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.

A KHz frequency cold atmospheric pressure argon plasma jet for the emission of O(1S) auroral lines in ambient air.

Creation of the "auroral" green line, a fascinating occurrence commonly observed in the upper atmosphere, has long been a difficult endeavor, especially at atmospheric pressure. Here we report strong emission of the "auroral" green line for the first time in a kHz frequency, linear field atmospheric pressure plasma jet system. The device used 99.999% pure argon as a working gas for the plasma generation. Optical emission spectroscopy measurements of the after discharge region show the existence of 557.7 nm emission which corresponds to the transition O([Formula: see text]S)-O([Formula: see text]D). The intensity of the produced green line is strong enough that the entire plasma plume in the ambient air is visible as a green plasma. We provide the chemical reactions of O([Formula: see text]S) production in the plasma and the estimation of the density of the O([Formula: see text]S) metastable state using the kinetic reactions. Further, the O([Formula: see text]S) emission is characterized by changing the flow rate of argon, applied voltage and electrode gap. The adequate plasma length ([Formula: see text]) along with the production of a variety of reactive components viz; OH, [Formula: see text] and oxygen (777 nm) make this configuration useful for applications such as: blood coagulation, cancer treatment, sterilization, and waste treatment. Moreover, this setup can be potentially used as a test bed for the in-depth understanding of plasma chemistry relevant to the aurora and comet tails using a laboratory setting.