Spectral diagnosis of atmospheric pressure AC argon plasma jet at fixation power: Effects of pulse modulation duty cycle, voltage, and frequency

In the application of atmospheric pressure plasma jet, due to the limitations of AC power supply with the frequency in the ranging of kHz, the study of the influence of power supply electrical parameters on the discharge basically only explore the change rules of plasma jet characteristics varying with a single driving electrical parameter (for example, voltage and frequency) changes. However, the discharge power usually changes in the process of a single electrical parameter change, which undoubtedly also affect the discharge performances including the plasma physical parameters and generated reactive species, resulting that the effect of the single driving parameters on the discharge cannot be reflected. In this study, an atmospheric pressure argon plasma jet is driven by a self-developed AC power supply with adjustable pulse modulated duty cycle. And combined with the diagnosis of the optical emission spectrum and the optical absorption spectrum, the influences of the voltage, frequency and pulse modulated duty cycle parameters on the gas temperature T_g, electron excitation temperature T_exc, electron density n_e, and OH radical particle number density of the plasma jet are studied under a fixation discharge power of 2 W. The results show that at the fixation power, the electron density ne does not change with the variation of electrical parameters as the linkage change of electrical parameters will offset the influence of a single parameter on the electron density, while the gas temperature T_g, electron excitation temperature T_exc, and OH radical particle density are the most affected by the pulse modulated duty cycle, followed by driving voltage, and frequency has the least effect. Under the fixation power, when the frequency is reduced, the voltage will increase, and the gas temperature T_g, electron excitation temperature T_exc, and OH radical particle number density will increase. On the contrary, although the voltage also increases when the pulse modulated duty cycle is reduced, it will lead a decrease in the gas temperature T_g, electron excitation temperature T_exc, and OH radical particle number density. In addition, the results indicate that reducing the duty cycle of AC power can make the atmospheric pressure plasma jet produce more OH radical at lower gas temperature. This study provides a new insight into the influence of electrical parameters on the characteristics of atmospheric pressure plasma jets under a fixation power, and provides guidance for the selection of power parameters of plasma jets with low gas temperature and high density of reactive species, which is conducive to the development of atmospheric pressure plasma jets in biomedicine and other fields.