| Summary: | 碩士 === 國立東華大學 === 光電工程研究所 === 97 === Atmospheric pressure plasma does not need expensive vacuum facility, so be welcomed and applied in many areas in the industry. It can be ignited by micro hollow cathode which consists of cylindrical holes of 0.1~0.4 mm, but has a life time issue due to the damage of the electrodes caused by DC power supply. Thus it is important to improve the steady atmospheric pressure plasma, we studied and characterized by plasma diagnostics from the Electron Energy Distribution Function (EEDF).
We made the micro hollow cathode by two metal electrode layer separated by dielectric layer, which spacing is 1 mm determined by Paschen Law, and the diameter of the hole is 0.3 mm dependent on the operating pressure and diameter proposed by F.W. Aston. A 13.56Mhz RF power supply is proposed to improve the life time issue caused from DC power. Plasma is generated in the hole by flowing Argon gas through the electrode, detected by the Langmuir probe, and the electron temperature (Te), plasma density (n) and Electron Energy Distribution Function (EEDF) can be derived from the I-V characteristic. We can therefore realize the relationship of the micro hollow cathode dimension with the operating parameters.
As the pressure increases from 500mTorr to 2Torr, the saturation current decreases from 6.6mA to 1.5mA, and the electron temperature decreases from 4.0eV to 3.1eV. We also find the EEDF in the low pressure has abundant high energy tail, and shows non-Maxwellian profile. That means applied electrical field permeating into plasma and causing plasma instability. The energy of the high energy electron could not transfer to the molecule through collision. In the other hand, electron temperature is about 3.2eV at high pressure, and EEDF is near-Maxwellian profile. Plasma is stable no matter how variation of the power consumption and gas flow.
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