Investigation of Acoustic Wave Generation in a Microwave Atmospheric Pressure Plasma Jet

The study of acoustic waves in plasma has garnered considerable interest due to their diverse applications [1]. In our present work, an acoustic wave with audible ranges wave observed with microwave atmospheric pressure plasma jet in continuous mode (CW) at two specific power ranges, i.e., 220-360 W, and 570-620 W. Experiments were performed under varying argon gas flow rates (3–12 lpm), an air swirl flow of 45 lpm, a water cooling flow rate of 6 lpm, and changing sliding short positions to elucidate the mechanisms underlying acoustic wave generation. The acoustic waves are recorded using a microphone and analyzed via Fast Fourier Transform (FFT) implemented in MATLAB. During acoustic wave generation, fluctuations in the plasma coloumn were observed and characterized using Optical Emission Spectroscopy (OES) to determine the fluctuations in electron number density (n_e), and electron excitation temperature (T_exc) [2]. The fluctuations in gas temperature (T_g) are measured using a K-type (200-1200⁰C) thermocouple, while high-speed imaging techniques are employed for capturing the fluctuations of plasma plumes. Preliminary results suggest that the generation of acoustic waves near the applicator could be attributed to interference effects between surface waves (SW) [3]. Comprehensive experimental characterizations and underlying physical interpretations will be presented in detail.



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[1] G. A. Galechyan, “Acoustic waves in plasma,” Physics-Uspekhi, vol. 38, no. 12, p. 1309, 1995, doi: 10.1070/PU1995v038n12ABEH000123.

[2] R. Zaplotnik, G. Primc, and A. Vesel, “Optical emission spectroscopy as a diagnostic tool for characterization of atmospheric plasma jets,” Appl. Sci., vol. 11, no. 5, pp. 1–22, 2021, doi: 10.3390/app11052275.

[3] M. Moisan and H. Nowakowska, “Contribution of surface-wave (SW) sustained plasma columns to the modeling of RF and microwave discharges with new insight into some of their features. A survey of other types of SW discharges,” Plasma Sources Sci. Technol., vol. 27, no. 7, p. 73001, Jul. 2018, doi: 10.1088/1361-6595/aac528.