Cavity perturbation technique for determining the presence of molecular ions of helium in a dc discharge plasma

A resonant cavity technique was employed as a probe to determine the presence of molecular ions of helium. The cavity resonance profile was displayed on an oscilloscope and the nature of the perturbation of this resonance observed to determine the nature of ions in a plasma filament placed coaxially within the cavity. The Slater perturbation technique for resonant cavities was employed to calculate relative ion abundances for each type of helium ion observed to be perturbing the resonant frequency of the cavity. The results of this work indicate that for specific currents, voltages and pressures, for a given geometry discharge tube, various molecular ions of helium can be produced and analyzed by the cavity perturbation technique.