Plasma generation at atmospheric pressure using a high-power microwave beam and its application to rocket propulsion

大電力マイクロ波ビームによる大気圧下でのプラズマ生成とそのロケット推進への応用

小田 靖久*; 小紫 公也*; 高橋 幸司; 春日井 敦; 今井 剛*; 坂本 慶司

Oda, Yasuhisa*; Komurasaki, Kimiya*; Takahashi, Koji; Kasugai, Atsushi; Imai, Tsuyoshi*; Sakamoto, Keishi

170GHz, MW級ジャイロトロンを応用し、マイクロ波プラズマ生成とマイクロ波推進器の実験を行った。推進器内で発生したプラズマはマイクロ波の進行方向とは逆方向に向かって伝播し、その伝播速度は、マイクロ波のパワー密度が75kW/cm以上になると音速程度になることが判明した。また、推進力を測定したところ、運動量結合係数はプラズマの伝播速度が音速になると最大になることも判明した。これはプラズマ圧力が効率よく上昇し、その結果強い衝撃波を生み出す結果となっていると考えられる。

Experiments on microwave plasma generation and its application to microwave beamed energy propulsion were conducted using a 1 MW-class, 170 GHz gyrotron. The microwave beam was focused using a parabola reflector and plasma was initiated near the focal point in the ambient air. Plasma propagated upstream in the microwave beam channel while absorbing microwaves. Its propagation velocity was supersonic when the microwave power density was greater than 75 kW/cm. The propulsive impulse was measured using a cone-cylinder shaped thruster model. As a result, the maximum momentum coupling coefficient was obtained at a certain plasma propagation distance. In addition, a larger momentum coupling coefficient was obtained when plasma was propagated at a supersonic velocity. This is because supersonic plasma propagation forms a strong shock wave, resulting in an efficient pressure increase.