Phenomenology of Corona Discharge in Helium Admixtures Inside a Point-to-Point Electrode Geometry

Experimental investigations of the electrical discharge characteristics were performed primarily for helium admixtures in a point-to-point electrode geometry. The atmos- pheric pressure weakly ionized plasmas were generated using 60-Hz ac excitation voltage that generated a corona discharge without dielectric barriers on the electrodes. The admixtures used were helium/acetylene (He/C
₂
H
₂
), helium/oxygen (He/O
₂
), and helium/dry-air (He/air) with comparisons made to corona discharges in an admixture argon/dry-air (Ar/air). Visual observations along with voltage-current characteristics have been presented. The discharge included streamers, glows, and return corona discharges inside the point-to-point high voltage gap. We developed from experimental data corona mode maps to delineate optimal regions for plasma operation in these admixtures. Helium carrier gas developed sufficient discharge power when mixed with acetylene, oxygen, or dry air. Peak discharge power was in the range 3-20 W and depended on the polarity of the voltage cycle being considered and depended also on chemical species in the admixture.