AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS-ThP

Paper PS-ThP46
Diagnostic Study of Plasmas in Solution Driven by Pulsed Power - Study of History Effect and Observation of S2 Emission

Thursday, November 1, 2012, 6:00 pm, Room Central Hall

Session: Plasma Science and Technology Poster Session
Presenter: C.Y. Sie, National Taiwan University, Taiwan, Republic of China
Authors: C.Y. Sie, National Taiwan University, Taiwan, Republic of China
C.C. Hsu, National Taiwan University, Taiwan, Republic of China
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Diagnostic studies of plasmas in salt solutions are performed. The plasma is sustained by a pulse power source with the pulse voltage up to 600 V, Ton (voltage on duration) between 10 μs to 1 s, and Toff (voltage off duration) between 30 μs to 3 s. The driving electrode is made of a platinum wire with a diameter of 0.5 mm covered by a glass tube to precisely define the area in contact with the solution. The grounding electrode is a bare platinum wire with the same diameter with a length of approximately 1 cm. The power electrode is set upward and both electrodes are immersed in salt solution. Current and voltage probes are used to monitor the current and voltage waveforms, respectively. An optical emission spectrometer is used to monitor the emission spectra generated by the plasma. In the first part, we demonstrate the observation of the history effect. With a sufficiently short Toff (less than 100 ms), the history effect, i.e. the plasma generated in one power cycle is consistently affected by that generated in the previously cycle, is observed when NaNO3 solution are used. With the history effect, the maximum current within a power cycle increases with cycles, from the first cycle upon Ton. With a sufficiently long Toff (~2 s), good cycle to cycle reproducibility is observed, and the current waveform in each cycle is nearly identical. The history effect is therefore fully eliminated. The transition characteristic time is 0.1 to 1 s, which suggests heating of the electrode is the major mechanism for the history effect. In the second part, we show the detection of S2 emission when the plasma is ignited in low concentration Na2SO4. The intensity of S2 emission gradually drops to the noise level with a long operating time. This observation suggests that the optical emission emanating from the plasma involves a more complex pathway than those suggested in the literature.