Frequency dependence of atmospheric millimeter wave breakdown plasma

The propagation velocity of developing breakdown plasma head generated on the straight beam was measured for 203 GHz / 170 GHz / 137 GHz using a multi-frequency gyrotron. As a result, the propagation velocity has small dependence on frequency. The numerical calculation was conducted for similar condition and the gas heating by plasma was found dominant for growth process of plasma development for this power density range and numerical results presented similar propagation velocity dependence.