Dynamics of Ring-to-Volume Discharge Transition in H Mode in Inductively Coupled Plasma Torches at Atmospheric Pressure

The transition process in ring-to-volume discharge in H mode in inductively coupled plasma torches at atmospheric pressure is investigated by analyzing the time resolved image taken by a high speed camera. The effects of input power, plasma working gas flow rate, and its composition on the transition dynamics are also discussed.The results show that the discharge plasma has experienced ring discharge, and the development stage diffused from the boundary to the center in the confinement tube, and steady volume discharge after entering the H mode. Increasing input power, sheath gas flow rate and hydrogen contents in plasma working gas are all able to lessen the time consumed in the transition process in ring-to-volume discharge.     

Atmospheric pressure plasma jet utilizing Ar and Ar/H_2O mixtures and its applications to bacteria inactivation

An atmospheric pressure plasma jet generated with Ar with H2O vapor is characterized and applied to inactivation of Bacillus subtilis spores. The emission spectra obtained from Ar/H2O plasma shows a higher intensity of OH radicals compared to pure argon at a specified H2O concentration. The gas temperature is estimated by comparing the simulated spectra of the OH band with experimental spectra. The excitation electron temperature is determined from the Boltzmann’s plots and Stark broadening of the hydrogen Balmer Hβline is applied to measure the electron density. The gas temperature, excitation electron temperature, and electron density of the plasma jet decrease with the increase of water vapor concentration at a fixed input voltage. The bacteria inactivation rate increases with the increase of OH generation reaching a maximum reduction at 2.6%(v/v) water vapor. Our results also show that the OH radicals generated by the Ar/H2O plasma jet only makes a limited contribution to spore inactivation and the shape change of the spores before and after plasma irradiation is discussed.