Numerical analysis of plasma structure observed in atmospheric millimeter-wave discharge at under-critical intensity.

Atmospheric millimeter-wave discharge at intensity on the order of 1 GW/m2, which is lower than the critical intensity for breakdown by one order, was computed numerically using a tuning parameter to reproduce a wavelength-scale discrete plasmoid structure in a propagating ionization front observed in experiments. In this structure, the plasmoids line up along the <bold>E</bold> field of the incident beam in the same pitch of 0.9λ. Computational results showed that the structure appears when the electron number density in the plasmoid is greater than the cutoff density of 2.5 × 1020/m3. Interference among an incident wave and reflection waves from a plasmoids produces fringes around the plasmoid. Neighboring plasmoids come to the enhanced point, which is placed at a distance of 0.9λ from the plasmoid center. This knowledge related to the structure is expected to be correct irrespective of the plasma modeling because the revealed forming mechanism is dependent only on the geometrical interference between the incident and reflection. [ABSTRACT FROM AUTHOR]