Parameters of a Subthreshold Microwave Discharge in Air and Carbon Dioxide as a Function of Microwave Field at Different
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RACTION OF WAVES WITH PLASMA
Parameters of a Subthreshold Microwave Discharge in Air and Carbon Dioxide as a Function of Microwave Field at Different Gas Pressures K. V. Artem’eva, G. M. Batanova, N. K. Berezhetskayaa, V. D. Borzosekova, A. M. Davydova, L. V. Kolika, E. M. Konchekova, *, I. A. Kossyia, A. E. Petrova, K. A. Sarksyana, V. D. Stepakhina, and N. K. Kharcheva a Prokhorov
General Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected]
Received November 20, 2019; revised March 20, 2020; accepted March 26, 2020
Abstract—Propagation velocity of a subthreshold microwave discharge in air and carbon dioxide is measured at various gas pressures and intensities of microwave radiation. At air pressures of 200, 390, and 738 Torr and carbon dioxide pressures of 390 and 750 Torr, the propagation velocity of the head part of the self-non-selfsustained discharge closely follows a quadratic power law as a function of microwave-beam intensity in the range from 4 to 16 kW/cm2, while decreasing directly proportional to the initial gas density. In the process, the discharge propagation velocities in carbon dioxide are twice lower that those in air at equal intensities of the microwave radiation. The temperature in the head part of the discharge in air reaches 3.5–5.5 kK, while that in carbon dioxide reaches 9–15 kK. Keywords: self-non-selfsustained discharge, subthreshold microwave discharge, gyrotron, location measurements DOI: 10.1134/S1063780X20090019
1. INTRODUCTION Subthreshold wave-beam microwave discharges at high gas pressure are of interest for various plasmachemical applications, including utilization of landfill gases [1–5]. The head part of the discharge propagating toward the incident microwave beam represents a narrow several-centimeter-long localized region moving at a speed of 103–105 cm/s and consisting of appearing and relaxing discharge channels stretched along the electric field that are characterized by high plasma density (~1017 cm–3),1 high gas (~10 kK) and electron (~10 eV) temperatures. It also includes ionized and heated gas between the channels. Propagation of the head part of the discharge towards the incident wave beam is caused by a nonself-sustained microwave discharge in the UV halo of the head part of the discharge and the onset of the ionization-overheating instability inducing a new series of filament discharges in front it. This kind of discharge was actively studied in 1980s at the Prokhorov General Physics Institute, Russian Academy of Sciences (GPI 1 The
possibility of achieving such plasma densities in filament discharges is corroborated by both earlier studies [4] and estimates obtained in our recent works [5] dealing with spectral broadening of Hα radiation in the experiments with methane gas.
RAS, Moscow) and Applied Physics Institute of the Russian Academy of Sciences (API RAS, Nizhny Novgorod). A detailed review of the first experimental works can be found in [6], including the data on measurements of the discharge propagation vel
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