A Novel Active Needle Probe in an Atmospheric Pressure Corona-Based Cold Plasma Reactor With Admixtures of Helium and Dry Air

Corona-based atmospheric pressure cold plasma reactors can be applied to material processing, bacteria inactivation, plasma medicine, etc. Knowledge generated in this article can be used to optimize such reactors when they use electrodes consisting of arrays of needles. The experiment used a gas admixture of helium and dry air and an applied 60-Hz ac voltage of 6.5-kV rms, with an electrode gap of 6 cm. A novel single conducting needle probe was inserted into the corona gap from below the grounded electrode. Two distinct conduction and displacement current signals were captured by a digital oscilloscope: 1) current collected by the probe and 2) current collected by the grounded electrode. Current oscillograms were sorted into several classes, one of which showed evidence that corona pulses launched from the tip of the needle probe acted to shield surrounding portions of the grounded electrode resulting in distinct counter pulses of current (called shielding current pulses) observed at the grounded electrode current sensor. This needle probe has the ability to provide information regarding which electrode launches a corona pulse when both needle arrays (the high-voltage array and the grounded array) are known to be sources of corona discharges.