elucidate the main physical phenomena: Doppler, Stark and Van der Waals effects in a cold plasma. The different excitation temperatures such as electronic excitation, rotational and vibrational temperatures are calculated and compared. The spectral line broadening analysis of the He (587.5 nm) and the Hß emissions is used to evaluate the Doppler, Stark, and Van der Waals effects, as well as to calculate the gas temperature. Due to the superposition of many broadening mechanisms on the same emitted line the analysis is complex. We present a new method to determine directly the gas temperature by incorporating all the broadening dependencies in a unique parametric equation. The method is applied for both He and Hß lines, each of which presents a distinct equation. The electron density is determined from the Stark effect in Hß line. Finally, the gas and the rotational temperature - usually employed to evaluate the gas temperature - are compared and the result indicates that the rotational temperature overestimates the gas temperature. The conclusion confirms the utility of this newly developed method to determine the gas temperature in non-equilibrium plasmas.
