Propagation of Microwave Discharge Sustained by Surface Wave in Quartz Tube Filled with Low-Pressure Air
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TEMPERATURE PLASMA
Propagation of Microwave Discharge Sustained by Surface Wave in Quartz Tube Filled with Low-Pressure Air V. I. Zhukova,*, D. M. Karfidova, and K. F. Sergeicheva a Prokhorov
General Physics Institute of the Russian Academy of Sciences, Moscow, 119991 Russia *е-mail: [email protected] Received December 18, 2019; revised March 12, 2020; accepted March 26, 2020
Abstract―Propagation was studied of the ionization front of the gas discharge sustained by the microwave surface wave in a quartz tube filled with low-pressure air. In a wide pressure range, the characteristic propagation velocities of the discharge front were measured, as well as the parameters of the stationary plasma column. The experimental results obtained are in satisfactory agreement with the discharge propagation model based on the concept of nonlocal electron heating in the plasma resonance region. The electrodynamic characteristics of the discharge were studied and the electron density averaged over the cross section of the plasma column was measured. Based on the experimental measurements of the ionization and electron loss rates, the electric field distribution was estimated in the ionization front region. Keywords: low-pressure microwave discharge, quartz tube, surface electromagnetic wave (SEW), ionization front, discharge propagation, plasma resonance DOI: 10.1134/S1063780X20080127
1. INTRODUCTION The first studies of the surface wave propagation in plasma were carried out in the 1950th by Trivelpiece and Gould [1, 2]. This field of research started to rapidly develop after the different methods for the discharge excitation [3] were discovered based on the surface electromagnetic wave (SEW) propagation in the radio transparent tubes. The characteristic feature of such discharges is the fact that the electromagnetic energy supplied to the applicator can be converted with high efficiency into the surface wave, which sustains the self-consistent discharge propagation. The discharges of this type can be used in various applications, such as the plasma processing, plasma chemistry, and plasma antennas [4]. Along with the discharges sustained by the surface waves propagating in the dielectric tubes, since the 2000s, a new field of research is being developed, namely, the studies of microwave discharges initiated on the outer surfaces of dielectric objects by the surface waves [5, 6]. Similar to the discharge inside the dielectric tubes [4], such a discharge makes it possible to create the large-volume plasma with the high electron density considerably exceeding the critical density. The discharges of this type form a self-consistent system in the form of a plasma waveguide, in which the SEW propagates and, at the same time, creates it. In other words, for the existence of a surface wave, the plasma medium is required that is created by the same surface wave [7, 8]. The propagation velocity of the discharge sustained by
the SEW can considerably exceed the speed of sound in the gas used, which allows using these discharg
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