The paper describes an experimental facility for plasma physics and material science research. The system provides effective transportation of radiation from gyrotron output to the area under investigation inside the vessel, which can be arranged for specific task and equipped with different control and measurement tools. The use of this facility made it possible to realize a series of various experiments, in particular, initiating and studying the fundamental properties of a terahertz discharge, obtaining nanopowders by evaporation-condensation method, as well as measuring the dielectric properties of metal oxide powders. As a radiation source we used 0.26 THz/1 kW gyrotron, which can operate both in CW or pulse mode, gyrotron, the radiation of which can, if necessary, be focused by quasi-optical mirror into a spot with a diameter of about 2.5 mm, providing a power density of up to 20 kW/cm2 in the region of interest. The main components of the facility are described and some results of recent experiments are given.
A technique for imaging of high-power millimeter-wave (MMW) beams using visible light emission from a surfaceinitiated microwave gas breakdown is discussed. A wave beam from pulsed 250 GHz gyrotron was imaged using a microwave gas breakdown initiated by a surface of a metal-dielectric screen. The screen was placed in a shallow metal chamber filled with helium with an admixture of argon. In the region, where MMW intensity was higher than the threshold intensity of the surface-initiated microwave gas breakdown, the intensity profile of a high-power MMW beam, which was obtained using this technique, was in good agreement with the data obtained using the thermographic technique.
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.
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