XXXIV International Conference on Plasma Physics and CF, February 12 – 16, 2007, Zvenigorod
ON THE SPATIAL STRUCTURE OF ELECTRODE MICROWAVE DISCHARGE
Yu.A. Lebedev, P.V. Solomakhin, V.A. Shakhatov
A.V. Topchiev Institute of Petrochemical Synthesis RAS, Moscow, Russia,
e-mail: lebedev@ips.ac.ru
Detailed study of structure of the electrode microwave discharge (EMD) was carried out for
nitrogen, hydrogen and argon in the experimental stand EMD-3 [1, 2]. The discharge structure was
studied by means of digital photography and by emission spectra with spatial resolution measured
by spectrometers AvaSpec-2048 and AvaSpec-2048-4-RM in the spectral range 200-850 nm. EMD
was scanned by the optical fiber moved with micrometric table in the direction of discharge axis
and in the radial direction (the spatial resolution was of 100 microns). The solid cylindrical and tube
electrodes were used with external diameter 5 mm. Measurements were made in the flowing system
and the feeding gas was introduced to the chamber through the channel in the electrode or through
the ceiling of the chamber ( the flow rates were up to 200 sccm). The gas pressure in the chamber
was 1-100 Torr and the incident microwave powers were ranged between 30 and 150 W.
It was shown that the gas flow can influence the discharge structure. This influence was
pronounced in argon EMD where, in contrary to hydrogen and nitrogen EMD, the discharge had a
luminous channel structure with the diameter of 1 mm. The length of the channel was of 5 cm and
the end region of the channel was structurized and being the system of successive bright plasma
regions.
EMD in hydrogen and nitrogen had a nonuniform ball-like structure and increase if the flow rate
does not change the ball deformation but produce the bright plasma flow from the ball in the
direction of the gas flow. The barrel-like structures was observed in the plasma flow at flow rates
provided the gas velocity close to the rate of sound.
The structure emission spectra of nitrogen and hydrogen EMD was studied at pressure 1 Torr. It
was shown that EMD is nonuniform and increase of plasma emission was observed near the buttend of the electrode (the “tongue” of emission was spread up to 6 mm from the butt-end). It was
also shown that the plasma exists in the end of the electrode channel. The presence of this “tongue”
does not depend on the method of gas feed. Analysis leads to the conclusion that this peculiarity of
EMD emission can be caused by electron beam decaying in the direction of discharge axis.
The vibrational distribution function for nitrogen state C 3 u was studied. It was shown that the
function slightly depend on the spatial coordinates and temperature of population of the first
vibrational level ranged between 3000 and 7000 K.
Work was partially supported by the Programme #9 for Fundamental Researches of the
Presidium of RAS and grant NWO-RFBR #047.016.019.
Literature
[1]. Lebedev Yu.A., Solomakhin P.V., Shakhatov V.A. Plasma Phys. Rep., 2007, v.33, №1.
[2]. Lebedev Yu. A., Solomakhin P.V., Shakhatov V.A., Epstein I.L. VI International Workshop
Microwave Discharges: Fundamentals and Applications September 11-15, 2006 Zvenigorod,
Russia, Proceedings Ed. by Yu.A. Lebedev, - Yanus-K Moscow, 2006, P.119-12
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