Electrode microwave discharge in nitrogen: Structure and gas temperature
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Electrode Microwave Discharge in Nitrogen: Structure and Gas Temperature Yu. A. Lebedev, P. V. Solomakhin, and V. A. Shakhatov Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskiœ pr. 29, Moscow, 117912 Russia Received March 10, 2006; in final form, April 25, 2006
Abstract—Electrode microwave discharges in nitrogen at pressures of 1–16 Torr and input microwave powers of 30–180 W have been studied by space-resolved emission spectroscopy. It is shown that the discharge is highly nonuniform. The relative intensities of the first and second positive nitrogen bands, as well as of the first negative band of nitrogen ions, are found to vary significantly throughout a discharge because, in different discharge regions, emitting particles are excited by different mechanisms. The gas temperature was determined by the method of the unresolved rotational structure of different sequences of the emission spectra of the second positive system of nitrogen. PACS numbers: 52.80.-s, 52.80.Pi DOI: 10.1134/S1063780X07020109
1. INTRODUCTION Interest in low-power electrode microwave discharge (EMDs) stems from the possibility of using them to produce nonequilibrium plasmas in a wide pressure range in specific spatial regions, create compact plasma structures, generate active particles in large volumes, and form plasmas on the surfaces of bodies of various shape. EMDs allow one to initiate and study plasmochemical processes, intensify gas-phase physicochemical processes (including combustion processes), and investigate the interaction of gas flows with surface plasmas and bulk plasma structures. In recent years, EMDs have attracted special attention because of their highly nonuniform structure. Actively studies on EMDs performed since 1997 have yielded a great body of experimental data on the physical processes in nonequilibrium EMD plasmas and their applications [1–9]. Nevertheless, some problems related to the physics and chemistry of EMDs have gone practically unstudied. Thus, the main emphasis was put on studying hydrogen discharges, in which electron-impact processes play a dominant role. It is, however, very important to investigate how stepwise and associative processes involving excited particles affect the structure and physical properties of an EMD. Such information can be obtained, e.g., in studying EMDs in nitrogen. Unfortunately, there are only a few publications addressing this problem. The spatial distribution of the integral EMD emission was investigated in [5], where the observed difference in the structures of discharges in nitrogen and hydrogen was attributed to different mechanisms for gas-phase processes in these gases. In nitrogen plasma, the processes involving excited particles dominate, whereas in hydrogen, electron-impact processes play a major role. In [5, 6],
where EMDs in nitrogen were studied using the probe technique, it was found that the electron density decreased abruptly at the boundary of the discharge glow region. One of the key parameters of a noneq
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