The plasma parameters in a VHF plasma with a narrow gap under high gaseous pressure were experimentally investigated. As a result of the Langmuir probe measurement for hydrogen plasma with a gap length of 5 mm and a pressure of 1 torr, it was found that the electron temperature (∼10 eV) was high enough to promote the dissociation reaction of SiH4 molecules, and that a large amount of negative ions which could play a role in reducing the sheath potential were produced. On the other hand, the results of the ion measurement using a quadrupole mass spectrometer with an energy analyzer indicated that the highest produced ion was H 3+ and its incident energy to the substrate was low due to the collisions. These results suggest that the condition of high pressure and narrow gap are advantageous for the preparation of high‐quality µc‐Si thin films.
A new balanced power feeding method was applied to produce a large area VHF plasma using short discharge gaps and the electric characteristics of the discharge electrodes were measured as a function of pressure for different discharge gaps. It was found that the new balanced power feeding method is suitable for short gap discharges in the VHF range. Furthermore, the plasma parameters were examined as a function of pressure for different discharge gaps. The plasma density peaked at a certain pressure independent of the length of discharge gaps.
In the flow control valve used in the upper or the lower stream of a turbomachinery, when opening is small, the self-induced oscillation resulting from a clearance gap flow may occur. In this study, the mechanism of self-induced oscillation which occurs on the small valve opening condition was examined. And a concept to control the self-induced oscillation was built. The air model test of the flow control valve was carried out, and it was confirmed that self-vibration occurs under specific conditions. Moreover, stability evaluation using CFD was carried out, and it checked that the calculation results become the almost same tendency as a test results. The area where the instability force is generated on a valve was grasped from the simulation results, and it checked that stability was changed with flow field differences. Based on these results, stabilization of the flow control valve was attained by improving clearance gap geometry of the valve sheet area. It checked that the intended flow field was obtained in the geometry in CFD analysis, and it confirmed that fluid additive damping became positive in CFD.
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