A shock wave supported by an atmospheric breakdown plasma caused by a highpower millimeter-wave beam was studied. The shadow graph image in a shock tube visualized the one-dimensional shock-wave generated by the millimeter-wave breakdown in atmosphere for the first time. It was revealed that a normal shock wave propagated through the tube at the constant velocity while it was detached from the ionization front of the plasma whenever the propagation velocity of the ionization front was supersonic or subsonic. And it was visually clarified that the atmospheric millimeter-wave breakdown had the combined structure of the normal shock wave and the heating region of the millimeter-wave plasma. The measured pressure of the shock front was as equal as the normal shock which propagated at measured Mach number.

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The Microwave Rocket is a propulsion system powered by a millimeter-wave beam. In this research, a 170GHz high power gyrotron was used as a microwave source. A pressure history was measured in a cylindrical thruster model with a forced breath system and thrust impulse was estimated from the measured pressure histories at the thrust wall. As a result, dependency of thrust impulse on the partial filling rate of breathed air was obtained. When the partial filling rate is less than unity, that means the air in the cylinder was not fully replaced by fresh air, the impulse decreased with the pulse counts. The prediction by an analytical engine cycle model based on a Pulse Detonation Engine model showed a good agreement with the measurement.

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