摘要A weakly luminous layer close to the anode is observed at time far ahead of the current pulse in dielectric barrier discharge of helium at atmospheric pressure and it is considered as the result of a very weak Townsend discharge. Based on the assumption that the space charge produced by this Townsend discharge is too small to distort the uniform electric field in the gas gap, the electrons have more or less the same energy over the entire gap and the spatial distribution of the discharge light is proportional to the distribution of electron density. This light distribution is obtained by processing side-view photograph of discharge gap using an intensified charge coupled device camera with an exposure time of 20ns. By fitting a theoretically derived formula with the measured curve of light distribution, the Townsend electron ionization coefficient α is determined to be 31cm-1 at E/p=3.6V・cm-1・Torr-1, which is much higher than that obtained by solving the Boltzmann equation of pure helium. It is believed that penning ionization of helium metastables with impurity of nitrogen molecules makes great contribution to the experimentally determined α value. The contribution of this penning ionization to α is roughly estimated.
Abstract：A weakly luminous layer close to the anode is observed at time far ahead of the current pulse in dielectric barrier discharge of helium at atmospheric pressure and it is considered as the result of a very weak Townsend discharge. Based on the assumption that the space charge produced by this Townsend discharge is too small to distort the uniform electric field in the gas gap, the electrons have more or less the same energy over the entire gap and the spatial distribution of the discharge light is proportional to the distribution of electron density. This light distribution is obtained by processing side-view photograph of discharge gap using an intensified charge coupled device camera with an exposure time of 20ns. By fitting a theoretically derived formula with the measured curve of light distribution, the Townsend electron ionization coefficient α is determined to be 31cm-1 at E/p=3.6V・cm-1・Torr-1, which is much higher than that obtained by solving the Boltzmann equation of pure helium. It is believed that penning ionization of helium metastables with impurity of nitrogen molecules makes great contribution to the experimentally determined α value. The contribution of this penning ionization to α is roughly estimated.
[1] Raether H 1964 Electron Avalanches and Breakdown inGases (London: Butterworths) p 1 [2] Davies D K 1976 J. Appl. Phys. 47 1920 [3] Tsumaki K 1988 Jpn. J. Appl. Phys. 27 393 [4] Banford et al 1977 J. Phys. D: Appl. Phys. 10 2177-2180 [5] Raizer Y P 1991 Gas Discharge Physics (Berlin:Springer) p 56 [6] Luo H et al 2007 Appl. Phys. Lett. 91 221504 [7] Massines F et al 1998 J. Appl. Phys. 83 2950 [8] Bates D 1962 Atomic and Molecular Processes (NewYork: Academic) p 337 [9] Golubovskii Y B et al 2002 J. Phys. D: Appl.Phys. 35 751 [10] Li M et al 2008 Appl. Phys. Lett. 92 031503 [11] The Siglo Data Base, CPAT and Kinema Software,http://www.siglo-kinema.com [12] Specht L T et al 1980 J. Appl. Phys. 51 166 [13] Golden D E and Fisher L H 1961 Phys. Rev. 1231079 [14] Nersisyan G et al 2004 Appl. Phys. Lett. 85148 [15] Yuan X et al 2003 IEEE Trans. Plasma Science 31 495
2008, Vol. 25 
