Experimental study of gas flow rate influence on a dielectric barrier discharge in helium

A systematic study was performed to investigate the influence of gas flow rate on a helium dielectric barrier discharge. A closed-chamber barrier discharge with plane electrodes was examined through electrical and spectroscopic measurements for a set of gas flow rates varying from 0.05 l min(-1) to 5 l min(-1). The work was concentrated on the presumed connection between the gas flow rate and the impurity level, and consequential change of the discharge operation. A method was developed for estimation of impurities from the emission spectrum and applied in our discharge. The obtained results showed a strongly non-linear decrease of impurities concentration with increasing flow rate of the working gas. Experimental results showed a significant change of electrical properties, like breakdown voltage and current density with the gas flow. The measured electric field distribution did not show important change. The increase of the gas electrical capacitance with gas flow rate was detected, due to the rise of the transferred charge. The intensity of atomic and molecular emissions, along with space time development of certain emissions indicated the change in excitation mechanism with the variation of the gas flow. Analysis shows that the main mechanism of the changes in the discharge is the decrease of impurities, which leads to reduction of helium metastable quenching which, in turn, increases the density of helium metastables important for ionization and excitation processes. The obtained results mostly agree with the models of the discharge behavior with change of impurity level.