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FO-Tatarinov_e

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									           39th international conference on plasma physics and CF, February 6 – 10, 2012, Zvenigorod.



STRONGLY NON-UNIFORM MICROWAVE DISCHARGE IN NITROGEN WITH SMALL
       ADDITIONS OF HYDROGEN: EXPERIMENT AND 2D MODELING
                 J. Jovovich, N. Konjevic, Yu. Lebedev*, A. Tatarinov*, I. Epstein*
      Physical Department, Belgrade University, Belgrade, Serbia
      *
        Topchiev Institute of Petrochemical Synthesis RAS, Moscow, Russia, lebedev@ips.ac.ru

   First experiments in strongly non-uniform plasma of microwave electrode discharge (EMD) in
nitrogen at pressure 1 Torr showed that small additions of hydrogen have an influence on intensities
of the second positive system of nitrogen in the peripheral (spherical) part of the discharge [1]. This
paper presents results of detailed experimental joint study of this effect in Physics Department of
Belgrade University and results of 2D modeling carried out in TIPS RAS.
   Experimental setup was similar to that used in [1], it differed in characteristic dimensions and is
fully described [2]: the diameter of discharge cylindrical chamber was 82 mm, incident power was
up to 375 W, microwave frequency was 2.45 GHz. The discharge image was projected onto the
entrance slit of the monochromator by a system of lens and mirrors. The air-cooled CCD (2048 x
506 pixels, pixel width 12 mm) was used as a radiation detector. Measurements allowed to obtain
spatial distributions of lines and bands both in the near-electrode and spherical parts of the
discharge. Concentration of hydrogen in the mixture was 0, 1, and 5 %.
   The model for nitrogen EMD [3] has been modified for description of the nitrogen-hydrogen
mixture. The comercial package Comsol 3.5a has been used for simulations of the model.
   Experiments showed that both in pure nitrogen and in the mixture with hydrogen the discharge
dimension increases with increase of the microwave power. Addition of hydrogen reduces the
discharge dimensions, enhances the intensities of emission of the second positive bands of nitrogen
in spherical part of EMD, and reduces the intensities of emission of the first negative system of
nitrogen ion in all parts of EMD.
   The ratio of intensities of the second positive and first negative bands of nitrogen emission was
used for determination of microwave field strength in the near-electrode region nitrogen EMD
assuming the coronal model. This method cannot be used for the mixture with hydrogen as the
coronal model cannot be applied for the first negative system.
   Results of modeling are in the qualitative agreement with results of experiments. Modeling
showed that influence of hydrogen in nitrogen band emission is caused by the high rate of the
conversion of nitrogen ions ( N2+ , N4+ ) to ion N2H+ in collisions with hydrogen.
References
[1]. Yu A Lebedev, T B Mavlyudov, V A Shakhatov and I L Epstein, High Temperature 2010 48
     315-320.
[2]. J Jovovic, NM _Sisovic, N Konjevic. Vacuum 2010 85 187-192
[3]. Yu A Lebedev, A V Tatarinov and I L Epstein, Plasma Sources Sci. Technol. 2007 16 726-
     733




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