The paper presents the results of recent experimental studies. The subject of research was the discharge of atmospheric pressure in a gas stream in focused beams of microwave radiation. The radiation sources were: a gyrotron with a radiation frequency of 263 GHz and a power of up to 1 kW, a free-electron laser with a radiation frequency of 2.3 GHz and with an average power of up to 400 W. The paper presents the results of measurements and calculations of breakdown fields, the results of measuring plasma parameters in these cases. Possible applications are discussed.
This paper presents the results of the studies of the subthreshold discharge propagation under the action of the focused beam of sub-terahertz CW gyrotron (1 kW@0.26 THz). The discharge propagation velocity towards electromagnetic radiation was measured in various noble gases in the wide pressure range (0.1 – 2 atm) for various field intensities into the focal spot (5-15 kW/cm2). It was demonstrated that discharge velocity increase along with pressure decrease and drops with electric field decrease as it moves away from the focal spot. Typical velocity values and discharge spatial structure suggest the so-called equilibrium mechanism of discharge propagation.
Previous experiments performed in IAP RAS showed the possibility of realizing a localized (characteristic size not more than 1 mm in diameter) discharge in an inhomogeneous gas flow by focused sub-terahertz radiation beam. Plasma with an overcritical density up to 3·1016 cm - 3 was obtained. In these experiments, discharge glow was observed both in the range of vacuum (VUV) and extreme (EUV) ultraviolet. The performed experiments demonstrated that in order to increase the yield of EUV, the shorter wavelengths of heating radiation must be used. According to estimations, if the 1 THz radiation with power of several kilowatts is in a good coupling with the plasma, the plasma density will substantially exceed 1016 cm - 3 with electron temperature of the level of 50 eV. This should provide extreme ultraviolet glow of the discharge with power of about 100 W in the range 13-17 nm for xenon.
The spatial-time dynamic of THz nitrogen discharge in the background pressure range from a few torrs to one atmosphere was obtained. The work discuss issues of discharge propagation mechanism and shock wave formation. The radiation source was the gyrotron with maximum pulse power of about 40kW at frequency 0:67THz and duration 20μs. The main diagnostic tool was laser interferometry, based on the analysis of changes in the fringe structures made by a probe beam (r = 12mm at 1=e2 level) crossing the plasma cloud. The Michelson interferometer scheme with a diode laser at 532nm was used.
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