Development of a pulse modulated sub-radio frequency power supply for atmospheric pressure plasma devices

The effect of pulse-modulated sub-RF range (100 kHz-1 MHz) excitation on atmospheric pressure argon plasma jet characteristics is studied. For this, a suitable power supply is developed, offering a sub-µs rise time with control of different parameters, such as voltage amplitude, pulse modulation frequency in the range of 1-30 kHz, and an oscillation frequency of ∼520 kHz, which can affect the plasma behavior. Plasma characteristics, such as reactive species generation, ionic composition, plasma plume length, and gas temperature, are evaluated qualitatively and quantitatively by employing diagnostics such as optical emission spectroscopy, molecular beam mass spectrometry, and optical imaging. Experimental observations indicate that the gas temperature of the plasma jet and plume length increase with the applied voltage for all pulse modulation frequencies, with a maximum value of ∼(325 ± 2 K) and a maximum length of ∼(23 ± 3 mm), respectively, at 30 kHz and 9 kVpp. The emission intensities of OH• and O• lines show an incremental behavior with the applied voltage across all pulse modulation frequencies. The relative yield of different positive (OH+, O+, etc.) and negative (OH-, O-, etc.) ions also increases with the applied voltage for all pulse modulation frequencies with maximum values of ∼(7.6%, 9.9%) and (3.9%, 9.4%), respectively; these are relatively close to RF excited ionic concentrations reported previously. Attaining a high plasma length and species yield signify the features of both kHz and RF atmospheric plasmas. This study offers significant insights and flexibility into exploring the impact of different RF frequency regimes on plasma characteristics.