Takamasa Ishigaki*, Tadahiro Sakuta**, Makoto Katsuki** and Taisuke Tanaka#

*National Institute for Research in Inorganic Materials 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan
ishigaki@nirim.go.jp

**Department of Electrical and Computer Engineering, Kanazawa University Kodatsuno, Kanazawa-shi, Ishikawa 920-0942, Japan

# Nisshin Flour Milling. Co., Ltd. Tsurugaoka, Oi-machi, Saitama 356-0045, Japan

Recently, the RF induction plasma of sufficiently high electric power for materials processing has been successfully generated, for the first time, with a pulse-modulated operating condition[1]. At the time instance of pulse on and off, the steep overshoot and undershoot were recognized giving an abnormally large current flow in the electric circuit and some of transistors were broken. The shimmer level was introduced for decreasing the magnitude of overshooting and the low power level was almost 1/3 of the higher one. In this work, the electrical circuit was modified to increase very slightly the rise and decay time of RF current, with the intention of lowering further the low power level. Typically, when the Ar-H2 plasma was generated at a high power level of 17 kW at atmospheric pressure, the low power level went down to about 4 kW, i.e. below 1/4 of the higher level. The stable generation range was determined for various parameters: the high and low power levels, the duration of pulse-on and -off time, and the reactor pressure. Also, the range was determined for the Ar-N2 plasma generation.

[1] T. Ishigaki, X. Fan, T. Sakuta, T. Banjo and Y. Shibuya, "Generation of Pulse-Modulated Induction Thermal Plasma at Atmospheric Pressur", Appl. Phys. Lett., 71, 3787 (1997).