Stability of a high-frequency glow discharge in the normal combustion regime
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A high frequency glow discharge in its high current form differs from a dc discharge in that there is a significant decrease in the role of the pre-anode region in plasma generation , thus leading to greater stability . In a dc discharge the pre-anode current-voltage characteristic (CVC) is falling , which causes electrodynamic instability of the plasma column and leads to its contraction over times much shorter than the thermal times . It is characteristic that conductivity in the volume of a dc discharge at moderate pressures is caused by drift of ions from the pre-anode region. In an hf discharge the plasma distribution is symmetric about the midpoint of the interelectrode gap and the space charge zones near the electrodes are separated from the volume by narrow zones with high conductivity. Under such conditions, together with volume ionization processes a noticeable contribution to maintenance of conductivity can be produced by ambipolar diffusion and plasma drift due to disruption of quasineutrality [5, 6]. In order to study the stability of an hf discharge plasma column it is of interest to find the current-voltage characteristic of this part of the discharge under conditions of high longitudinal inhomogeneity and low values of E/p. In connection with the experimentally observed weak current form of the discharge [1, 2], which is characterized by a unique value of the normal current density and lacks a proper theoretical explanation, there has been increased interest in the properties of the hf discharge which are produced by phenomena in the pre-electrode regions. In particular, it is necessary to theoretically confirm the similar properties of the dc discharge and the hf discharge in the normal current density regime. The present study will present results of a numerical calculation of an hf discharge in nitrogen with consideration of space charge effects within the framework of a two-dimensional model and calculated the CVC of a plasma column with the diffusion-drift mechanism for maintenance of conductivity.
KeywordsGlow Discharge Plasma Column Thermal Time Combustion Regime Space Charge Effect
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