Plasma generation using high-power millimeter-wave beam and its application for thrust generation

Propagation of an ionization front in the beam channel was observed after plasma was generated using a $170\mathrm{GHz}$ millimeter-wave beam in the atmosphere. The propagation velocity of the ionization front was found to be supersonic when the millimeter-wave power density was greater than $75\mathrm{kW}{\mathrm{cm}}^{-2}$ . The momentum coupling coefficient $C_m$ , a ratio of the propulsive impulse to the input energy, was measured using conical and cylindrical thruster models. A $C_m$ value greater than $350\mathrm{N}{\mathrm{MW}}^{-1}$ was recorded when the ionization front propagated with supersonic velocity.