Radical Behavior in Sub-atmospheric Pressure Pulsed Barrier Discharge
ORAL · Invited
Abstract
Atmospheric-pressure cold plasma (APCP) exhibits high chemical reactivity and valuable applicability to various targets. APCP produces high-density radicals, whereas it has the short radical lifetime due to frequent collisional deactivations. To address this issue, sub-atmospheric pressure is an effective way to extend the radical lifetime without the sacrifice of target variety. However, the behavior of radicals in sub-atmospheric pressure is still under investigation. In this study, we measured the behavior of N and O atoms in needle-to-sphere pulsed barrier discharge in sub-atmospheric pressure, using TALIF spectroscopy.
In pure N2 discharge, the discharge regime was transferred from a filamentary form to a diffusive form like a glow discharge at 30 kPa, indicating the improvement of the treatment uniformity. The time evolution of N density exhibited the extension of lifetime with decreasing pressure, while the peak density kept the same level. Consequently, the N atom yield near the electrode became almost double by changing pressure from 90 kPa to 30 kPa.
As for O behavior in pure O2 discharge, the pressure dependence of O production near the cathode took a maximum at 50 kPa, while the lifetime of O atom increased as the pressure was reduced. The O atom yield near the cathode was five times larger than that in atmospheric pressure. The specific production of atomic oxygen near the glass surface was observed, which was due to spreading O-productive region along the barrier surface.
For further improvement of O production, O atom behavior in He-O2 mixture was also investigated. By changing the O2 fraction at 50 kPa, maximum O production near the cathode was achieved at 50-70% O2, whereas the O lifetime was monotonically extended with decreasing O2 fraction. In addition, O production in the afterglow period was observed at 70% O2 fraction or lower. In pressure dependence of O production at 50% O2, atomic oxygen yield near the cathode was maximized at 50-70 kPa.
The above results indicate that the atomic radical yield near the electrode can be enhanced using sub-atmospheric pressure plasma in the range of 30-70 kPa.
In pure N2 discharge, the discharge regime was transferred from a filamentary form to a diffusive form like a glow discharge at 30 kPa, indicating the improvement of the treatment uniformity. The time evolution of N density exhibited the extension of lifetime with decreasing pressure, while the peak density kept the same level. Consequently, the N atom yield near the electrode became almost double by changing pressure from 90 kPa to 30 kPa.
As for O behavior in pure O2 discharge, the pressure dependence of O production near the cathode took a maximum at 50 kPa, while the lifetime of O atom increased as the pressure was reduced. The O atom yield near the cathode was five times larger than that in atmospheric pressure. The specific production of atomic oxygen near the glass surface was observed, which was due to spreading O-productive region along the barrier surface.
For further improvement of O production, O atom behavior in He-O2 mixture was also investigated. By changing the O2 fraction at 50 kPa, maximum O production near the cathode was achieved at 50-70% O2, whereas the O lifetime was monotonically extended with decreasing O2 fraction. In addition, O production in the afterglow period was observed at 70% O2 fraction or lower. In pressure dependence of O production at 50% O2, atomic oxygen yield near the cathode was maximized at 50-70 kPa.
The above results indicate that the atomic radical yield near the electrode can be enhanced using sub-atmospheric pressure plasma in the range of 30-70 kPa.
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Publication: Journal of Applied Physics, Vol. 131, 113304 (2022)
Presenters
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Yusuke Nakagawa
Tokyo Metropolitan University
Authors
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Yusuke Nakagawa
Tokyo Metropolitan University