Time resolved optical emission spectroscopy in power modulated atmospheric pressure plasma jet
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| Year of publication | 2013 |
| Type | Conference abstract |
| MU Faculty or unit | |
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| Description | Microwave discharges at atmospheric pressure, especially surface wave sustained discharges have flexible operating conditions which provide a wide range of processing applications. Previously we have used surfatron jet in continuous wave (CW) regime of power supply for material surface activation. However, it might be beneficial to use amplitude modulated (AM) regime instead of CW regime. AM mode enables us to use higher percentage of molecular gas admixture and modulation with specific frequencies also leads to longer and wider plasma flame. Recently, we have investigated what is happening during one modulation pulse. As the used modulation frequency ranges from tens to thousands of Hz, we decided to use time resolved optical emission spectroscopy (OES). The OES was carried out in the plasma flame blown out from the discharge tube. We used argon as the working gas, without any intentional admixtures, except for the admixtures mixing-in from the surrounding air. The attention was given to relative intensities of five spectral features, while 4 of them were present in discharge due to these air admixtures. We compared the trends for different modulation frequencies. It was found out that all line intensities responded to a low frequency (80 Hz) sinusoidal modulation signal quite accurately. As the frequency increased, significant irregularities appeared, especially around the power maximums. To explain their presence in the spectrum for high frequency modulation, macroscopic processes, like air-intake due to gas expansions and contractions, have to be taken into account, as these processes can not instantaneously follow the modulation of power, when it is too fast. Another hypothesis suggests connexion between intensity development irregularities and plasma filament tearing off, creating certain kind of plasma bullets. |
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