Rayleigh Microwave Scattering for Diagnostics of Atmospheric-Pressure Microplasmas*

摘要

Summary form only given. Conventional diagnostics cannot be used to measure plasma parameters of atmospheric pressure plasmas if plasma size is small (<;1 mm) and density is low (<;10^{13 cm-3). Microwave interferometry fails due to necessity to choose high testing frequency because of small plasma size, which leads to undetectable phase shift. Laser Thomson scattering has limited sensitivity for measuring plasmas with low ionization degree, namely minimal plasma ionization degree is about 10-6 (~1013 cm-3 for atmospheric pressure discharges), and it requires very significant accumulation of the signal (105-106 pulses) which is problematic in case of rapidly evolving non-reproducible plasmas. This presentation will review fundamentals of Rayleigh microwave scattering for slender prolate plasma geometries. Performance of RMS technique will be analyzed and compared with the conventional microwave interferometry. Examples of plasma density measurements for several types of atmospheric-pressure microplasmas will be considered, namely nanosecond repetitive pulsed discharges, laser-induced plasma filaments in air, atmospheric-pressure plasma jets, electric discharge used in electrosurgery.}