Discharge Characterization Of The DBD In Mixture Gases With CH₃I

Extensive researches on the iodine atom production technology for Chemical Oxygen Iodine Laser have been performed in recent years, using numerous technical methods. DBD jet-like plasma has been adopted in investigation for iodine atom production via iodine-containing compound decomposition for its simple structure, high efficiency and low interruption for the Chemical Oxygen Iodine Lasing process. In this dissertation, discharge characterization is performed on a kind of supersonic DBD plasma jet of mixture gases with CH3I to produce iodine atoms through CH3I decomposition. By using N2and Ar as carrier gases, CH3I is carried into the discharge gap. With the self-designed coaxial pin to ring electrode configuration, a stable discharge can be ignited in all the mixture gases and a controllable jet plasma environment can be achieved by a supersonic nozzle.To electrically characterize the discharges, a mathematical scheme is developed to obtain the discharge conduction current with a high S/N ratio through subtracting the displacement current from the overall discharge current waveforms. The influence of carrier gases, pressure and applied voltage, mixing ratio of CH3I, power frequency on discharge current waveforms is investigated in detail and the discharge mode evolution is analyzed.The discharges are sustained in gas mixtures with CH3I ratio of1.5%-25%and pressure ranging from800-17000Pa by applying driving voltage from0.5kV to6kV in amplitude with frequencies of18kHz,40kHz and100kHz. It is proved that stable plasma jets is produced in the downstream with pressure of1000-2200Pa. Based on conduction current waveform measurement, all discharges are assigned to one identical discharge mode.By measuring the emission spectra within300nm to950nm,4strongest lines of iodine atom and the specific bands or lines of N2and Ar are recorded. Based on the spectra, the relation of the spectral emission intensities to the discharge parameters is explored to probe the electron mean energy and the CH3I decomposition. And then, by combining the discharge electrical characterization; iodine atom transportation process and the loss mechanism are discussed schematically.